FOR INTERNAL CIRCULATION ONLY
user’s manual of Construction Soil Investigation & Foundations
Construction Management
Power Grid Corporation of India Limited (A Government of India Enterprise) DOCUMENT CODE NO. : CM/TL/SOIL INVESTIGATION & FOUNDATIONS/FINAL/98
OCT, 1998
CHAIRMAIN & MANAGING DIRECTOR’S MESSAGE It gives me immense pleasure to learn that Construction Management has come out with further four volumes of User’s Manual of Construction : ‘Soil Investigation & Foundations’, ‘Pile & Well Foundations’, ‘Contracts Management’ and ‘Transformers & Reactors’. The various changes in the wake of rapid advances in technologies and growing competition on global basis has made it imperative to conceptualise the methods for optimizing our resources; the 5M’s namely men, money, machines, materials and methods. They are the basics to realize a construction project and time, cost & quality are its critical parameters. The construction of transmission line is a wide canvas and complex in nature that needs a multi disciplinary approach. However, no standard guidelines or manuals in consolidated form are available for its various construction activities. I compliment the Construction Management team for bringing out these manuals wherein the main focus of the authors has been to combine the theoretical & practical aspects drawn from their respective experience in transmission lines construction, academic institutions and industry. An attempt has been made to explain the fundamentals in a simple & lucid language. I am convinced that these manuals will act as guidelines and serve the needs of our practicing Managers & site Engineers. I should be our endeavour to follow these systems and procedures to enhance the quality of construction management in transmission and quality power. More such User’s Manuals covering the other related fields should be prepared for the benefit of the ultimate users at our remote sites as well as for the younger generation inducted in POWERGRID. (R.P. SINGH)
CONTENTS SECTION-I SOIL INVESTIGATION SL. NO. 1.0 1.1 1.2 1.2.1 1.2.2 1.3 1.3.1 1.3.2 1.3.3 1.3.4 1.3.5 1.3.6 1.3.7 1.4 1.4.1 1.5 1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7
DESCRIPTION INTRODUCTION PURPOSE OF SOIL INVESTIGATION TYPE OF TESTING BORING SHELL AND AUGER BORING SAMPLING GENERAL DISTURBED SAMPLE UNDISTURBED SAMPLE UNDISTURBED SAMPLING IN COHESIVE SOIL UNDISTURBED SAMPLING USING PISTON SAMPLER UNDISTURBED SAMPLING IN COHESIONLESS SOILS TYPES OF SAMPLERS INSITU PERMEABILITY TEST PUMP-IN TEST STANDARD PENETRATION TEST STATIC CONE PENETRATION TEST DYNAMIC CONE PENETRATION TEST VANE SHEAR TEST PLATE LOAD TEST TRIAL PIT GROUND WATER ELECTRICAL RESISTIVITY TEST FIELD INVESTIGATION ROCK LABORATORY TESTING REPORT RATES & MEASUREMENTS SPECIFIC REQUIREMENTS FOR GEOTECHNICAL
PAGE NO. 1 1 3 3 3 4 4 4 5 6 6 7 7 7 8 9 11 12 12 13 15 18 19 20 24 29 37 39
2.8
INVESTIGATION AT RIVER CROSSINGS SUMMARY OF RESULTS OF LABORATORY TEST ON
40
2.9 3.0
SOIL AND WATER SAMPLES TOOLS AND PLANTS FOR SOIL INVESTIGATIONS GUIDELINES FOR CONDUCTING SOIL INVESTIGATION
42 44
IN TRANSMISSION LINE
SECTION-II TOWER FOUNDATIONS CHAPTER-1 GENERAL SL. NO. 1.0 1.1 1.2 1.3 1.4
DESCRIPTION TOWER FOUNDATIONS LOADS, SAFETY FACTORS AND SETTLEMENT CLASSIFICATION OF SOILS PROPERTIES OF SOILS DATA FOR FOUNDATION DESIGN
PAGE NO.
CHAPTER-2 TYPES OF FOUNDATIONS SL. NO. 2.0 2.1
DESCRIPTION INTRODUCTION TYPES OF FOUNDATION
PAGE NO.
CHAPTER-3 CLASSIFICATION AND STUB SETTING SL. NO. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10
DESCRIPTION LINE CONSTRUCTION INVESTIGATION AND SURVEY TRANSPORTATION FOUNDATION PREPARATION OF FOUNDATION SITE TYPE OF FOUNDATION TO BE ADOPTED PIT MARKING SHORING AND SHUTTERING DEWATERING EXCAVATION IN ROCK PROCEDURE FOR SETTING STUBS OF
PAGE NO.
SITE
BY
COMBINED STUB SETTING
CHAPTER-4 TYPES OF FOUNDATIONS SL. NO. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8
DESCRIPTION CONCRETE TYPE MIXES SIZES OF AGGREGATES GRAVEL SUB-BASE REINFORCEMENT FORM WORK MIXING, PLACING AND COMPACTING OF CONCRETE BACK FILLING CURING
PAGE NO.
CHAPTER-5 PROTECTION OF FOUNDATION SL. NO. 5.0 5.1
DESCRIPTION CONCRETE TYPE UPLIFT RESISTANCE
PAGE NO.
5.2 5.3 5.4
REVETMENT BENCHING PROTECTION OF FOUNDATION AGAINST CHEMICAL
5.5
WATER MEASUREMENT OF VOLUME FOR REVETMENT AND BENCHING
CHAPTER-6 CONCRETE TECHNOLOGY SL. NO. 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12
DESCRIPTION INTRODUCTION PROPORTIONING CONCRETE MIXTURES FRESH CONCRETE HANDING AND BATCHING CONCRETE MATERIALS BATCH PLANTS AND MIXERS READY MIXED CONCRETE MOVING AND PLACING CONCRETE CONSOLIDATING CONCRETE RECOMMENDED VIBRATION PRACTICES FINISHING AND CURING CONCRETE PLACING CONCRETE IN COLD WEATHER PLACING CONCRETE IN HOT WEATHER
PAGE NO.
CHAPTER-7 MECHANISED CONSTRUCTION SL. NO. 7.0 7.1
DESCRIPTION INTRODUCTION MECHANICAL CONSTRUCTION EQUIPMENT & THEIR
7.2 7.3 7.4 7.5 7.6 7.7 7.8
APPLICATIONS WORK STUDY ON CONSTRUCTION EQUIPMENT PLANT PURCHASE VERSUS PLANT HIRE SAFETY PROGRAMME WHY MECHANICAL CONSTRUCTION EQUIPMENT? PRODUCTION OUT PUTS PRODUCTION TRIAL ECONOMIC LIFE
PAGE NO.
CHAPTER-8 STANDARD FIELD QUALITY PLAN SL. NO.
DESCRIPTION
PAGE NO.
8.0
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES
CHAPTER-9 GUIDELINES SL. NO. 9.0 9.1 9.2 9.3
DESCRIPTION PIT MARKING STUB SETTING CONSTRUCTION MATERIALS INSTALLATION OF REINFORCEMENT STEEL & FORM
9.4
BOXES MIXING, PLACING AND COMPACTING OF CONCRETE
PAGE NO.
CHAPTER-10 CHECK FORMAT SL. NO. 1.0 2.0 3.0 4.0 5.0
DESCRIPTION CHECK FORMAT FOR PIT MARKING CHECK FORMAT FOR FOUNDATION CLASSIFICATION CHECK FORMAT FOR STUB SETTING CHECK FORMAT FOR CONSTRUCTION MATERIALS CHECK FORMAT FOR INSTALLATION OF
6.0
REINFORCEMENT STEEL & FORM BOXES CHECK FORMAT FOR MIXING, PLACING
AND
COMPACTING OF CONCRETE ANNEXURE-IA : TOOLS & PLANTS FOR EXCAVATION, STUB SETTING AND CONCRETING ANNEXURE-IB : MANPOWER FOR EXCAVATION, STUB SETTING & CONCRETING GANG ANNEXURE-IC : REINFORCED CONCRETE RETAINING WALLS
PAGE NO.
SECTION-1 Soil Investigation
___________________________________________________________________________ SECTION ONE ___________________________________________________________________________ SOIL INVESTIGATION Back to contents page 1.0
INTRODUCTION Back to contents page An investigation of sill is essential for judging its suitability for the proposed engineering works and for preparing adequate and economic design. In general, the purpose of soil investigation is to obtain necessary information about the soil and to know the engineering properties of soil which will be affected. Earlier, the soil investigation of locations of transmission line towers was not very popular and general practice had been to adopt 4to 5 types of standard design foundations for different classes of soils encountered. Only special foundations in river beds necessitating huge volumes of concrete were investigated for properties of soils. Now the soil investigation of normal foundations is also felt necessary in good number of locations in the 400 kv transmission lines which helps in better choice of standard foundation & development of new designs to achieve overall cost, economy and minimise chances of failure.
1.1
Purpose of soil investigation: Back to contents page a)
Technical Consideration
b)
Economic Consideration
a)
Technical Considerations : An inadequate design or a conservative choice of standard foundation can lead to a failure causing long outage of transmission line. In modern practice, a large variety of standardised foundations are being pre-designed with different sets of properties attached to forseeably encountered soils. Aarge varity of soils are encountered as length of transmission lines are increasing with voltage llevels going up. To obtain optimal choice of pre-designed standard foundations,it is very much necessary to have a proper scientific knowledgfe of properties of soil against the back-drop of increasing sizes of towers, foundations, loads, thereby minimising the risk of failures of foundations.
b)
Economic Considerations : Among site erection activities, the foundations form the major chunk of the cost. The cost of foundations constitures 50 to 70% of the toral cost of erection depending upon terrain conditions. It forms 10 to 15% of the total cost of transmission line. A considerable saving in the foundation cost can be achieved by having detailed knowledge of soil properties and making wide usage of them in designing the foundations in sufficient types and classification of the foundations in field to match the most optimum size and type of foundation.
1.2
Types of Testing : Back to contents page
1.2.1
Boring :
Bore holes are generally taken at specified locations to obtain
information about the sub soil profile, its nature and strength and to collect soil
samples for strata identification and conducting laboratory tests. The minimum diameter of the bore hole shall be 150 mm and boring shall be carried out in accordance with the provision of IS:1892. Casing pipe is used in the bore hole to support its side when a side fall is suspected to occur inside the borehole. When casing pipe is used, it shall be ensured that its bottom end is at all times less than 15cms above the bottom of the borehole and not below the level at which the test has to be conducted or sampling has to be done. In case of cohesion less soils the advancement of the casing pipe shall be such that it does not disturb the soil to be tested or sampled. The casing shall be advanced by slowly turning the casing pipe and not by driving. 1.2.2
Shell and Auger Boring: Cylindrical augers and shells with cutting edge on teeth at the lower end can be used for making deep boring. Hand operated rings are used for depths up to about 25m and the mechanized rings up to 50m. Shell and auger boring can be used in all types of soil free from boulders. For cohesion less soil below ground water table, the water table in the borehole shall always be maintained at or above the ground water level. The use of chisel bit is permitted in hard strate with SPT-N value greater than 100.Chisel bits are also used to extend the borehole through local obstructions such as old construction boulders, rocky formation etc. The various activities to be conducted during the boring include standard penetration test, collection of undisturbed and disturbed samples of soil at various depths, logging of different layers of soil, depth of subsoil water and preparation of data sheets. Further a series of tests have to be conducted on the disturbed and undisturbed samples of soil at laboratory. Back to contents page
1.3
Sampling : Back to contents page
1.3.1
General : Back to contents page (a)
Sufficient number of soil samples shall be collected. Disturbed soil samples shall be collected for field identification and conducting tests such as sieve analysis, index properties, specific gravity, chemical analysis etc. Undisturbed sample shall be collected to estimate the physical strength and settlement properties of the soil. All the accessories required for sampling and the method of sampling shall confirm to IS:2132.
(b)
All the samples shall be identified with date, bore hole and trial pit number, depth f sampling etc. It is also essential to mark and arrow pointing towards the top surface of the sample as the soil was in-situ. Care shall be taken to keep the core samples and box samples vertically with the arrow directing upwards . The tube samples shall be properly trimmed at one end and suitably caped and sealed with molten paraffin wax.
1.3.2
Disturbed Sample Back to contents page a) Disturbed soil samples shall be collected in bore holes at regular itervals.Jar samples weighing approximately 10N shall be collected in boreholes at 0.5m intervals starting from a depth of 0.5 m below ground level and at every identifiable change of strata to supplement the boring
records. Samples shall be immediately stored in air tight jars and shall fill the jar as far as possible. b)
In elevated areas, if superficial material is available in plenty, then bulk samples from a depth of about 0.5m below ground level shall be collected to establish all the required properties to use it as a fill material. Disturbed samples weighing about 250 N shall be collected at shallow depths and immediately stored in polythene bags as per IS:1892. The bags shall be sealed properly to avoid any change in moisture content and they shall be kept in wooden boxes.
1.3.3
Undisturbed Sample : Back to contents page In each borehole undisturbed sample shall be collected at every change of strata and depths of 1.0 4.0 7.0,10.013.0,15.5m and water at regular intervals of 3.0m and as directed by the Engineer. The depth interval between the top levels of undisturbed sampling and standard penetration test shall not be less than 10.m. Undisturbed samples shall be of 100m dia and 450 mm length. Samples shall be collected in such a manner that the structure of the soil and its moisture content do not get asserted. The specifications for the accessories required for sampling and the sampling procedure shall conform to IS:1892 and IS:2132. Undisturbed sampling in sand shall be done using compressed air technique mentioned in IS:8763. Thin walled sampler shall be used to collect undisturbed samples by pushing the tube into the soil. The sampling tube shall have a smooth finish on both surfaces and minimum effective length of 450mm. The area ratio of sampling tubes shall be less than 12.5%. However, in case of very stiff soils, area ratio up to 20% shall be permitted. Area ratio
should be as low as possible. In no case it should be greater than 25%. The inside clearance of the sampler should lie between 1 to 3 percent and the outside clearance should not be much greater than the inside clearance. 1.3.4
Undisturbed Sampling in Cohesive Soil Back to contents page Undisturbed samples in soft to stiff cohesive soils shall be obtained using a thin walled sampler. In order to reduce the wall friction, suitable precautions such as oiling the surfaces shall be taken.
1.3.5
Undisturbed Sampling using Piston Sampler Back to contents page Undisturbed samples in very loose saturated sandy and silty soils and very soft clays shall be obtained by using a piston system. In soft clays and silty clays, with water standing in the casing pipe, piston sampler shall be used to collect undisturbed samples. During this method of sampling expert supervision is called for. Accurate measurement of the depth of sampling, height of sampler, stroke and length of sample recovery shall be recorded. After the sampler is pushed to the required depth, both the sampler cylinder and piston system shall be drawn up together ensuring that there shall not be any disturbance to the sample which shall then be protected from changes in moisture content.
1.3.6
Undisturbed Sampling in Cohesion less Soils Back to contents page Undisturbed samples in cohesionless soils shall be obtained as per the procedure given in IS:8763. Compressed air sampler shall be used to take samples of cohesionless soils below water table.
1.3.7
Type of Samplers: Back to contents page Samplers which shall be used commonly at sites are open drive sampler, stationary piston sampler, and Rotary samplers depending upon the mode of operation. Open drive types can be both the thick and thin wall samplers and the stationary piston and the rotary types are thin wall sampler - depending upon the area ratio (Fig.1 & Fig.2) Area ratio
Inside Clearance
D22 - D12 = ------------------- X 100 Percent D12 =
D3 - D1 ---------------- X 100 percent D1
D2 - D4 Outside Clearance = ---------------- X 100 percent D4 1.4
In situ permeability test : In situ permeability test shall be conducted to determine the water percolation capacity of overburden soil. The specification for the equipments required for the test and the procedure of testing shall be in accordance with IS: 5529, part -1. When it is required to carry out the permeability test for a particular section of the soil strata above the ground water table, bentonite slurry shall not be used while boring. Back to contents page
1.4.1
Pump-in test: Back to contents page
Pump-in test shall be conducted in the bore hole/trial pit by allowing water to percolate into the soil. Choice of the method of testing shall depend on the soil permeability and prevailing ground water level. a)
Constant Head Method ( in bore hole): This test shall be conducted in boreholes where soils have a high permeability i.e. it shall be allowed into the borehole through a metering system ensuring gravity flow at constant head so as to maintain a steady water level in the borehole. A reference mark shall be made at a convenient level which can be easily seen in the casing pipe to note down the fluctuations of water level. The fluctuation shall be counteracted by varying the quantity of water flowing into the borehole. The elevation of water shall be observed at every 5 minute interval. When three consecutive readings show constant value, the necessary observations such as flow rate, elevation of water surface above test depth, diameter of casing pipe etc. Shall be made and recorded as per the proforma recommended in IS:5529, PART-I, Appendix-A.
b)
Falling head method ( in bore hole) This method shall ve adopted for relatively less permeable soils where the discharge is small and where the soil can stand without casing. The test section shall be seated by the bottom of the borehole and a packer at the top of the test section. If the test has to be conducted at an intermediate section of a prebored hole then, double packer shall be used . Access to the test section through the packer shall be by means of a pipe which shall extend to above the ground level. Water shall be
filled into the pipe upto the level marked just below the top of the pipe and water allowed to drain into the test section. The water level in the pipe shall be recorded at regular intervals as mentioned in IS:5229,part-I, Appendix- B. The test shall be repeated till constant records of water level are achieved. 1.5 Standard penetration Test : Back to contents page The test shall be performed in a clean hole, 55 to 150 mm in diameter. A casing or drilling mud shall be used to support the sides of the hole. The test shall be conducted at depth of 2.0, 3.0, 5.0, 6.0, 8.0, 9.0, 11.0, 12.0, 14.0, m and at 3.0m intervals and every change of strata and as per the direction of the Engineer-in-charge. A standard thick wall split-tube sampler, 50.8 mm shall be driven into the undisturbed soil at the bottom of the hole under the blows of a 65 kg drive weight with 75 cm free fall. The minimum open length of the sampler should be 60 cm. The sampler shall be first driven through 15 cm as a seating drive. It shall be further driven through 30cm or until 100 blows are applied. The number of blows required to give the sampler 30 cm beyond the seating drive, is termed as penetration resistance N. This test shall be discontinued when the blow count is equal to 100 or the penetration is less than2.5 cm for 50 blows whichever is earlier. At the location were the test is discontinued the penetration and the number of blows shall be reported. Sufficient quantity of disturbed soil samples shall be collected from the split spoon sampler for identification and laboratory testing. Following Tables give some of the empirical correlation of the soil properties with the penetration resistance corrected for depth and for fine saturated sand.
Table (1)
Penetraqtion resistance and Empirical correlations for cohesionless soils.
Penetration Resistance N (Blows)
Approx. (Degrees)
Density Index (%)
Description
-
25-30
0
Very Loose
Approx. Moist Density (t/m2) 1.12-1.6
4
27-32
15
Loose
1.44-1.84
10
30-35
35
Medium
1.76 –2.08
30
35-40
65
Dense
1.76 –2.24
50
38-43
85
Very dense
2.08 –2.40
Table (2) :
1.6
Penetration resistance and empirical correlations for cohesive soils
Penetration Resistance N (blows)
Unconfined Compressive Strength (t/m2)
Saturated Density (t/m3)
Consistency
0
0
-
Very soft
2
2.5
1.6 - 1.92
Soft
4
5
1.76 -2.08
Medium
8
10
-
Stiff
16
20
1.92 - 2.24
Very stiff
32
40
-
Hard
Static cone penetration test : Static cone penetration test shall be conducted to know the soil stratification and to estimate the various soil propertie such as density, undrained shear strength etc. The cone penetrometer shall be advanced by pushing and the static forcr required for unit penetration shall be determined. The test shall be conducted upto the specified depth or refusal whichever is earlier. For this test ‘refusal’ means meeting a very hard strata which can’t be penetrated at the rate of at least 0.3cm/sec even when the
equipment is loaded to its full capacity. The specifications for the equipment and accessories required for performing the test, test procedure, field observations and reporting of results shall conform to 1S: 4968, Part 111. Only 100 kN capacity mechanically operated equipment shall be used. At the ground level, preboring upto 0.5 m depth shall be permitted if the overlying strata is hard. Continuous record of the penetration resistance shall be maintained. Back to contents page 1.7 Dynamic cone penetration test: Dynamic cone penetration test shall be conducted to predict stratification, density, bearing capacity etc of soils. The test shall be conducted upto the specified depth or refusal whichever is earlier. Refusal shall be considered when the blow count exceeds 150 for 300mm penetration. The specification for the equipment and accessories re- quired for performing this test, test procedure, field observations and reporting of results shall conform to 18:4968 Part-ll. The driving system shall comprise of a 650 weight having a free fall of 0.75m. The cone shall be of 65 mm diameter provided with vents for'continuous flow of bentonite slurry through the cone and rods in order to avoid friction between the rods & soil. On completion of the test, the result shall be presented as a continuous record of the number of blows required for every 300mm penetration of the cone into the soil in a suitable chart supplemented by a graphical plot of blow count for 300 mm penetration vs. depth. Back to contents page 1.8
Vane shear test: Field vane shear test shall be performed inside the borehole to determine the undrained shear strength of cohesive soil -especially of soft and sensitive clays, which are highly susceptible to sampling disturbance. The vane shear test consist of four thin steel plates called vanes, welded
orthogonally to a steel rod (Fig.3) .The test shall be conducted by advancing this four winged vane of s~itable size (as per the soil condition) into the soil upto the desired depth and measuring the torque required to rotate the vane. The torque shall be measured through a torque measuring arrangements such as calibrated torsion spring, is attached to the steel rod which is rotated by a worm gear and worm wheel arrangement. The specification for the equipments and accessories required for conducting the test, the test procedure and field observations shall correspond to IS: 4434. Tests mayalso be conducted by direct penetration from ground surface. On completion of the test the results shall be reported in an approved proforma as specified in IS: 4434, AppendixA. Back to contents page 1.9
Plate Load Test: Plate load test shall be conducted to determine the ultimate bearing capacity of soil, and the load/settlement characteristics of soil at shallow depths by loading a plane and leveled steel plate kept at the desired depth and measuring the settlement under different loads, until a desired settlement takes place or failure occurs. The specification for the equipment and accessories required for conducting the test, the test procedure, field observations and reporting of results shall conform to IS:1888. The test pit shall be made five times the width of the plate. At the centre of the pit, a small square hole shall be dug whose size shall be equal to the size of the plate and the bottom level of which correspond to the level of actual foundation (Fig.4) .
The loading to the test plate shall be applied with the help of a hydraulic jack. The reaction of the hydraulic jack shall be borne by either of the following two methods: a) Gravity loading platform method b) Reaction truss method. In case of gravity loading method a platform shall be constructed over a vertical column resting on the test plate and the loading shall be done with the help of sand bags, stones or concrete blocks. The general arrangement of the set up for this method is shown in Fig. 5 & 6. If the water table is at a depth higher than the specified test depth, the groundwater shall be lowered and maintained at the test depth for the entire duration of the test. 1.9.1
A seating load of 70 gm/sq.cm shall be applied and after the dial gauge readings are stabilized , the load shall be released and the initial readings of the dial gauges recorded after they indicate constant reading. The load shall be increased in stages. These stages shall be 20, 40, 70, 100, 150, 200, 250, 300, 400, 500, 600 and 800 KN per sq.m. or as directed by the Engineer. Under each loading stage, record of Time vs Settlement shall be kept as specified in IS: 1888. The load shall be maintained for a minimum duration of one hour or till the settlement rate reduces to 0.02 mm/ min whichever is later. No extrapolation of settlement rate from periods less than one hour shall be permitted.
1.9.2
Loading shall be carried out in stages as specified above till one of the following conditions occurs. a)
Failure of the soil under the plate i.e. the settlement of the plate at constant load becomes progressive and reaches a value of 40 mm or more.
1.9.3
Dial
b)
Total settlement of the plate is more than 40 mm.
c)
Load intensity of 800 KN/Sq.m is reached without failure of the soil.
gauge
readings
for
settlement
shall
generally
be
taken
at
1,2.25,4,6.25,9,16,25,60,90 and 120 minutes from the commencement of each stage of loading. Thereafter the readings shall be taken at hourly intervals upto a further 4 hours and at two hours intervals thereafter for another 6 hours . 2.0
Trial pit Back to contents page
2.0.1
Trial pits shall be of minimum 2mx2m size at the bottom so as to permit easy access for visual examination of walls of the pit and to facilitate sampling and insitu testing operations. pits shall be upto 4 m deep or as per the directions of the Engineer. Precautions shall be taken to ensure the stability of pit walls including provision of shoring, if necessary, as per IS: 4453: Precautions shall be taken to prevent surface water draining into the pit. Arrangements shall be made for dewatering if the pit is extended below water table. Trial pits shall be kept dry and a ladder shall be provided for easy access to the bottom of the pit. In-situ tests shall be conducted and undisturbed samples shall be collected immediately on reaching the specified depth so as to avoid substantial changes in moisture content of the subsoil. Arrangements shall
be made for barriers, protective measures and lighting necessary for the period the pits remain open. 2.0.2
A note on the visual examination of soil strata shall be prepared. This should include the nature, colour, consistency and visual classification of the soil, thickness of soil strata, groundwater table, if any, etc.
2.0.3
Undisturbed samples shall be collected at 1.0, 2.0, 3.0 m depth and at the termination depth in all the pits. a) Chunk Samples In cohesive soils, undisturbed samples of regular shapes shall be collected. The samples shall be cut and trimmed to a suitable size (0.3x0.3x0.3m). A square area (0.35x0.35m) shall be marked at the centre of the leveled surface at the bottom of the pit. Without disturbing the soil inside the marked area, the soil around this marking shall be carefully removed upto a depth of 0.3Sm. The four vertical faces of the soil block protruding at the centre to be trimmed slowly so that its size reduces to 0.3mx0.3m. Wax paper cut to suitable size shall be wrapped uniformly covered with two layers of thin cloth over all the S exposed surfaces of the soil block and sealed properly using molten wax. A firmly constructed wooden box of size 0.3Sx0.35x0.35m (internal dimensions) with the top and bottom open shall be placed around the soil block and held such that its top edge protrudes just above the surface of the block. The space between the soil block and the box shall be filled uniformly and tightly with moist sawdust. The top surface shall also be covered with saw dust before nailing the wooden lid to cover the box firmly taking care that the soil block is not
disturbed. The area of contact between the bottom portion of the block and the ground shall be reduced slowly by removing soil in small quantities using small rods, so that the block can be separated from the ground slowly without disturbance. After inverting the wooden box along with the soil block, the bottom portion shall be trimmed and covered with wax paper, cloth and sealed with molten wax. A wooden lid shall be nailed to the box after providing proper saw dust cushion below it. An arrow mark shall be made on the vertical face of the wooden box to indicate the top surface along wi th the coordinates and depth of sampling . b) Tube Samples Undisturbed tube samples may also be obtained by means of a l00mm diameter sampling tube with a cutting edge. The sampler shall be slightly oiled or greased inside and outside to reduce friction. The sampler shall be pushed into the soil and while doing so, soil around the tube shall be carefully removed. In case it is not possible to push the sample, it may be driven by light blows from a "monkey". 2.0.4
In each trial pit the soil in-situ density shall be determined by the sand replacement method. The specifications, equipments, accessories required for the test and test procedure shall be as per IS: 2720, Part- XXVIII. No separate payment shall be made for this test.
2.1
Ground Water Back to contents page
2.1.1
One of the following methods shall be adopted for determining the ground water table in bore holes as per IS: 693 5 and as per the lnstructions of the Engineer. a)
In permeable soils, the water level in the hole shall be allowed to stablise after depressing it adequately by bailing. When the water level inside the bore hole is found to be stable, the depth of water level below ground level shall be measured. Stability of sides and bottom of the bore hole shall be ensured at all times.
b)
For both permeable and impermeable soils, the [following method shall be suitable. The bore hole shall be filled with water and then bailed out to various depths. Observations on the rise or fall of water level shall be made at each depth. The level at which neither a fall nor a rise is observed shall be considered as the water table elevation. This shall be established by three successive readings of water level taken at an interval of two hours.
2.1.2
In case any variation in the groundwater level is observed in any specific boreholes, then the water level in these I boreholes shall be recorded daily during the course of the field investigation. Levels in nearby wells, streams, etc., if any, shall also be noted whenever these readings are taken.
2.1.3
Sub-soil Water Samples a)
Sub-soil water samples shall be collected for carrying out chemical analysis thereon. Representative samples of groundwater shall be collected when it is first encountered in bore holes before the addition of water to aid boring or drilling.
b)
Chemical analysis of water samples shall include determination of pH value; turbidity, sulphate, carbonate, nitrate and chloride contents; presence of organic matter and suspended solids. Chemical preservatives maybe added to the sample for cases as specified in'the test method/IS codes. This shall only be done if analysis cannot be conducted within an hour of collection and shall have the prior written permission and approval of the Engineer.
2.2
Electrical Resistivity Test Back to contents page This test shall be conducted to determine the Electrical resistivity of soil required for designing safety grounding system for the entire switch yard area. The specifications for the equipments and other accessories required for performing electrical resistivity test, the test procedure, and reporting of field observations shall conform to 1S:3043. The test shall be conducted using Wanner's four electrode method as specified in 1S:1892,AppendixB2.Unlessotherwisespecified, at each test location, the test shall be conducted along two perpendicular lines parallel to the coordinate axes. On each line a minimum of 8 to 10 readings shall be taken by changing the spacing of the electrodes from an initial small value of 0.5m upto a distance of 10.0m.
2.3 Field Investigation Rock Back to contents page 2.3.1
Rock Drilling a)
Boring shall be continued in large hard fragments or natural rock beds like but not limited to igneous, sedimentary and metamorphic formations. The equipments, method and the procedure for drilling
operation shall conform to IS:1892. The starting depth of drilling in rock shall be certified by the Engineer. The portion drilled in rock shall be backfilled with cement and sand (1:3) grout. b)
Drilling shall be carried out with NX size tungston carbide (TC) or diamond tipped drill bits depending on the type of rock and as per IS:6926. Suitable type of drill bit (TC/Diamond) and core catchers shall be used to ensure continuous and good core recovery. Core barrels and core catchers shall be used for breaking off the core and retaining i t when the rods are withdrawn. Double tube core barrels shall be used to ensure better core recovery and to pick up cores from layers of bed rock. Water shall be circulated continuously down the hollow rods and the sludge conveying the rock cuttings to the surface shall be collected. A very high recovery ratio shall be aimed at in order to get a satisfactory undisturbed sample. Core of minimum 1.5m length shall be aimed at. Normally TC bit shall be used. Change over to a diamond bit shall require the specific written approval of the Engineer and his decision whether a TC or a diamond bit is to be used shall be final and binding on the Contractor.
c)
No drilling run shall exceed 1.5m in length. If the core recovery is less than 80% in any run the length of the subsequent run shall be reduced to 0.75m. During drilling operations observations on return water, rate of penetration, etc., shall be made and recorded as per IS:5313. i)
The colour of return water at regular intervals, the depth at which any change of colour of return water is observed, the
depth of occurrence and amount of flow of hot water, if encountered, shall be recorded. ii)
The depth through which a uniform rate of penetration was maintained, the depth at which marked change in rate of penetration or sudden fall of drill rod occurs the depth at which any blockage of drill bit causing core loss, if any, shall be recorded.
iii)
Any heavy vibration or torque noticed during drilling should be recorded together with the depth of occurrence.
iv)
Special conditions like the depth at which grouting was done during drilling fluid, observation of gas discharge with return water etc., shall also be observed and recorded.
v)
All the observations and other details shall be recorded as a daily drill and reported in a proforma as given in IS:5313.
d)
Core samples shall be extracted by the application of a continuous pressure at one end of the core with the barrel held horizontally without vibration. Friable cores shall be extracted from the barrel directly into a suitable sized half round plastic channel section. Care shall be taken to maintain the direction of extrusion of sample same as while coring to avoid stress reversal.
e)
Immediately after withdrawl from the core barrel, the cores shall be placed in a tray and transferred to boxes specially prepared for the purpose. The boxes shall be made from seasoned timber or any other durable material and shall be indexed on top of the lid as per IS : 4078. The cores shall be numbered serially and arranged in the boxes in a
sequential order. The description of the core samples shall be recorded as per IS : 4464. Where no core is recovered, it shall be recorded as specified in the standard. Continuous record of core recovery and RQD to be mentioned in the corelog as per IS : 11315 Part-II. 2.3.2
Permeability Test Permeability Test shall be conducted in bedrock inside the drilled holes by pumping in water under pressure to determine the percolation capacity of the rock strata. This test shall be conducted in uncased and ungrouted sections of the drill hole and the use of bentonite slurry during drilling is strictly prohibited when this test has to be conducted. Clear and clean water shall be used for the purpose of both drilling and testing. The equipments required and the procedure to be followed for conducting the test shall conform to IS : 5529, Part-II. The length of the test section shall be either 1.5m or 3.0 m as per field conditions and the directions of the Engineer. The level of water table, if any, in the drill hole shall be recorded and the drill hole shall be cleaned before beginning the test. Depending upon the depth of the test section, single packer or double packer method shall be adopted. Care shall be taken to see that all joints and connections are watertight during the test. a)
Single Packer Method This method shall be adopted when the bottom elevation of the test section is the same as the bottom of the drill hole and where it is considered necessary to know the permeability values during drilling itself. This test shall be useful where the full length of the hoe cannot stand uncased or ungrouted. The packer shall be fixed at the top level
of test section such that only the test section lies below the packer. Water shall then be pumped through a pipe into the test section under a particular pressure and maintaining it till a constant quantity of water intake is observed. The amount of water percolating through the hole shall be recorded at every 5 mm intervals. The test shall be repeated by increasing the pressure at regular intervals upto a pressure limit as specified in IS : 5529, Part-II. The details and observations during the test shall be suitably recorded in a proforma recommended in IS : 5529, Part-II, Appendix-B. b)
Double Packer Method This method shall be used when the permeability of an isolated section inside a drill hole has to be determined. Packers shall be fixed both at the top and bottom of the test section such that their spacing is exactly equal to the length of the test section.
2.4 Laboratory Testing Back to contents page 2.4.1
Essential Requirements a) Depending on the type of sub strata encountered, appropriate laboratory tests shall be conducted on soil and rock samples collected in the field. Laboratory tests shall be scheduled and performed by qualified and experienced personnel who are thoroughly conversant with the work. Tests indicated in the schedule of items shall be performed on soil, water and rock samples as per relevant IS: codes. One copy of all the laboratory test data records shall be submitted to the Powergrid progressively every week. Laboratory tests shall be carried out concurrently with field investigation
since initial laboratory test results could be useful in planning the later stages of fieldwork. A schedule of laboratory tests shall be established by the Contractor to the satisfaction of the Engineer within one week of completion of the first borehole. b)
Laboratory tests shall be conducted using approved apparatus comply in with the requirements and specifications of/'Indian Standards or other approved standards for this class of work. It shall be checked that the apparatus are in good working condition before starting the laboratory tests./Calibration of all the instruments and their accessories shall be done carefully and precisely. The tests shall be conducted at an approved laboratory.
c)
All samples, whether undisturbed or disturbed, shall be extracted, prepared and examined by competent personnel properly trained and experienced in soil sampling, examination, testing and in using the apparatus as per the specified standards.
d)
Undisturbed soil samples retained in lines or seamless tube /samplers shall be taken out without causing any disturbance to the samples using suitably designed extruders just prior to actual testing. If the extruder is horizontal, proper support shall be provided to prevent the sample from breaking. For screw type extruders, the pushing head shall be free from the screw shaft so that no torque is app11ed to the soil sample in contact with the pushing head. For soft clay samples, the sample tube shall be cut by mean of a high speed hacksaw to proper test length and placed over the mould before pushing the sample into it with a suitable piston.
e)
While extracting a sample from a liner or tube, care shall be taken to see that its direction of movement is the same as that during sampling to avoid stress reversal.
2.4.2
Tests Tests as indicated in this specification and as called for by the Engineer shall be conducted. These tests shall include but not be limited to the following. a)
Tests on Undisturbed and Disturbed Samples
-
Visual and Engineering Classification
-
Sieve Analysis and Hydrometer Analysis
-
Liquid, Plastic and Shrinkage Limits
-
Specific Gravity
-
Chemical Analysis
-
Swell Pressure and Free Swell index determination
-
Proctor Compaction test
-
California Bearing Ratio
b)
Tests on Undisturbed Samples
-
Bulk Density and Moisture Content
-
Relative Density (for sand)
-
Unconfined Compression Test
-
Box Shear Test (in case of sand)
-
Triaxial Shear Tests: (depending on the type of soil and field conditions on undisturbed or remoulded samples ) i)
Unconsolidated undrained,
ii)
Consolidated Undrained Test with the Measurement of Pore Water Pressure.
iii) -
Consolidated Drained.
Consolidation
c)
Tests on Rock Samples
-
Visual Classification
-
Moisture Content, Porosity and Density Specific Gravity Hardness
-
Slake durability
-
Unconfined Compression test (both saturated and at insitu water content ) -Point load strength index
2.4.3
-
Deformability test (both saturated and dry, samples)
d)
Chemical Analysis of Sub soil water
Salient Test Requirements a)
Remoulded soil specimen, whenever desired, shall be fully reworked at field density and moisture content . For conducting CBR test and triaxial test for dyke and road material the sample shall be remoulded to 95% of standard proctor density.
b)
Triaxial shear test shall be conducted on undisturbed soil samples, saturated by the application of back pressure. Only if the water table is at sufficient depth so that chances of its rising to the base of the footing are meagre or nil, the triaxial tests shall be performed on specimens at natural moisture content. Each test shall be carried out on a set of three test specimens from one sample at cell pressures equal to 100, 200 and 300 KN/sq.m. or as required depending on the soil conditions .
c)
Effective stress triaxial shear test could be either consolidated drained or consolidated undrained with pore water pressure measurement. The test shall be conducted at cell pressure of 100,200 and 300 KN/ sqm.
increased in stages of 50 KN/sqm. ensuring complete consolidation at each stage. d)
Direct shear test shall be conducted on undisturbed soil samples. The three normal vertical stresses for each test shall be l00, 200 and 300 KN/sq.m. or as required as per the soil conditions .
e)
Consolidation test shall have loading stages of 10, 25,50,75,100,200, 400and800KN/Sq.m. Rebound curve shall be recorded for all the samples by unloading the specimen at the in-situ stress of the specimen. Additional rebound curves shall also be recorded whenever desired by the Engineer.
f)
Chemical analysis of sub-soil shall include determination of pH value; carbonate, sulphate (both SO3andSO4) , chloride and nitrate contents; organic matter; salinity and any other chemical harmful. to the foundation material. The contents in soils shall be indicated as percentage ( % ) .
g) Chemical analysis of sub-soil water sample shall include the determination of the properties such as colour, odour, turbidity, pH value and specific conductivity both at 25 deg.C and chemical contents such as Carborates, Surphates(both SO3 and SO4), Chlorides, Nitratesm Organic matter and any other chemical harmful to the founmdation material. The contents such as Sulphates, etc. shall be indicted as ppm by weight. h) The lab CBR test shall be performed on undisturbed and remoulded sample for soaked and unsoaked condition. 2.5 Report Back to contents page
2.5.1
General a)
On completion of all the field and laboratory work, the Contractor shall submit a formal report containing Geological information of the region, procedure adopted for investigation, field observations, summarised test data, conclusion and recommendations. The report shall include detailed borelogs, subsoil sections, field test results, laboratory observations and test results both in tabular as well as graphical form, practical and theoritical considerations for the interpretation of test results, the supporting calculations for the conclusions drawn, etc. Initially, the Contractor shall submit three copies of the report in draft from for the Owner's review.
b)
The Contractor's qualified Geotechnical engineer shall visit the Owners Corporate office for a detailed discussion on the Owners comments on his draft report. During the discussions, it shall be decided as to the modifications that need to be done in the draft report. Thereafter the Contractor shall incorporate in his report the agreed modifications and after get ting the amended draft report approved, ten copies of the detailed final report shall be submitted alongwith one set of reproducibles of the graphs, tables, etc .
c)
The detailed final report based on field observations, in-situ and laboratory tests shall encompass theoretical as well as practical considerations for foundations for different types of structures envisaged in the area under investigation. The Contractor shall acquaint himself about the type of structures, foundation loads and other information required from the Engineer.
2.5.2
Data to be Furnished The report shall also include but not be limited to the following : a)
A plot plan showing the locations and reduced levels of all field tests e.g. boreholes, trial pits, static cone penetration tests, dynamic cone penetration tests, plate load tests 1 etc. properly drawn to scale and dimensioned with reference to the established grid lines.
b)
A true cross section of all individual boreholes and trial pits with reduced levels and coordinates shown in the classification and thickness of individual stratum, position of ground water table, various in-situ tests conducted and samples collected at different depths and the rock stratum, if met with.
c)
A set of longitudinal and transverse soil/rock profiles connecting various boreholes in order to give a clear picture of the variation of the subsoil strata as per IS:6065.
d)
Geological information of the area such as geomorphology, geological structure, lithology, stratigraphy and tectonics, core recovery and rock quality designation, etc.
e)
Past observations and historical data, if available, for the area or for other areas with similar soil profile or with similar structures in the surrounding areas.
f)
Plot of Standard Penetration Test (N values both uncorrected and corrected) with depth for identified areas.
g)
Results of all laboratory tests summarised (i) for each sample (as per Table-I) as well as (ii) for each layer along with all the relevant charts,
tables, graphs, figures, supporting calculations, conclusitions and photographs of representative rock cores. h)
For all triaxial shear tests stress vs strain diagrams as well as Mohr’ s circle envelopes shall be furnished. If back pressure is applied for saturation, the magnitude of the same shall b~ indicated. The value of modulus of elasticity, E shall be furnished for all tests alongwith relevant calculations.
i)
For all consolidation tests, the following curves shall be furnished : e vs log p e vs p and Compression vs log t or Compression vs square root of t (depending upon the shape of the plot for proper determination of co-efficient of consolidation). The point showing the initial condition (eo, po) of the soil shall be marked on the curves.
j) The procedure adopted for calculating the compression index from the field curve and settlement of soil strata shall be clearly specified. The time required for 50% and 90% primary consolidation alongwith secondary settlements, if significant, shall also be calculated. k)
For pressuremeter tests, the following curves shall be furnished : Field pressure meter, creep and air calibration curves indicating Po' Pf and Pi. Corrected pressure meter and creep curves indicating Po, Pf', Pi alongwith calculation for the corrections.
l)
From the pressure-meter test results the values of cohesion, angle of internal friction, pressuremeter modulus, shear modulus and coefficient of subgrade reaction shall be furnished alongwith sample calculation. Calculation for allowable bearing pressures and corresponding total settlements, for shallow foundations and capacity calculation of piles in various modes shall also be included.
2.5.3
Recommendations Recommendations shall be given area wise duly considering the type of soil, structure and foundation in the area. The recommendations shall include but not be limited to the following : a)
Type of foundations to .adopt for various structures, duly considering the sub soil characteristics, water table, total settlements permissible for structures and equipments. Minimum depth and width of foundation shall also be recommended. The provision in relevant IS: Codes indicated in clause 4.0 shall be considered.
b) For shallow foundations the following shall be indicated with comprehensive supporting calculations. i)
Net safe allowable bearing pressure for isolated square footings and continuous strip footings of sizes 2.0,3.0 and 4.0m at three different founding depths of 1.0, 2. 0 and 4.0m below ground level considering both shear failure and settlement criteria, giving reasons for type of shear failure adopted in the calculation.
ii)
Net safe allowable bearing pressure for raft foundations of widths greater than 6m at 2.0m , 3.0m and 4.0m below ground level considering both shear failure and settlement criteria.
iii)
rate and magnitude of settlement expected of the structure.
iv)
Net safe bearing capacity for foundation sizes mentioned above, modulus of subgrade reaction, modulus of elasticity from plate load test results alongwith time settlement curves and load settlement curve in both natural and log graph, variation of Modulus of subgrade reaction with size, shape and depth of foundation.
c)
If piling is envisaged, the following shall be indicated with comprehensive supporting calculations: i)
Type of pile and reasons for recommending the same duly considering the soil characteristics.
ii)
Suitable founding strata for the pile.
iii)
Estimated length of pile for 500 KN (400 mm dia), 750 KN (450 mm dia), 1000 KN (500 mm dia) and 4500 KN (1070 mm dia) capacities. End bearing and frictional resistance shall be indicated separately.
iv)
Magnitude of negative skin friction, if any, to be considered in pile design.
2.5.4
Additional Recommendations a)
Coefficient of permeability of various sub soil and rock strata based on in-situ permeability tests.
b)
Cone resistance, frictional resistance, total resistance, relation between cone resistance and Standard Penetration Test N Value, and settlement analysis for different sizes of foundation as specified based on static cone penetration test.
c)
Electrical resistivity of sub-soil based electrical resistivity tests including electrode spacing vs cumulative resistivity curve.
d)
Suitability of the soil for construction of roads and pavements, their stable slopes for shallow and deep excavations, active and passive earth pressures at rest and modulus of elasticity as a function of depth for the design of underground structures.
e)
Suitability of locally available soils at site for filling and back filling purposes.
f)
If expansive soil is met with, recommendation on removal or retainment of the same under the foundation etc. shall be given. In the latter case, detailed specifications of any special treatment required including specifications for materials to be used, construction method, equipments to be deployed, etc. shall be furnished.
g)
Protective measures based on chemical nature of soil and ground water with due regard to potential deleterious effects on concrete, steel and other building materials, etc. Remedial measures for sulphate attack and acidity shall be dealt in detail. Susceptibility of soil to termite action and remedial measures for the same.
h)
Susceptibility of sub soil strata to liquifaction in the event of earthquake. If so, recommendation for remedial measures.
i)
Any other information of special significance like dewatering schemes, etc. which may have a bearing on the design and construction ,
j)
Recommendations for additional soil investigation beyond the scope of the present work if the Contractor considers such investigation is necessary.
2.6
Rates and Measurements Back to contents page The clauses below shall apply for item rate contracts only. They shall not be applicable to turn key and lumpsum contracts, except for work beyond the scope of such contracts.
2.6.1
Rates a)
The item of work in the Schedule of Quantities describes the work very briefly. The various items of the Schedule of Quantities shall be read in conjunction with the corresponding sections in the technical specifications including amendments and additions, if any. For each item in the Schedule of Quantities, the bidder's rates shall include for the activities covered in the description of the item as well as for all necessary operations in details described in this technical specification.
b)
The unit rates quoted shall include minor details which are obviously and fairly intended, and which may not have been included in these documents but are essential for the satisfactory completion of the work.
c)
The bidders quoted rates shall be inclusive of providing all plant equipments, men, materials, skilled and unskilled labour; making observations establishing the ground level and coordinates at location of each borehole, test pit, etc. by carrying levels from one established
bench mark and distances from one set of grid lines furnished by the Owner. Also, no extra payments shall be made for conducting the Standard Penetration Test; collecting, packing, transporting of all samples and cores; recording of all results and submitting them in approved formats. d)
No claims shall be entertained if the details are shown on the released for construction drawings differ in any way (e.g .location and depth for tests, number of tests, etc.) from those shown on the tender drawings.
2.6.2
Measurements a)
All measurements shall be in SI Units.
b)
Lengths shall be measured in meters (m) correct to two places of decimals. Areas shall be worked out in square meters (m2) and volume in cubic meters and which may not have been included in these documents but are essential for the satisfactory completion of the work.
c)
The bidders quoted rates shall be inclusive of providing all plant equipments, men, materials, skilled and unskilled labour; making observations establishing the ground level and coordinates at location of each borehole, test pit, etc. by carrying levels from one established bench mark and distances from one set of grid lines furnished by the Owner. Also, no extra payments shall be made for conducting the Standard Penetration Test; collecting, packing, transporting of all samples and cores; recording of all results and submitting them in approved formats.
d)
No claims shall be entertained if the details are shown on the released for construction drawings differ in any way (e.g. location and depth for tests, number of tests, etc.) from those shown on the tender drawings.
2.6.2
Measurements a)
All measurements shall be in SI Units
b)
Lengths shall be measured in meters (m) correct to two places of decimals. Areas shall be worked out in square meters (m2) and volume in cubic meters (m3), rounded off to two decimals.
c)
Certain tests have to be conducted in bore holes, trial pits, etc. Such boreholes, trial pits, etc., shall be measured only once and not again just because of a tests are conducted therein.
2.7
Specific Requirements for Geotechnica1 investigation at River Crossings Back to contents page The entire soil investigation work shall be carried ~ out in accordance with the relevant parts of the specification for geotechnical investigation. Standard Penetration test at River Crossings and special locations shall be carried out at the interval of 2.0, 3.0, 5.0, 7.0, 10.0 and thereafter at the rate of 3m intervals to 40m. However in each bore holes undisturbed samples shall be collected at every change of strata and at depths as follows: 1.0m, 4.0m, 7.0m, 11.0m and thereafter at the rate of 3m intervals up to 38m. The spacing between the top levels of undisturbed sampling and standard, penetration testing shall not be less than 1.0m. The boreholes shall generally be executed to, specified depth as per specifications or as shown in the drawing. If refusal strata is reached (i.e. SPT-N Value is greater than 100 continuously for 5m depth) the borehole may be terminated at shallower depth i.e. at 5m in refusal strata.
2.8
Summary of Results of Laboratory Tests on Soil and Water Samples
B
D
T
DENSITY
W
O
E
Y
(KN/Cu.m.)
A
R
P
P
E
T
E
H
H
O
Bulk
Dry
T
PARTICLE SIZE (%)
CONSISTANCY PROPERTIES
GRAVEL
SAND
SILT
CLAY
E R
O
L
(
E/
m
T
)
F
C O
S
N
RI
A
T
A
M
E
L
P
N
PI
L
T
T
E
(
N
%
O.
)
SOIL
L.L.
P.L.
P.I.
CLA
D
S
SSIF
E
P
ICA
S
E
TIO
C
C
N–
R
I
IS
I
F
P
I
T
C
I
G
O
R
N
A V I T Y
Notations : I. DB DP DS RM UB US W
For type of sample Disturbed Bulk Soil sample Disturbed SPT soil sample Disturbed Samples from cutting edge Of Undisturbed soil sample Remoulded soil sample Undisturbed soil sample Undisturbed Soil Sample by Sampler Water Sample
II. PMT SCPT UCC VST Tuu Tcu
For Strength Test Pressuremeter Test Static Cone Penetration Test Unconfined Compression Test Vane Shear Test Unconsolidated Undrained Triaxial Test Consolidated Undrained Triaxial Test with Pore Pressure Ted Consolidated Drained Triaxial Test (Note : 1. Replace T by D for Direct Shear Test)
STRENGTH TEST TYPE
C
III.
CONSOLIDATION TEST ec
pc
Cc
P
mv
Cv
For Others LL Liquid Limit (%) PL Plastic Limit (%) PI Plasticity Index (%) C Cohesion (KN/Sq.m.) Angle of Internal friction (degrees) S. Pr. Swelling Pressure (KN/Sq.m.) FSI Free Swell Index (%) ec Initial Void Ratio Pf Preconsolidation Pressure (KN/Sq.m.) Cc Compression Index P Pressure range (KN/Sq.m.) Mv Coefficient of volume compressibility (Sq.m./KN)
S H RI N K A G E LI M IT ( %)
SWELL TEST S. Pr
F S
COMPACTION TEST M.D.D.
O.M.C.
C.B.R.
Cv MDD OMC CBR IV.
Coefficient of consolidation (sq.m./hr) Maximum Dry Density (KN/Cu.m.) Optimum Moisture Content (%) California Bearing Ratio (%) For Chemical Test
pH Cl SO3 NO4 CO3
pH value Chlorine Content Sulphate Content Nitrate Content Carbonate Content
R E L A T I V E D E N SI T Y ( % )
P E R M E A B I L I T Y ( m / h o u r )
R E M A R K S
2.9
Tools and Plants for Soil Investigations. Back to contents page A.
Sampling, S.P.T.
i)
Tripod
ii)
Shell and Augar
iii)
Augar and wash boring
iv)
Pump
v)
Casing
vi)
Chaintong
vii)
Drill rod
viii)
Pipes
ix)
Monkey weight (For S.P.T.)
x)
Winch (Man/Mechanically operated)
xi)
Cathead
xii)
Sockets
xiii)
Samples a)
Open drive thin wall sampler
b)
Tube Sampler
c)
Split Spoon Sampler
d)
Piston sampler (Bishop Sampler)
xiv)
Polythin Packet
B.
Other Test Apparatus
i)
Vane Shear (4 blade vane)
ii)
Dynamic cone (50mm and 65 mm diameter with apex angle 60 Deg.)
iii)
Static cone (apex angle 60 Deg. & bore diameter 35.7 mm)
C.
Pressure Meter Test
i)
Menard Pressuremeter
D.
Rock Drilling
i)
Rotary drilling Machine with supporting equipments a)
Casing
b)
Drilled
c)
Core Barrel
d)
Drilling bid (T. C bit/Diamond bit)
E.
Resistivity Test
i)
Meggar Test
F.
Other Equipments
i)
Power Winch
ii)
Pulley
iii)
Chain
iv)
Buckets
v)
Tents, water drums, camping cots, tables, chairs & petrox.
G.
Transport Requirement
i)
Motor Cycle
ii)
Jeep
H.
Safety Equipments
i)
Safety Helmets
ii)
First Aix Box
iii)
Hand Gloves
iv)
Shoes
NOTE : a)
The quantities and capacities of the equipments will depend upon the nos. of bore hole, depth of the bore hole and completion schedule.
b) 3.0
Additional equipments may be required depending upon site conditions. Guidelines for Conducting Soil Investigation in Transmission Line Back to contents page Provision is made in Tower Package Specification for conducting soil investigation at various tower locations. However, it was observed in past that there were doubts about the selection of locations for conducting soil investigation. In view of the above to facilitate the procedure, the locations where the soil investigation is to be conducted are described below : The soil investigation is to be conducted at the following locations : 1.
Fissured rock is encountered with sub-soil water within 1.5 meter depth from ground level.
2.
Hard rock in combination with sub-soil water within 1.5 meter depth from ground level.
3.
Fissured rock in combination with water is encountered at the bottom of the pit with black cotton soil at top.
4.
Hard rock is encountered at the bottom with water and black cotton soil at top.
5.
Dry pure sand encountered in the pit.
6.
Predominantly silty sand mixed with clay or other soils (without subsoil water).
7.
Pure sand encountered with sub-soil water.
8.
Predominantly silty sand mixed with clay or othersoils encountered with sub-soil waters.
9.
Pure clay encountered with sub-soil water.
10.
If soil considered bad/trencherous.
11.
At the locations falling in back waters of a tank or reservoirs where there will be stagnation of water.
12.
River crossing locations.
13.
Tower used with 18M/25M extensions for power line crossings.
14.
Railway crossings. Soil investigation may be done at the locations mentioned above. It is not required to be done at the locations wherever soil could be easily classified and one of standard approved types of foundations could be adopted.
SECTION-II Tower Foundation
CHAPTER-1 General
___________________________________________________________________________ CHAPTER ONE ___________________________________________________________________________ GENERAL Back to contents page 1.0
Tower Foundations Back to contents page The tower foundations cost approx. 10 to 30 percent of overall cost of tower, or 5 to 15 percent of the cost of transmission lines, depending on the type of soil. Experience shows that while an inadequate foundation may lead to collapse of tower, an over design may prove very uneconomical. It is a good practice to check the tower for permissible deflection at the top. Since differential foundation settlement also causes tower deflection at the top, and if the total deflection at the top of the tower is to be restricted, the permissible deflection has to be carefully apportioned between the structure deflection and that caused by the differential foundation settlement. The design of a safe and economical foundation is based on soil properties, knowledge of soil structure interaction and settlement analysis of tower foundation.
1.1
Loads, Safety Factors and Settlement Back to contents page
1.1.1
Loads
The loads on foundation are determined from an analysis of the tower. The foundation is called upon to resist the following types of forces : (i)
Uplift
(ii)
Downwards
(iii)
Lateral load and
(iv)
Overturning moment
The basic vertical forces are derived from the deadweight of the tower and the conductors. The wind contributes to the horizontal force on the tower, producing not only shear force (lateral load) on the foundation, but also an uplift on the windward side of the structure and a downthrust on the other. The uplift or the compression forces are of primary concern in tower foundation design as shown in fig. l. In the case of the heavy angle and terminal structures, however, one pair of legs will be permanently subjected to compression and the other pair to uplift, due to the permanent heavy loads imposed by the deviation of the line. In this case, it is the general practice to design all the four footings to withstand both types of loading. 1.1.2
Safety Factors
The foundations are generally designed for factor of safety which are 10 percent in excess of those adopted for towers. Accordingly, the overload factors assumed in the design are 2.2 under normal conditions and 1.65 under broken-wire conditions. However, IS:802-1977 (Part III), relating to transmission line tower foundations, does not make any distinction with regard to factors of safety as between towers and foundations.
1.2
Classification of Soils Back to contents page The design of the tower foundation depends on the nature of loading and the type of soil that supports the foundation. The soils are broadly classified as: i)
Sandy soil (loose, medium and dense),
ii)
Clayey soil (soft, medium and stiff),
iii)
Clayey sand (sandy clays, silty clays, clayey and silty sand), mixed soil.
iv)
Rock (soft, medium and hard)
The following laboratory tests are usually conducted from the soil samples collected: i)
Visual examination and other identification tests.
ii)
Determination of in-situ density (r).
iii)
Determination of strength parameters, namely, cohesion C and angle of internal friction 0, settlement characteristic such as rate of settlement (D/t), compression index Cc etc. and
iv)
Determination of; elastic properties-Modulus of compressibility (k), coefficient of lateral subgrade reaction (C), etc.
Among the field tests, the Standard Penetration Test (SPT) is extensively adopted. In the Standard Penetration Test (SPT), a 64 Kg weight is dropped 76 cm to drive a sampling spoon into the ground. The no. of blows required to push the spoon to a given depth is corelated with a no. of soil properties. The advantage of SPT is that it is relatively quick, simple and inexpensive; but it is also subjected to many kind of errors. Also, correlations of SPT measurements with those of soil stress and other parameters are not particularly reliable.
In the Standard Core Penetration test, a shaft with a conical tip is slowly pushed into the ground while electrical transducers measure both tip pressure and side friction. The SCPT generally gives more accurate measurement than the SPT. It is also a faster method to identify problem soils. The SPT value N obtained from the field, is corrected for overburden pressure in accordance with the chart shown in Fig. 2. The SCPT gives the point resistance qc and side friction fc. The SPT value N and the SCPT value qc are related as shown in table (1) below. Table (1) - Correlation between SPT value N and SCPT value qc Soil Type
q/n
Clays
2.0
Silt, sandy silt and slightly cohesive silt and mixture
2.0
Clean fine to medium sands and slightly silty sands
3-4
Coarse
1.3
Sands and sands with little gravel
3-6
Sandy gravels and gravel
8-10
Properties of Soil Back to contents page The following soil properties are used in the design of different type of foundations: 1.
Density
2.
Relative density Dr
3.
Angle of internal friction for sandy soil
4.
Unconfined compressive strength Cu and cohesion C for clayey soil.
5.
Modules of compressibility Es
6.
Coefficient of lateral subgrade modules (C for sand and k for clay)
7.
Poisson's Ratio n
8.
Compressive strength of rocks s
9.
Ultimate bond strength of rock-anchor interface. Table below gives the above properties and classify the soils and rocks.
1.4
Data For Foundation Design Back to contents page The following data are usually required for a proper selection of type of foundation, its design and construction: 1.
Route map showing proposed layout of tower and topography.
2.
Selection of soil pits for soil data.
3.
Selection of sites for SPT.
4.
General layout of the tower and the loads at the foundation level.
5.
Meteorological data " wind, earthquake and frost penetration particulars.
6.
Max. allowable settlement at the base of the tower considering the permissible deflection at the top as H/140.
7.
In the case of river crossings:
a.
A site plan with details of crossing of at least 90m upstream and downstream from the central line
of the crossing.
b.
Outline of banks.
c.
Direction of flow of water.
d.
Alignment of crossing and location of towers.
e.
A cross section of the river at the proposed site of crossing, showing bed-line, banks, ordinary flood level, low water level, the highest flood, estimated depth of scour etc.
f.
The maximum and mean velocity of water current.
Notes: 1.
For non-cohesive soils the value of safe bearing capacity are to be reduced by 50 percent if the water table is above or near the base of footing.
2.
The values of safe bearing capacities do not take into effect the shape and size of footing, cohesion C, angle of internal friction 0, effect of eccentricity, the SPT value N, etc. considered as average and approximate.
Hence, the values are to be
3.
For other types of soil such as black cotton and peat, soil investigations have to be necessarily carried out for determining the safe bearing capacity. Table (2) Relation between N, c, Dr, for sandy soil
Description
SPT value (N)
Density () gm/cc
Relative density Dr
Very loose Loose Medium Dense Very Dense
0-4 4-10 10-30 30-50 >50
1.1 to 1.6 1.45 to 1.85 1.75 to 2.1 1.75 to 2.25 2.1 to 2.4
0-15 15-35 35-65 65-85 85-100
Angle of internal friction <28 28-30 30-36 36-41 >41
Table (3) Relation between N value, and unconfined compressive strength Cu and cohesion C for clays Consistency
SPT Value N
Soft Medium Stiff Very stiff Hard
0-4 4-8 8-15 15-30 >30
Unconfined compressive strength C kg/cm2 0-0.5 0.5-1.0 1.0-2.0 2.0-4.0 >4.0
Cohesion C kg/cm2
0-0.25 0.25-0.5 0.5-1.0 1.0-2.0 >2
Reduction factor for side friction a of bore pile 0.7 0.5 0.4 0.3 0.3
Table (4) Safe bearing capacity Type of rocks/soils Rocks Rocks hard without lamination such as granite Laminated rocks such as sand stone Rock desposits such as shale Soft rock Non-cohesive soils
Safe bearing capacity Kg/cm2 33 16.5 9.0 4.5
Gravel, sand and gravel, compact and offering high resistance to penetration when excavated by tools Coarse sand, compact and dry Medium sand, compact and dry Fine sand, silt (dry lumps easily pulverized by the fingers) Loose gravel or sand gravel mixture loose coarse to medium sand, dry Fine sand, loose and dry Cohesive soils Soft shale, hard or stiff clay in deep bed dry Medium clay, readily indented with a thumb nail Moist clay and sand clay mixture which can be indented with strong thumb pressure Soft clay indented with moderate thumb pressure Very soft clay which can be penetrated several inches with the thumb Black cotton soil or other shrinkable or expansive clay in dry condition (50 percent saturation)
4.5 4.5 2.5 1.5 2.5 1.0 4.5 2.5 1.5 1.0 0.5 1.5
Table (5) Modulus of compressibility E, and Poisson’s ratio for soils Soil type Clay Very soft Soft Medium Hard Silt Sand Silty Loose Dense Gravel Loose Dense
Modulus of compressibility E. kg/cm2
Ratio
3-30 20-40 45-90 70-200 20-200
0.1- 0.5
0.3-0.35
50-200 100-250 500-1,000
0.2-0.4
500-1400 800-2000
Reliable data Not available
CHAPTER-2 Types of Foundations
___________________________________________________________________________ CHAPTER TWO ___________________________________________________________________________ TYPES OF FOUNDATIONS Back to contents page 2.0
Introduction Back to contents page The foundation are classified as shallow or deep based on Df/B ratio Where Df = Depth of foundation and B = Breadth of foundation If Df / Bl, it is classified as a deep foundation. Piles are classified as deep foundation. Even though footing may have greater depth than the breadth in some circumstances, they are Created as shallow foundations for the analysis of bearing capacity. This approximation leads to a conservative estimate of the factor of safety and is, therefore, adopted for convenience and ease in calculations.
2.1
Types of Foundation Back to contents page This foundation work requiring excavation and backfill operation is quite satisfactory from design point of view. The knowledge of soil mechanics and the necessity of erecting towers on a variety of soils have made it possible and necessary for the designer to adopt new innovations and techniques. As a result several types of tower foundations have been derived and successfully used. Some of the more common types of foundation, mainly for broad based towers are briefly described below.
(a)
Concrete Pad and Chimney type (Fig.3) This is the most common type of footing used in India and some countries of the continent. It consists of a plain concrete footing pad, the size and depth of which are decided either on the basis of bearing area necessary for transmission of vertical downward load or from consideration of the amount of holding power required to resist the uplift force. The stub angle is taken inside and effectively anchored to the bottom pad by cleat angle and keying rods; and the muff or the chimney with stub angle inside works as a composite member. The pad may be either pyramidal (Fig.3a) or stepped (Fig.3b).
(b)
Steel Grillage (Fig.4) Steel grillage can be of various designs. Generally it consists of a layer of steel beam as pad for the tower leg by means of heavier joints or channels resting cross-ways on the bearing beams. Grillage footings require much more steel than a comparable concrete footing but erection cost is only a fraction of that of the concrete footing resulting in often economical and always quicker construction. Other advantages are that the complete foundation can be purchased from the manufacturer of towers alongwith the tower members.
The chief objection to earth grillage is that the steel may be easily attacked by corrosive constituents of the soil, and that the periodical excavation necessary for purposes of maintenance would loosen the soil and consequently lessen the anchorage until the earth consolidates again. (c)
Concrete spread footings
There are several types of concrete spread footings which can be designed for tower foundations. The two most common types of these are shown in (Fig. 5). In the slopping pedestal type the centroid of the base is in line with the batter of the tower legs and footing pedestals, reducing the additional overturning moment to that caused only by the horizontal component of the load in the lowest diagonal above the top of the pedestal. (d)
Augured Foundation (Fig.6)
The cast in situ reinforced concrete augured footing has been extensively used in U.S.A., Canada and many countries in the continent. The primary benefits derived from this type of foundations are the saving in time and manpower. Holes can be driven upto one meter diameter and six meter deep. The truck carrying the power augur is usually a cross country type of all wheel drive. Usually, stiff clays and dense sands are capable of being drilled and standing up sufficiently long for concreting works and installation of stub angle or anchor bolts, whereas loose granular material may give trouble during construction of these footings. Ben-tonite slurry or similar material is sometimes used to stablize the drilled hole.
(e)
Grouted rock footing (Fig. 7) Grouted rock footings or rock anchors are suitable in the areas with rock outcrops. The anchoring strength will depend on the bond between the grout and the surface of the anchor rods/bars. Anchor strength can be substantially increased by provision of mechanical anchorages, such as use of eye-bolt, fox-bolt or threaded rods as anchoring bars or use of keying rods in case of stub angle anchoring. The effective anchoring strength should preferably be determined by testing.
(f)
Precast Concrete Foundations (Fig.8) Due to difficulties inherent in getting good quality concrete in the isolated tower locations, attempts have been made to manufacture foundations either reinforced or prestressed in the'.factory. In Russia and some other Europian countries, precast reinforced spread footing of the type shown in (Fig. 8) is reported to have been successfully used. Primary advantages of the prefabricated foundations are: (i) better control over quality of concrete and workmanship (ii) saving in labour cost and (iii) repeated use of formworks and more economical use of materials of construction due to working under factory condition. Major handicaps in the use of prefabricated foundations are, however, the limitations of transport and handling facilities available for installations of the completed footings at the site.
(g)
Pile Foundations (Fig. 9) When the soil has a poor bearing capacity or the foundation is to be located on filled up soil, pile foundation may be adopted. The downward vertical load on the foundations is carried by the piles through skin friction or bypoint bearing while the uplift is resisted by the dead weight of the concrete in piles and pile caps with appropriate correction for floatation plus the pullout value of the piling. For carrying heavy lateral loads, batter piles may be advantageously used. Piles may be of different type such as driven-precast piles, bored piles with or without under reams.
(h)
Special Types of Footings (Fig. 10) There can be several other types of tower foundations made of mass concrete block foundation (Fig.10), tubular pile, pressed steel anchor, etc., apart from a variety of special footings. Each of these, under certain conditions, can do the job better than any other that could be conceived. The suitable type of foundations will, above all, be influenced by the forces to be accommodated, the sub soil condition, transportation and the available construction facilities.
(i)
Raised Foundation In case the foundation is surrounded by stagnant/flood water for a long time of the year, raised chimney foundations are to be adopted so that steel parts are not corroded. In this case chimneys are generally raised by about 500mm above the HFL.
(j)
Shallow Depth Foundation: Whenever the normal depth foundations cannot be constructed at site due to excessive seepage of heavy sub-soil water then reduced depth foundations are to be adopted. However, in all above cases engg. approval is prerequisite. In such locations soil investigation to be carried out to ascertain the properties of the soil for the design of the foundation.
CHAPTER-3 Classification and Stub Setting
___________________________________________________________________________ CHAPTER THREE ___________________________________________________________________________ CLASSIFICATION AND STUB SETTING Back to contents page 3.0
Line Construction Back to contents page Transmission line construction comprises the following phases:
3.1
(i)
Investigation and survey
(ii)
Transportation
(iii)
Foundations
(iv)
Tower assembly
(v)
Stringing
Investigation And Survey Back to contents page In the earlier section on line surveys, the various aspects relating to investigation and survey have been covered in detail.
3.2
Transportation Back to contents page The weight of materials and equipment required for building a transmission line tower may total several hundred tonnes, while construction sites are usually scattered over a wide area. Logistic operations thus become a major factor in these projects. Especially in mountainous terrain, road transportation facilities are poor and effective temporary construction routes are limited. All material transport shall be undertaken. in vehicles suitable for the purpose and
free from effect of any chemical substances. Tower members should be loaded and transported in such a manner that these are not bent in transit and sharp bend corners are not opened up or damaged. 3.3
Foundation Back to contents page The construction of tower foundations shall be in accordance with IS 4091:1979 and Power Grid specifications.
3.3.1
Check Survey This will be conducted to make a check on detailed survey and to locate the peg marks and the tower positions on ground conforming to the survey charts. In the process it is necessary to have the pit centres marked according to the excavation marking charts. The levels, up or down, of each pit centre with respect to the centre of the tower location shall be noted and recorded for determining the amount of benching or earthwork required to meet design requirements of the foundation. If the levels of the pit centres be in sharp contrast with the level of the tower centre (say beyond a slope of 1:4), suitable "leg extension" may be deployed as required.
3.4
Preparation of Foundation Site Back to contents page
3.4.1
After tower spotting is done during check survey, it is often the case that the area within the base of the tower is found uneven in level. Minor variation in level can be ignored but variations in level of more than 60 cms are to be dealt with benching the area to the reference level of centre peg. The foundation shall be placed at the design depth with reference to the centre peg level. The
area below the centre peg shall be back filled to get a leveled surface. If the level of back filling is considerably high, the filled area shall be enclosed by a revetment wall to prevent erosion. 3.4.2
In Hilly areas the difference of levels in the four legs is generally very high resulting in large quantity of benching and massive revetment walls, which will be very uneconomical. In these cases special hillside extensions are provided to place the four legs at different elevations.
3.5
Type of Foundation to be Adopted Back to contents page
3.5.1
The following standard types of foundation are approved in Powergrid for adoption in transmission lines for different towers:-
3.5.2
i)
Normal dry
ii)
Wet
iii)
Partially submerged
iv)
Fully submerged
v)
Dry fissured rock
vi)
Wet fissured rock
vii)
Hard rock foundation.
viii)
Black cotton soil foundation
The above foundations are designed for the corresponding predominantly prevalent soils in the pits. However, there will be cases where a combination of soils in the pits may be observed and correct classification of the standard foundations is required to be done.
3.5.3
Type of foundations to be adopted with reference to the soils and sub-soils waters encountered in the pits are indicated in Table-1 to 3. Foundations may
be classified and adopted accordingly. In certain classifications of soils with sub-soil waters (items 6(b) and 7(b) of Table-1, items 1(b) and 2(c) of table 2 and items 1,2 & 3 of Table 3) standard foundations cannot straight away be adopted. 3.5.4
If the soil conditions differ with the four legs of the same tower necessitating adopting of different types of approved foundation for the different legs of the tower, classification of foundations may be done for each of the pits as required by the actual soil conditions in the pits.
3.5.5
If site feels that soil encountered at any of the locations do not tally with the description of soils given in the Annexure enclosed or if the soils are considered very bad/tracherous, foundations may not be decided at such locations by the site. Classification of the foundations of such locations may be done in consultation with Corporate Engineering department. If the locations fall in the back water of any river, tank or reservoir, the depth of the back water at those locations and the duration of the stagnation of water at those locations is to be ascertained and foundation to be decided after studying the detailed soil report.
Table (1) Adoption of Foundations in Different Soils Sl. No. (1) 1. a) b)
Types of Soil Encountered (2) In good soil Where black cotton soil does not extent
Type of Foundation to be Adopted (3) Normal dry
beyond 30% of the depth from top with good c)
soils thereafter Silty sand mixed with clayey soil (In all the above cases water table is not encountered in
2.
a) b)
the pit) In paddy fields and sugar cane fields. Where black cotton soil exceeds 30 and extends up to 45% from the Ground level and
c)
good soil thereafter. Where sub-soil water is encountered in the
d)
pit beyond 1.5 m from ground level. Where silty sand mixed with clayey soil and
Wet
water encountered in the pit beyond 1.5 m 3.
a)
from ground level. Where black cotton soil extends upto 60% of
b)
the depth from G.L. and good soil thereafter. Where sub-soil water is encountered in the
Partially Submerged
pit between 0.75m depth and 1.5m depth c)
from ground partially level. Where silty sand mixed with clayey soil and water table in the pit is between 0.75m depth
4.
a)
and 1.5m depth from ground level. Where sub-soil water is encountered in the
b)
pit within 0.75m depth from ground level. Where silty sand mixed with clayey soil and water table in the pit is within 0.75 m from
5.
a)
G.L. Where normal soil encountered with fissured rock at the bottom without the presence of water.
Fully Submerged
6.
b)
Where fissured rock is predominant in the pit
c)
without the presence of water Where hard rock thickness at the bottom of
a)
the pit is less than 2.0m Where fissured rock is encountered with sub
Dry fissured rock
Wet fissured rock
soil waster after 1.50m depth from ground b)
level Where fissured rocks is encountered with
Soil investigation is to be properly
sub-soil water within 1.5m depth from
conducted at this location and the
ground
contractor has to develop new fdn. Design based on soil report and get
7.
a)
approved from Engg. Deptt. Hard rock
Wherever hard rock is encountered and the thickness of hard rock layer below the
b)
bottom of fdn. Is more than 2 meter Wherever hard rock is encountered with subsoil water
Soil investigation is to be conducted at this location & the contractor has to develop new fdn. Design based on soil report and get
8.
Wherever black cotton soil extends beyond 60% of
approved from Engg. Deptt. Black cotton soil fdn.
the depth from ground level.
Table (2) Black cotton soil in combination with rock Sl. No. Types of Soil Encountered (1) (2) 1. Black cotton soil with fissured rock
Type of Foundation to be Adopted (3)
combination a) If fissured rock is encountered at the Dry fissured rock foundation as per bottom of pit (with black cotton soil at top) for approved drg. may be adopted with a depth of not less than 1000mm or the wet chimneys because of black thickness of the bottom slab concrete of dry cotton soil encountered in the top fissured rock foundation whichever is less.
portion of the pit.
b)
If fissured rock in combination with Wet fissured rock foundation is to be
water is encountered at the bottom of the pit adopted. 2.
with black cotton soil at the top. Black Cotton Soil with hard
Rock
Combination a) If the hard rock is encountered at the Hard rock fdn. Design to be adopted bottom of the pit (with black cotton soil at top) with wet chimneys because of the and the thickness of the hard rock layer below black cotton soil encountered in the foundation is more than 2m. top portion of the pit. b) If hard rock encountered at the bottom Fissured rock foundation design to be of the pit with black cotton soil at the top and adopted with wet chimneys because hard rock layer depth is less than 2m. of the black cotton soil at the top. c) If hard rock is encountered at the Wet fissured rock foundation as per bottom with water and black cotton soil at top approved drgs. are to be adopted. and hard rock layer depth is less than 2m.
Table (3) Sand in Combination with Sub-soil water Sl. No. Types of Soil Encountered (1) (2) 1. Predominantly sand mixed with clay or other
Type of Foundation to be Adopted (3) Dry sandy soil foundation may be
2.
soil (without sub-soil water) Predominantly sand mixed with soils
adopted. FS/Wet sandy soil foundation may be
3.
encountered with sub soils water in the pits Pure sand encountered with sub-soil water
adopted depending on water table. Same as above
inside the pit
Table (4) Clay Mixed with Silty Sand Sl. No. Types of Soil Encountered (1) (2) 1. Pure clay encountered without water
Type of Foundation to be Adopted (3) Dry black cotton foundation may be adopted.
2.
Predominantly clay mixed with silty sand
Wet black cotton foundation may be
3.
encountered with sub-soil water in the pits. Predominantly silty sand mixed with clay
adopted. Normal fdn. Based on the water table
encountered with sub-soil water.
classification can be adopted.
Note : To facilitate foundation classification a check format has been developed and enclosed at Chapter-10 (Page Nos. 130, 131 & 132). 3.6
Pit Marking Back to contents page
3.6.1
The relevant drgs., Profile duly approved should be available at site with each working gang.
3.6.2
The following tools and plants (T&P) should be available with each working gang:i)
Ranging rods with flag
ii)
Dumpy level with stand.
iii)
Survey umbrella
iv)
One second theodolite and stadia method with calibrated levelling stares.
3.6.3
v)
Engineer's chain of 30 m length with 10m marking intervals.
vi)
Stones, Wooden Pegs, nails, spade, pick axe etc.
Reference Level The reference level is the level at the centre peg of the foundation location. The depth of all the four pits are to be measured from this reference point. The reduced level of the centre peg to be measured correctly and to be verified with the profile drg.
3.6.4
Pit marking shall be carried out according to the pit marking chart.
The design office will furnish the site with an excavation pit marking chart or excavation plan which gives the distance of pit centres, sides and corners with reference to centre point of tower. The distances are measured and each pit boundaries are marked in the field by means of spade or pick axe along the sides of the pit. 3.6.5
In case of open cut foundation the pit sizes shall be determined after allowing of 150 mm all round. No margin is necessary in case of undercut foundation. The depth of excavation at the pit centre shall be measured with respect to tower centre level.
3.6.6
While excavating care should be taken that earth is cut vertically/Tapered/In steps as per the site requirement to avoid any mishap during excavation. A typical excavation chart is enclosed. The proceeding and succeeding span on both sides of the centre of location shall be measured correctly and verified in order to ensure the exact location of the centre peg. For tangent towers pits are to be marked along the centre line through previous location and next location.
3.6.7
For angle towers pit marking is done along the bisection of angle of deviation. While carrying out this work the angle of deviation and type of tower is to be tallied with the profile. The bottom of the excavated pit shall match with originally marked pit plan.
3.6.8
The land mark and topography around the location should be carefully observed and tallied with the approved profile. The distinct feature shown in the profile drg. should normally match with prevailing site conditions.
3.6.9
On a slopy ground, care should be taken to take only horizontal distances from-centre to centre as per the pit marking charts. Excavation of the pits upto the desired level shall be done with respect to centre level of the pit.
3.6.10
The excavated earth shall be dumped on the outer edges of the pits away from the base of the tower to a minimum distance equal to the depth of the pit to avoid collapse of the free standing sides of the pit during excavation or concreting.
3.6.11
For the sake of reference the pits of the towers shall be designated as shown in the figure (Fig. 11).
3.7
Shoring and Shuttering Back to contents page
3.7.1
Shoring and shuttering shall be done keeping in view the requirements given in IS 3764:1966
3.7.2
In pits excavated in sandy soil or water bearing strata and particularly black cotton soil where there is every likelihood of pits collapsing, shoring and shuttering, made out of timber planks 30-35 mm thickness or steel frames
of
adequate strength to suit the requirement, will be provided. 3.7.3
Sand Bedding/stone bedding will be provided in foundations of marshy and wet Black Cotton foundations.
3.8
Dewatering Back to contents page
3.8.1
Dewatering shall be carried out manually or by mechanical means power driven pumps to facilitate excavation and casting of foundation. The pumps shall be suitable for handling mud water.
3.8.2
In areas where sub-soil water recoupment is heavy and where water cannot be controlled even by use of power driven pumps well point system is used for controlling water. In this system a grid of pipes are laid around the area where the pits are excavated and the system is very effective in pumping operation. The pit can be excavated avoiding risk of collapse of earth. This will ensure proper quality of concreting.
3.8.3
Another method is by drilling bore holes of a deeper pit much below foundation level for pumping out water by ordinary pumps. Number of boreholes depend on the volume of sub soil water.
3.8.4
In areas where sub-soil water recoupment is very rapid and water cannot be controlled, shallow foundations will be useful.
3.9
Excavation in Rock Back to contents page For excavation in hard rock, blasting can be resorted to. Reference shall be made to statutory rules for blasting and use of explosives for this purpose. No blasting is permitted near permanent work or dwellings. Blasting shall be so made that pits are excavated as near to the designed dimensions as practicable.
3.9.1
The work of blasting in rock is carried out in three separate operations. (a)
Drilling of holes to hold explosive charge.
(b)
Charging of the drilled holes
(c)
Fixing the charge
(a)
Drilling of Holes to hold explosive charge
i)
Drilling of holes to hold the explosive charge may be done either manually or with an air compressor as per the requirement at the site.
ii)
The equipment for hand drilling is simple but requires more man hours and generally consists of a set of Jumpers or Drills which are usually made from 22 mm diameter hexagonal steel bars.
iii)
The jumpers are 1m, 1.25m and 1.5m long and are suitably shaped. They must be tempered when sharpened. A 2 Kg. hammer is used for striking the jumper, which is given a slight rotation after each blow. The rate of progress by this in hard rock is 25 to 41 cm per hour.
iv)
When large quantity of rock is required to be excavated, an air compressor is used for drilling the holes.
(b)
Charging of the Drilled Holes
The charge consists of gelatine and detonator. Either half or a full gelatine is used as per the requirement. Detonator is normally pressed into the gelatine after making a hole in the gelatine with stick. Detonator is to be pressed into the gelatine till it is completely embedded in the gelatine. Then this assembly is placed into holes drilled. (c)
Fixing the Charge
The detonator leads are first interconnected to form a circuit and later the ends of this circuit are connected to the exploder with separate wires. The exploder is kept in a sheltered spot. To fire the shot the exploder handle is rotated at a high speed. 3.9.2
Procedure in case of Misfired Shots (i)
The misfired shot should not be touched.
(ii)
One should not approach a misfired shot until atleast 15 minutes have elapsed and all connections and' handle removed from the exploder.
(iii)
A second hole is to be drilled at a safe distance from the first in such a direction as well to keep the boring tool clear of the hole.
3.9.3
(iv)
Thus second hole is to be charged and fired.
(v)
The debris is to be searched thoroughly for unexploded detonator.
Additional Precautions To protect the persons and animals from injuries from flying debris depending on situation the numbers of holes to be drilled should be less deep and the pit should be covered with a steel plate. Such controlled blasting is an exception if the transmission line is kept away from villages and inhabited areas.
3.10
Procedure for setting Stubs at site by Combined Stub Setting Back to contents page
In the foundations of transmission line towers, a stub, generally of cross section of leg member of super-structure, is embedded in the foundation concrete at the same angle as that of superstructure main leg slope. To achieve this, there are three methods of setting the stubs in the pits for correct slope and alignment. i)
By using templates for individual stubs.
ii)
By using bottom section of tower as template.
iii)
By using a stub setting template common for all stubs.
i)
By using templates for individual stubs
For setting the stubs of towers' having hill side extensions or very broad base it becomes unwidely and uneconomical to use the combined template. The stubs are set separately using individual stub templates to maintain the slope. A steel channel or beam section of sufficient length to pass over the sides of the pits is used. A cleat .is welded to this to maintain the leg slope. After roughly aligning the individual templates with reference to centre peg, the stubs are fixed to the welded cleats. The stubs are aligned diagonally with the help of a theodolite stationed at from centre peg and adjusted by measuring diagonals. They are finally levelled precisely with the help of dumpy level. ii)
By using bottom section of tower as Template
If the bottom section of tower (for broad based towers of special extensions) is available before commencement of foundations, it can be used for setting the stubs. Two sides of the section are assembled on opposite faces along with stubs horizontally on the ground adjacent to the foundation pits. The sides are lifted and stubs are lowered into the pits and both sections are joined together with bracings. The assembly is aligned and the stubs are levelled by holding
the frame with cross bars under the bracing joints. Since alignment is difficult by dropping plumb, it is done with theodolite placed at centre peg. All bolts & nuts connecting the bottom section shall be fully tightened before concreting. iii)
By using a stub template common for all stubs
The Stubs are set with the help of the stub setting Templates which are supplied loose, ready to be assembled at site. All four excavated pits are to be lean concreted to correct level, sighted through and the stubs are to be placed on the lean concrete pad. Correct alignment is carried out by 0.90 kg plumb bob four in numbers hung from centre of horizontal bracings. Following is the procedure for Stub-setting at site: 1.
Assemble the Template as per the drawing sent alongwith the supply. A sample drg. of template is enclosed herewith for reference only.
2.
Set the Template 'as per the drawing at site.
3.
Place the stub-setting Jacks below the Template.
4.
Align Template, alongwith the line and centre it over the centre peg of the location.
5.
Fix up the stub to the Template and with the help of a dumpy level, level the Template corners to the required level.
6.
Ensure that all the four stubs are at the same level.
7.
Check the alignment and centring of the Template again.
8.
Check the diagonals distances of the stubs at least at two different levels.
9.
By placing on 8 to 12 screw jacks according to the length of Template, with a levelling instrument fine adjustment can be made by lifting/ lowering the screw jacks and the stubs can be perfectly levelled. This
ensures accurate verticality of the tower. For ensuring all towers in one line and cross-armd at right angle to it, four plumb bobs should dropped from the center of the horizontal members of the Template to correspond to the cross pegs and alignment pegs given during the line alignment survey for the tower location.
CHAPTER-4 Foundation Construction
___________________________________________________________________________ CHAPTER FOUR ___________________________________________________________________________ FOUNDATION CONSTRUCTION Back to contents page 4.0
Concrete Type Back to contents page For reasons of economy and progress it is normal practice to use coarse and fine aggregates available along with line route and/or nearest locations of the route. As such, it is not practicable to design the concrete mix and use controlled concrete. Moreover, since the quantity of concrete involved is rather small, ordinary plain or reinforced cement concrete given in IS 456:1978 shall be used in overhead line foundations.
4.1
Mixes Back to contents page For main foundation, M 150 or 1:2:4 (Volume) mix cement concrete generally used. For lean concrete sub-bases or pads, M 100 or 1:3:6 mix cement concrete may be used. The properties of concrete and mix proportions shall be 'in conformation to IS 456:1978. It shall be permissible to proportionate the concrete as follows: a)
Prepare a wooden measuring box of 35 liters capacity (that is. equal to 1 bag or 50 kg of cement with inside dimensions of not exceeding 30 x 30 x 30 cm or alternatively 34 cm diameter and 39 cm height.
The mix quantities according to the measuring box shall be as follows: S. No. Item
M 150
M 100
1.
Cement
1 bag
1 bag
2.
Sand
2 boxes
3 boxes
3.
Stone
4 boxes
6 boxes
4.
Water
1 box less
1 boxes less
3 liters
1 liters
b)
Measurement of water may be made with separate water-tight drums of the above size or with 1-or 2-litre mugs.
Note: For concreting the bored foundations by displac-ing the drilling muds, 10 percent extra cement in the mix is required. One bag of cement is taken to contain 50 kg or 35 liters of ordinary portland cement. 4.2
Sizes of Aggregates Back to contents page The coarse aggregates (stone) to be used shall be single size aggregates of 40 mm nominal size for slab/pyamid concrete and 20 mm nominal size for chimney concrete conforming to IS 383 : 1970. These sizes are applicable to ordinary plain cement concrete for RCC, the aggregates shall preferably be of 20 mm nominal size. The fine aggregate (sand) shall be of Zone I Grade conforming to IS:383 : 1970 which is the coarse variety with maximum particle size of 4.75 mm. Zone II Grade of fine aggregates may also be used.
4.3
Gravel Sub-base Back to contents page In case the foundation happens to be over fine sand, 80 mm chick gravel subbase may be provided, if considered necessary, under the' foundation. The maximum size of gravel or stone to be used shall be 80 mm.
4.4
Reinforcement Back to contents page All reinforcement shall be properly placed according to design drawing with a minimum concrete cover of 50 mm. The bars shall, however, be placed clear of stubs and cleats where interfering. For binding iron wire of not less than 0.9 mm shall be employed and the bars may be bound at alternate crossing points. The work shall conform to IS 2502 : 1963 wherever applicable. For bored footings, stub angle shall be used as reinforcement.
In case the foundation having steel reinforcement in pyramid on base slab, at least 50 mm Chick pad of lean concrete of 1: 3:6 nominal mix shall be provided to avoid the possibility of reinforcement rod being exposed due to unevenness of the bottom of the excavated pit. 4.5
Form Work Back to contents page
4.5.1
General The form work shall conform to the shape, lines and dimensions as shown on the design drawings, and be so constructed as to be regid during the placing & the compacting of concrete, and shall be sufficiently tight to prevent loss of liquid from concrete. It shall be of light design & easily removable without distortions and shall be of steel, hardwood or framed plywood. The inner surface coming in contact with concrete shall be smooth and free form projections. Window on one face shall be provided for pyramid forms to facilitate concreting in the lower parts which shall be fixed after concrete in the bottom part is placed. In bored footings form work may be needed only towards the top for the portion above ground level. The form work for slabs and pyramids shall be made symmetrical about the base of the chimney to ensure interchangeable faces as illustrated in Fig. 12.
4.5.2
Clearing and Treatment of Forms All rubbish, particularly chippings, shavings and sawdust and traces of concrete, if any, shall be removed form the interior of the forms before the concrete is placed. The surface in contact with the concrete shall be wetted and sprayed with fine sand, or treated with an approved composition before use,
every time. Concreting to be done for cold weather shall be as per IS 7861(Part 2) : 1981 4.5.3
Stripping Time under fair weather conditions (generally where average daily temperature is 20"C or above) , and where ordinary cement is used, forms may be removed after 24 to 48 hours of the placing of concrete. In dull weather such as in rainy periods or in very cold temperature, the forms shall be removed after 48 hours of the placing of concrete.
4.6
'Mixing, Placing and Compacting of Concrete Back to contents page
4.6.1
Mixing Concrete shall preferably be mixed in a mechanical mixer, but hand mixing shall be permissible. In case of emergency (when mechanical mixers are in use) such as failure of the mixers, or where it is not practicable to haul the mixers up to the location, and also for lean concrete sub-base, hand mixing may be resorted to. When hand mixing is adopted, it shall be carried out on water-tight platforms, such as 1.8 mm galvanized iron plain sheets properly overlapped and placed upon level ground. The coarse aggregates shall first be evenly spread out in required quantity over the sheets. The fine aggregates shall be evenly spread out over coarse aggregates. The aggregates shall then be thoroughly mixed together and levelled. The required amount of cement shall be spread evenly over the mixed aggregates and wet mixing shall start from one end with required amount of water suing showels. The whole lot shall not be wetted, instead mixing shall proceed progressively. If the aggregates are wet or washed, cement shall not be spread out, but shall be put in progressively.
For mixing in the mechanical mixers, the same order of placing ingredients in the drum shall be adopted, that is, coarse aggregates shall be put in first followed by sand, cement and water. Mixing shall be continued until there is a uniform distribution of material and the mass is unform in colour and consistency but in no case shall mixing be done for less than 2 minutes. If the aggregates are wet, the amount of water shall be reduced suitably. 4.6.2
Transporting Normally mixing shall be done right at the foundation. In places where it is not possible, concrete may be mixed at the nearest convenient place. The concrete shall be handled from the place of mixing to the place of final desposit as rapidly as practicable by methods which shall prevent the segregation or loss of any of the ingredients.
If segregation does occur during transport the
concrete shall be remixed before being placed. During hot or cold weather, concrete shall be transported in deep containers; the deep containers, on account of their lower ratio of surface area to mass, reduce the rate of loss of water by evaporation during hot weather and loss o'f heat during cold weather. 4.6.3
Placing and Compacting The concrete shall be placed and compacted before settling commences and should not be subsequently disturbed. The placing should be such that no segregation takes place. Concrete shall be thoroughly compacted during the placing operation, and thoroughly worked around reinforcement, around embedded fixtures and into corners of form work by means of 16 mm diameter poking bars pointed at the
ends. The poking bars be worked 100 times in an area of 200 mm square for 300 mm depth. Over compaction causes the liquid to flow out upward causing segregation and should be avoided. If, after the form work has been struck, the concrete surface is found to have defects, all the damaged surfaces shall be repaired with mortar application composed of cement and sand in the same proportion as the cement and sand in the concrete mix.
Such repairs shall be carried out well before the
foundation pits are back filled. Precautions to be taken on concrete work in extreme weather and under water, as per the provisions of IS 4565:1978. Field tests on workability of concrete and consistency may be carried out in the form of slump test in accordance with IS 1199:1959. 4.7
Back Filling Back to contents page Following opening of form work and removal of shoring and strutting, if any, back filling shall be started after repair, if any, to the foundation concrete. Back filling shall normally be done -with the excavated soil, unless it consists of large boulders / stones, in which case the boulders shall be broken to a maximum size of 80 mm. The back filling materials should be clean and free from organic or other foreign materials. The earth shall be deposited in maximum 200 mm layers, levelled and wetted and tamped properly before another layer is deposited. Care shall be taken that the back filling is started from the foundation ends of the pits, towards the outer ends. After pits have been back filled to full depth, the stub template may be removed.
The back filling and grading shall be carried to an elevation of about 75 mm above the finished ground level to drain out water. After back filling 50mm high earthen embankment (bandh) will be made along the sides of excavated pits and sufficient water will be poured in the back filled earth for at least 24 hours. 4.8
Curing Back to contents page The concrete after setting for 24 hours old shall be cured by keeping the concrete wet continuously for a period of 10 days after laying. The pit may be back filled with selected earth sprinkled with necessary amount of water and well consolidated in layers not exceeding 200 mm of consolidated thickness after a minimum period of 24 hours and thereafter both the back filled earth and exposed chimney top shall be kept wet for the remainder of the prescribed time of 10 days. The uncovered concrete chimney above the back filled earth shall be kept wet by providing empty cement bags dipped in water fully wrapped around concrete chimney for curing and ensuring that the bags are kept wet by the frequent pouring of water on them.
CHAPTER-5 Protection of Foundation
___________________________________________________________________________ CHAPTER FIVE ___________________________________________________________________________ PROTECTION OF FOUNDATIONS Back to contents page 5.0
Concrete Type Back to contents page
5.1
Uplift Resistance Back to contents page The transmission line foundations are designed to withstand both down thrust and uplift forces. The resistance of the soil in compression in reasonably well. However, the resistance to uplift is uncertain and there are many theories reported for uplift resistance in literature. These theories are generally based on a slip surface rising vertically from the edge of the footing or a surface rising at an angle of friction from the vertical, thus forming a frustum (Fig.13). Under the vertical surface theory the shear resistance along the sides of the plane or cylinder is calculated and added to the dead weight of the soil and footing. Under the angle of friction theory, the dead weight within the frustum is considered to provide resistance against uplift. Test results have shown that neither of these methods provide reliable results. The cone method is usually conservative at a shallow depth. This problem is solved by constructing revetment or benching around the complete tower foundation or individual tower leg.
The foundations are also required to be protected from landslide, earth slip., erosions of the hills due to flood etc. The Revetment or Benching also protects the foundation from the above. 5.2
Revetment Back to contents page Revetment is generally constructed at those locations where the angle of repose intersects the ground at a difference of about 1.0m below the centre peg level. Generally a wall is constructed around the individual tower leg or around the complete foundation enclosing all the four tower legs. Revetment is made around the complete foundation in case the tower base dimensions are smaller i.e. within 10.0m. However, in case the tower base dimensions are very very large, construction of Revetment around the individual Cower leg may be economical. The site engineer is required to make a cost comparison considering the revetment around the individual leg or all the four legs.
The Revetment wall can be constructed by random rubble masonry wall with rectangular cross section having a width of 450mm and a staggered depth of 1 1/2 times the exposed portion of wall above ground level. A Random Rubble masonry, wall of Trapezoidal cross section (Fig. 14) may be constructed for the difference of elevation above 1m. In case tower is located in hill slope i.e. where the difference in elevations is very large. Revetments may not be economical. In such cases leg extensions of structural steel can be designed for the standard length. No Revetment is to made for the purpose of stub setting. Revetments should not be done for levelling the-area under the tower base for the purpose of stub setting. The payment for the levelling the area and Trench excavations along the sides as well as diagonals of the tower legs is included in the unit rate of stub setting. 5.3
Benching Back to contents page When the line passes -through .the hilly/undulated terrain, levelling of the ground may be required for casting of the tower foundation as to protect the stub from corrosion. All such activities shall be termed as benching and shall include the cutting of excess earth above the centre peg level and filling the same in the area below the centre peg level. It is preferable to do the benching work after construction of the Revetment wall since the excavation will infringe with the filled soil of the benching work and cause inconvenience for excavation.
5.4
Protection of Foundation against Chemical Water Back to contents page
Whenever the chemicals are present in water in contact with steel or R.C.C. member it will have a deteriorating effect on concrete as well as steel. To prevent this, concrete incashing on the steel members to be done and Bituminious paint to be provided over the concrete surface. The concrete incasing to be done upto 200mm above the chemical water level. The bracing members are to be enclosed accordingly. Minimum 50 mm clear cover to be provided over the steel member. 5.5
Measurement of Volume for rivetment and benching Back to contents page
5.5.1
General There are three methods generally adopted for measuring the volume. They are : (i)
From cross-sections
(ii)
From spot levels
(iii)
From contours
The first two methods are commonly used for the calculation of each work while the third method is generally adopted for the calculation of of depressed area.
5.5.2
Measurement from Cross-Sections This is the most widely used method. The total volume is divided into a series of solids by the planes of cross-sections. The fundamental solids on which measurement is based are the prism, wedge and prismoid. The spacing of the sections depends upon the character of the ground and the accuracy required in the measurement. The area of the cross-section taken along the line are first calculated by standard formulae developed below, and the volumes of the prismoids between successive cross-sections are then calculated by either trapezoidal formula or by prismodial formula. The various cross-sections may be classified as (i)
Level section, (Figs. 15 and 16)
(ii)
Two-level section, (Fig. 17)
(iii)
Side hill two-level section, (Fig. 18)
(iv)
Three-level section (Fig. 19) and
(v)
Multi-level section (Fig. 20).
General notations : Let b = the constant formation (or sub-grade) width h = the depth of cutting on centre line w1 and w2 = the side widths, or half breadths, i.e., the horizontal distances from the centre to the intersection of the side slopes with original ground level.
h1 and h2 = the side heights, i.e., the vertical distances from formation level to the intersections of the slope with the original surface. n horizontal to 1 vertical = inclination of the side slopes. m horizontal to 1 vertical = the transverse slope of the original ground. A = the area of the cross-section. (a)
Level Section (Fig. 16)
In this case the ground is level transversely. h1 = h2 = h w1 = w2 = w = b/2 + nh
A = {b/2 + (b/2+nh)} h = (b+n) h (b)
Two-Level Section (Fig. 17)
Let O be the point on the centre line at which the two sides slopes intersect. Hence BH : HO : : N : 1 OR ho = b/2n The Area DCEBA = DCO + ECO- ABO = ½ { (h+b/2n) w1 + (h+b/2n) w2 – b2/2n) = ½ {w2+w2) (h+b/2n)-b2/2n) ……………………………………… (5.2) The above formula has been derived in terms of w1 and w2 and does not contain the term m. The formula is, therefore, equally applicable even if DC and CE have different slopes, provided w1 and w2 are known. The formula can also be expressed in terms of h1 and h2. Thus Area DCEBA = DAH+ EBH+DCH+ECH = ½ { (b/2) h2 + (b/2) h1 + hw2+hw1)} = ½ {b/2 (h1+h2) + h (w1+w2)………………………………………… (5.3)
The above expression is independent of m and n. Let us now find the expression for w1, w2, h1 and h2 in terms of b, h, m and n. BJ = nh1 ……………………………………………………………… (1) Also BJ = HJ-HB=w1 – b/2 …………………………………………. (2) Nh1 = w1 – b/2 ……………………………………………………….. (i) Also, w1 = (h1 – h) m Substituting the value of w1 in (i), we get Nh1 = (h1-h) m – b/2 Or h1 (m-n) = mh+b/2 Or h1 = (m/m-n) (h+b/2m)
Substituting the value of h1 in (i), wet get W1 = b/2+nh1=b/2+mn/m-n (h+b/2m) ………………………………….. (5.4) Proceeding in similar manner, it can be shown that h2 = (m/m+n) (h-b/2m) …………………………………………….……. (5.5) and w2 = b/2+mn/m+n) (h-b/2m) ……………………………………… (5.6) Substituting the values of w1 and w2 in equation (5.2) and simplifying, we get Area = (m2n/m2-n2) (h+b/2n)2-b2/4n ………………………………… (5.7) Similarly, substituting the values of w1, w2, h1 and h2 in the equation (5.3), we get Area = {n (b/2)2 + m2 (bh+nh2)}/(m2-n2) ……………………………… (5.8) (c)
Side Hill Two-Level Section (Fig. 18)
In this case, the ground slope crosses the formation level so that one portion of the area is in cutting and the other in filling. Now BJ = nh1
Also, BJ = HJ – HB = w1-b/2 & nh1=w1-b/2 …………………………………………………………..... (i) But w1 = (h1-h) m ……………………………………………………….. (ii)
Solving (i) and (ii) as before, we get h1 = (mn/m-n) (b/2m+h) ………………………………………………. (5.9) and w1 = b/2 + (mn/m-n) (b/2m+h) ……………………………..……. (5.10)
Let us now derive expression for w2 and h2 : IA = nh2 Also IA = IH – AH=w2-b/2 nh2 = w2-b/2 …………………………………………………………… (iii) Also w2 = (h+h2) m nh2 = (h+h2) m – b/2 …………………………………………………. (iv) and h2 (m-n) = b/2 – mh or h1 = (mn/m-n) (b/2m-h) …………………………………………… (5.11) Hence w2 = b/2+nh2=b/2+(mn/m-n) {(b/2m)-h} …………………… (5.12)
By inspection, it is clear that the expressions for w1 and w2 are similar; also expression of h1 and h2 are similar, except for –h in place of +h. Now area of filling = PBE=A1 (say), And, area of cutting = PAD = A2 (say), A1 = ½ (PB) (EJ) = ½ (b/2+mh) {(m/m-n) (b/2m+h)} = (b/2+mh)2/2 (m-n) ………………………………………………….. (5.13) and A2 = ½ (AP) (ID) = ½ {(b/2) – mh} [m/(m-n) {(b/2m) – h}] = { (b/2) – mh}2 /2 (m-n) …………………………………………… (5.14) (d)
Three –Level Section (Fig. 19)
Let 1 in m1 be the transverse slope of the ground to one side and 1 in m2 be the slope to the other side of the centre line of the cross section (Fig. 19). The expressions for w1, w2, h1 and h2 can be derived in the similar way as for case (b) Thus, w1 = (m1n/m1-n) (h+b/2n) …………………………………….. (5.15) w2 = (m2n/m2-n) (h+b/2n) ………………………………………….. (5.16) h1 = (h+w1/m1) = (m1/m1-n) (h+b/2m1) ………………………….. (5.17) h2 = (h-w2/m2) = (m2/m2+n) (h-b/2m2) …………………………… (5.18) The area ABECD = AHD+BHE+CDH+CEH = ½ [ (h2xb/2) + (h1xb/2) + hw2 + hw1]
= [b/4 (h1+h2) + h/2 (w1+w2)] ……………………………………… (5.19) (e)
Multi-Level Section (Fig. 20)
In the multi-level sections the co-ordinate system provides the most general method of calculating the area. The cross-section does provide with x and y co-ordinates for each vertex of the section, the origin being at the central point (H). The x co-ordinates are measured positive to the right and negatives to the left of H. Similarly, the y co-ordinates (i.e. the heights) are measured positive for cuts and negative for fills. In usual form, the notes are recorded as below : (h2/w2) (h1/w1) (h/o) (H1/W1) (H2/W2) If the co-ordinates are given proper sign and if the co-ordinates of formation points A and B are also included (one at extreme left and other at extreme right) they appear as follows : O/(-b/2) h/(-w2) h1/(-w1) h/o) H1/)+w1) H2/(+w2) o/+ (b/2) There are several methods to calculate the area. In one of the methods, the opposite algebric sign is placed on the opposite side of each lower term. The co-ordinates then appear as : O/(-b/2+) h2/ (-w2+) h1/(-w1+) h/(o) H1 / (+W1-) H2/(+W2-) o/(+b/2-) The area can now be computed by multiplying each upper term by the algebraic sum of the two adjacent lower terms, using the signs facing the upper
term. The algebraic sum of these products will be double the area of the crosssection. Thus, we get H = ½ [h2 ( +b/2-w1) + h1 (+w2+o) + h (+w1+W1) + H1 (o+W2)+H2 (-W1+b/2)] ………………………………………… (5.20) 5.5.3
The Prismoidal Formula The volumes of the prismoids between successive cross-section are obtained either by trapezoidal formula or by prismoidal formula. We shall first derive an expression for prismodal formula. A prismoid is defined as a solid whose end faces lie in parallel planes an consist of any two polygons, not necessarily of the same number of sides, the longitudinal faces being surfaces extended between the end planes. The longitudinal faces take the form of triangles, parallelograms, or trapezium. Let d = length of the prismoid measured perpendicular to the two end parallel planes. A1= area of cross-section of one end plane. A2 = area of cross-section of the other end plane. M = the mid-area = the area of the plane midway between the end planes and parallel to them. In fig. 21, let A1B1C1D1 be one end plane and A2B2C2D2 be another end plane parallel to the previous one. Let PQRST represent a plane midway between the end faces and parallel to them. Let Am be the area of mid-section. Select any point O in the plane of mid-section and joint it to the vertices of both the end planes. The prismoid is thus divided into a number of pyramids,
having the apex at A and bases on end and side faces. The total volume of the prismoid will therefore be equal to the sum of the volume of the pyramids. Volume of pyramid OA1B1C1D1 = 1/3 (d/2) A1 = (1/6) (A1d) Volume of pyramid OA2B2C2D2 = (1/6) (A2d) To find the volumes of pyramids on side faces, consider any pyramid such as OA1B1B2A2.
Its volume = 1/3 (A1B1A2B2) x h, where h = perpendicular distance of PT from O = 1/3 (d x PT) h = (1/3) d (2 OPT) = (2/3) d (OPT) Similarly, volume of another pyramid OC1D1D2 on the side face = (2/3) d (OSR) = (2/3) d (OSR) Total volume of lateral (side) pyramids = (2/3) d (PQRST) = (2/3) Am Hence, total volume of the pyramid = (1/6)A1d+(1/6)A2d + (2/3) d. Am
V = d/6 (A1+A2+4Am) …………………………………………..……. (5.21) Let us now calculate the volume of earth work between a number of sections having area A1, A2, A3 ………, An spaced at constant distance d apart. Considering the prismoid between first three sections, its volume will be, from equation (5.21). = (2d/6) (A1+4A2+A3), 2d being the length of the prismoid. Similarly, volume of the second prismoid of length 2d will be = (2d/6) (A2+4A4+A5), and volume of last prismoid of length 2d will be = 2d/6 (An-2+4An-1+An) Summing up, we get the total volume, V= (d/3) [A1+4A2+2A3+4A4+ … + 2An-2+4An-1+An] …………… (5.22) or V = (d/3) [(A1+An) + 4 (A2+A4+An-1)+2 (A3+A5+An-2)] This is also known as Simpson’s rule for volumes. Here also, it is necessary to have an odd number of cross-sections. If there are even number of sections, the end strip must be treated separately, and the volume between the remaining sections may be calculated by prismodial formula. 5.5.4
The Trapezoidal Formula (Average end area method) This method is based on the assumption that the mid area is the mean of the end areas. In that case, the volume of the prismoid of Fig. 21 is given by V = (d/2) (A1+A2) This is true only if the prismoid is composed of prisms and wedges only and not of pyramids. The mid area of pyramid is half the average area of the ends; hence the volume of the prismoid (having pyramids also) is over estimated. However, the method of end area may not be accepted with sufficient accuracy
since the actual earth solid may not be exactly a prismoid. In some cases, the volume is calculated and then a correction is applied, the correction being equal to the difference between the volume as calculated and that which could be obtained by the use of the prismoid formula. The correction is known as the prismoidal correction. Let us now calculate the volume of earth work between a number of sections having areas A1, A2, ……… An spaced at a constant distance d. Volume between first two sections = (d/2) (A1+A2) Volume between next two sections = (d/2) (A3+A4) Volume between last two sections = (d/2) (An-1+An) Total Volume = V=d {(A1+A2)/2+A2+A3+An-1} …………………… (5.23) 5.5.5
The Prismoidal Correction (Cp) As stated earlier, the prismoidal correction is equal to the difference between the volumes as calculated by the end-area formula and the prismoidal formula. The correction is always substractive, i.e. it should be substracted from the volume calculated by the end area formula. Let us calculate the prismoidal correction for the case when the end sections are level sections. Let A, w1, w2, h1, h2 etc., refer to the cross-sections at one end and A, w1, w2, h1, h2, etc., to the cross section at the other end. Now A=h (b+nh) And A = h (b+nh) Volume by end area rule is given by V = (d/2) [h (b+nh) + h (b+nh)] = d [bh/2+bh/2+nh2/2+nh2/2] ……………………………………………. (i) Again, the mid-area centre height = (h+h’)/2
Mid-area = {(h+h’)/2} [{b+n(h+h’)/2}] Volume by prismoidal formula given by V = d/6 [h(b+nh)+h’ (b+nh’)+4 {(h+h’)/2} x {(b+n(h+h’)/2}] V=d/6 [3bh+3bh’+2+nh2+2nh’2+2nhh’] =[bh/2+bh’/2+bh’/2+nh2/3+nh’2/3+nhh’/3] …………………………… (ii) Substracting (ii) from (i), we get the prismoidal correction, Cp = (dn/6) (h-h’)2 ………………………………………………… (5.24) Similarly, the prismoidal correction for other sections can also be drived. The standard expression for C2 are given below.
For two level section : C2 = d/6n (w1-w’1) (w2-w’2) …………………………………….. (5.25) For side hill two-level section ; Cp (cutting) = (d/12n) (w1-w’1) {(b/2+mh)-(b/2+m’h’)} ……….. (5.26) Cp (filling) = (d/12n) (w2-w’2) {(d/2-mh) – (d/2-m’h’) …………. (5.27) For three-level section : Cp = (d/12) (h-h’) {(w1+w2) – (w1’+w2’) …………………….. (5.28) 5.5.6
The Curvature Correction The prismoidal and the trapezoidal formulae were derived on the assumption that the end sections are in parallel planes. When the centre line of cutting or an embankment is curved in plane, it is common practice to calculate the volume as if the end sections were in parallel planes, and then apply the correction for curvature. The standard expression for various sections are given below. In some cases, the correction for curvature is applied to the areas
of cross-sections thus getting equivalent areas and then to use the prismoidal formula. (i)
Level section : No correction is necessary since the area is symmetrical about the centre line.
(ii)
Two-level section and three-level section ; Cc = (d/6R) (w12-W22) (h+b/2n) ………………………..…… (5.29) Where R is the radius of the curve.
(iii)
For a two-level section, the curvature correction to the area Ae/A per unit length ………………………………………… (5.30)
Where e= the eccentricity, i.e., horizontal distance from the centre line to the centroid of the area = w1w2 (w1+w2)/3An …………………………. (5.31) The correction is positive if the centroid and the centre of the curvature are to the opposite side of the centre line while it is negative if the centroid and the centre of the curvature are to the same side of the centre line. (iv)
For side hill two-level section : Correction to area = Ae/R per unit length ……………………. (5.32) Where e = (1/3) (w1+b/2-nh) for the larger area …………….. (5.33) And e = (1/3) (w2+b/2nh) for the smaller area ……………… (5.34)
5.5.7
Volume from Spot Levels In this method, the field work consists in dividing the area into a number of squares, rectangles or triangles and measuring the levels of their corners before and after the construction. Thus, the depth of excavation or height of filling at every corner is known. Let us assume that the four corners of any one square of rectangle are at different elevations but lie in the same inclined plane. Assume that it is desired to grade down to a level surface a certain distance
below the lowest corner. The earth to be moved will be a right truncated prism, with vertical edges at a, b, c and d [Fig. 22]. If ha, hb, hc and hd represent the depth of excavation of the four corners, the volume of the right truncated prism will be given by V = {(ha+hb+hc+hd)/4} x A ………………………………………. (5.35) = average height x the horizontal area of the rectangle. Similarly, let us consider the triangle abc of Fig. 22. If ha, hb and hc are the depths of excavation of the three corners, the volume of the truncated triangular prism is given by V = {(ha+hb+hc) / 3} x A …………………………………………. (5.36) = (average depth) x horizontal area of the triangle.
Volume of a group of rectangles or squares having the same area.
Let us now consider a group of rectangles of the same area arranged as shown in Fig. 22. It will be seen by inspection that some of the heights are used once only, some heights are common to two rectangles (such as at b), some heights are common to three rectangles (such as at e), and some heights are common to four rectangles (such as at f). Thus, in Fig. 22, each corner height will be used as many times as there are rectangles joining at the corner (indicated on the figure by numbers). Let h1 = the sum of the heights used once. h2 = the sum of the heights used twince. h3 = the sum of the heights used thrice. h4 = the sum of the heights used four times. A = horizontal area of the cross-section of one prism. Then, the total volume is given by V = A (1h1+2h2+3h3+4h4)/4 …………………………………… (5.37) Volume of a group of triangles having equal area [Fig. 22] If the ground is very much undulating, the area may be divided into a number of triangles having equal area. In this case, some corner heights will be used once [such as point a of Fig. 22], some twice (such as at d), six times (such as at f), and seven times (such as at j). The maximum number of times a corner height will be used as many times as there are triangles joining at the corner (indicated in the figure by numbers). Let h1 = the sum of the heights used once. h2 = the sum of the heights used twice. h3 = the sum of the heights used thrice. …………………………………………
………………………………………… h8 = the sum of height used eight times. A = area of each triangle. The total volume of the group is given by V = A/3 (1h1+2h2+3h3+4h4+5h5+6h6+7h7+8h8) ……….. (5.38) 5.5.8
Volume from Contour Plan The amount of earth work or volume can be calculated by the contour plan area. There are four distinct methods, depending upon the type of the work. a)
By Cross-Sections It was indicated, that with the help of the contour plan, cross-section of the existing ground surface can be drawn. On the same cross-section, the grade line of the proposed work can be drawn and the area of the section can be estimated either by oridinary methods or with the hel of a planimeter.
Thus, in Fig. 23, the irregular line represents the origin ground while the straight line ab is obtained after grading. The area of cut and of fill
can be found from the cross-section. The volumes of earth work between adjacent cross-sections may be calculated by the use of average and areas. (b)
By Equal Depth Contours In this method, the contours of the finished or graded surface are drawn on the contour map, at the same interval as that of the contours. At every point, where the contours of the finished surface intersect a contour of the existing surface the cut or fill can be found by simply subtracting the difference in elevation between the two contours. By joining the points of equal cut or fill, a set of lines is obtained (represented by thick lines in Fig. 24). These lines are the horizontal projections of lines cut from the existing surface by planes parallel to the finished surface. The irregular area bounded by each of these lines can be determined by the use of the planimeter. The volume between any two successive area is determined by multiplying the average of the two areas by the depth between them, or by prismoidal formula. The sum of the volume of all the layers is the total volume required.
Thus, in Fig. 24, the ground contours (shown by this continuous lines) are at the interval of 1.0 meter. On this a series of straight, parallel and equidistant lines (shown by broken lines) representing a finished plane surface are drawn at the interval of 1.0 meter. At each point in which these two sets of lines meet, the amount of cutting is written. The thick continuous lines are then drawn through the points of equal cut thus getting the lines of 1, 2, 3 and 4 metres cutting. The same procedure may be adopted if the contours of the proposed finished surface are curved in plan. Let A1, A2, A3 …………. Etc. be the areas enclosed in each of the thick lines (known as the equal depth contours). This will be the whole area lying within an equal depth contour line and not that of the strip between the adjacent contour lines. h = contour interval V = Total volume Then V = h/2 (A1/A2) by trapezoidal formula
Or h/3 (A1/4A2/A3) by prismoidal formula. (c)
By Horizontal Planes The method consists in determining the volumes of earth to be moved between the horizontal planes marked by successive contours. Thus, in fig. 25, the thin continuous lines represent the ground contours at 1m interval. The straight, parallel and equidistant lines (shown by broken lines) are drawn to represent the finished plane surface at the same interval. The point ‘P’ represent the points in which the ground contours and the grade contours of equal value intersect. By joining the p-points the line in which the proposed surface cuts the ground is obtained. These lines have been shown by thick lines. Along thin line no excavation or fill is necessary but within this line, excavation is necessary and outside this line filling is necessary. Thus, the extent of cutting between 17m ground contour and the corresponding 17m grade contour is shown by hatched lines. Similarly, the extent of cutting between the 16m ground contour and the corresponding 16m grade contour is also shown by hatched lines. Proceeding like this, we can mark the extent of earthwork between any two corresponding ground and grade contours and the areas enclosed in these extents can be measured by planimeter. The volume can then be calculated by using end area rule.
CHAPTER-6 Concrete Technology
___________________________________________________________________________ CHAPTER SIX ___________________________________________________________________________ CONCRETE TECHNOLOGY Back to contents page 6.1
Introduction Back to contents page Cement concrete is the most widely used structural material in the world for civil engineering projects. Its versatility, economy, adaptability, and worldwide availability, and especially its low maintenance requirements, make it very useful. It consists of cement, water, and aggregate which have been mixed together, placed, consolidated, and allowed to solidify and harden. The cement and water form a paste, which acts as the glue, or binder. When fine aggregate is added the resulting mixture is termed mortar. Then when coarse aggregate is included concrete is produced. Normal concrete consists of about three-fourths aggregate and one-fourth paste, by volume. The paste usually consists of water-cement ratios between 0.4 and 0.7 by weight. Admixtures are sometimes added for specific purposes, such as to entrain numerous microscopic air bubbles, impart colour, retard the initial set of the concrete, waterproof the concrete, etc. The operations involved in the production of concrete will vary with the type of end use for the concrete, but, in general, the operations,include the following (Fig.26) : a)
Batching the materials
b)
Mixing
c)
Transporting
d)
Placing
e)
Consolidating
f)
Finishing
g)
Curing
6.2
Proportioning Concrete Mixtures Back to contents page
For successful concrete utilization, the mixture must be properly proportioned. First, although it takes water to initiate the hydraulic reaction, the higher the water-cement ratio, the lower the resulting strength and durabilicy. Second, the more water that is used the higher will be the slump. Third, the more aggregate that is used, the lower the cost of the concrete. Fourth, the larger the maximum size of coarse aggregate, the less the amount of cement paste that will be needed to coat all the particles and provide necessary workability. Fifth, the more that concrete is consolidated, the better it becomes. Sixth, The use of properly entrained air enhances almost all concrete properties with little, or no, decrease in strength if the mix proportions are adjusted for the air. And seventh, the surface abrasion resistance of the concrete is almost entirely a function of the properties of the fine aggregate. 6.3
Fresh Concrete Back to contents page To the designer, fresh' concrete is of little importance. To the constructor, fresh concrete is all-important, because it is the fresh concrete that must be mixed, transported, placed, consolidated, finished, and cured. To satisfy both the designer and the constructor, the concrete should: a)
Be easily mixed and transported.
b)
Be uniform throughout, both within a given batch and between batches.
c)
Be of proper workability so that it can be consolidated, will completely fill the forms, will not segregate, and will finish properly.
The major property of importance to the constructor is the workability, which is difficult to define in precise terms. Like the terms warm and cold, workability depends upon the situation. One measure of workability is slump Table (1) below gives the recommended slump for various types of Concrete Construction. Table (1) Recommended slumps for various types of Construction Types of Construction
Slump (inch) Maximum
Minimum
1
1
1
1
Beams and reinforced walls
4
1
Building columns
4
1
Pavements and slabs
3
1
Mass concrete
2
1
Reinforced foundation walls and footings Plain footings, caissons, and substructure walls
6.4
Handling and Batching Concrete Materials Back to contents page Most concrete batches, although designed on the basis of absolute volumes of the ingredients, are ultimately controlled in the batching process on the basis of weight. Therefore it is necessary to know the weight volume relationships of all the ingredients. Then each ingredient must be accurately weighed if the resulting mixture is to have the desired properties. It is the function of the batching equipment to perform this weighing measurement.
(i)
Handling cement : Cement may be supplied to the project in paper bags, each containing 1 Cu ft. loose measure and weighing 94 lb net. However, for most large projects, the cement is supplied in bulk quantities from cement is supplied in bulk quantities from cement transport trucks, each holding 25 tons or more, or from railroad cars. Bag cement must be stored in a dry place on pallets and should be left in the original bags until used for concrete. If the batching of concrete requires one or more whole bags of cement, the use of bag cement simplifies the batching operation.
(ii)
Batching and concrete : Usually, concrete specifications require the concrete to be batched with aggregate having at least two size ranges (coarse and fine) and up to six ranges. (Fig. 27) illustrates the proper and improper methods of batching. Aggregate from each size range must be accurately measured. The aggregate, water, cement, and admixtures (if used) are introduced into a concrete mixer and mixed for a suitable period of time until all the ingredients are adequately blended together.
6.5
Batch plants and mixers Back to contents page There are two types of concrete-mixing operations in use, job-batched concrete and central-batched concrete. Today, unless/the project is in a remote location or is relatively large, more and more of the concrete is batched in a central batch plant and transported to the job site in ready-mixed concrete trucks. Fig. 28 shows a portable concrete batch plant, and Fig. 29 shows, a large central batch plant of the type in general use. A concrete batch required four different
sizes of coarse aggregate, plus sand, two types of cement and water. The water and liquid admixtures are normally measured by volume, while the cement and aggregates are measured by weight. To control the batching, close tolerances are maintained. Table (2) gives the permissible tolerances. are
available
in
Batch plants
three categories, manual, semiautomatic, and fully
automatic. Manual batching is generally used for small jobs or low output values (less than about 500 cu. yd total or around 20 cu. yd per hr). In semiautomatic plants the charging and discharging of the batches are activated manually but are automatically terminated. In a fully automatic batch plant, a single starter switch activates the batching sequence, the weights and volumes of which have been previously programmed into the system. Present-day plants usually have mixers capable of mixing up to 8 cu yd of concrete in each batch (although plants have been built with mixers capable of mixing 12 cu yd of concrete in each batch), and can produce up to about 200 cu yd of concrete per hour. The mixer either tilts to discharge the concrete into a truck or a chute is inserted into the mixer to catch and discharge the concrete. To increase efficiency, many large plants contain two mixers connected in series. The back mixer premixes the aggregates and cement, which reduces the time necessary for the front mixer to completely mix the batch.
Although the figures and discussion herein cover drum mixing of concrete, there are two other types of mixers in use-the pan mixer and the continuous mixer. In determining the quantities needed and the output for a given plant, any delays in productivity resulting from reduced operating factors should be included. Table (2) Recommended tolerances for batching concrete materials Batch weights greater than
Batch weights less than
30% of scale capacity Individual Ingredient batching Cumulative batching 1% or 0.3% of scale
batching batching Not less than required weight or
capacity, whichever is greater Not recommended 1
4% more than required weight Not recommended 1
Cement and other cementitious materials Water (by volume or weight), % Aggregates, %
30% of scale capacity Individual Cumulative
2
1
2
0.3% of scale capacity or 3% of required cumulative weight, whichever is
Admixtures (by volume
3
Not recommended
3
less Not recommended
or weight), %
6.6
Ready Mixed Concrete Back to contents page Concrete is mixed in a central location and transported to the purchaser in a fresh state, mixed at the plant or enroute. This type of concrete is termed ready mixed concrete, concrete purchased in this manner enjoys wide acceptance.
Obviously, to be useful, readymixed concrete must be available within a reasonable distance from the project. On remote sites and sites requiring large quantities of concrete, generally field concrete batch plants are used. Concrete purchased from a ready-mixed concrete plant can be provided in several ways. These include : a)
Central mixed concrete This is concrete which is completely in a stationary mixer and transported to the project either in a truck agitator, a truck mixer operating at agitating speed, or in a non agitating truck.
b)
Shrink-mixer concrete This is concrete which is partially mixed in a stationary mixer and then mixed completely in a truck mixer (usually en route to the project).
c)
Truck-mixer concrete This is concrete that is completely mixed in a truck mixer, with 70 to 100 revolutions to be at a speed sufficient to completely mix the concrete. This type of concrete is usually termed transit-mixed concrete because it is generally mixed en route. Transit mixers are available in several sizes up to about 14 cu yd, but the most popular size is 8 cu yd (fig.30). They are capable of thoroughly mixing the concrete within about 100 revolutions of the mixing drum at mixing speed (generally 8 to 12 rpm). This mixing during transit usually results a stiffening the mixture, and the addition of water is done at the job site to restore the slump, followed by remixing. This has caused problem and raised questions concerning the uniformity of ready-mixed concrete. Some of the water be withheld
until the mixer arrived at the project site (especially in hot weather), then the remaining water be added and an additional 30 revolutions of mixing be required. To offset any stiffening, small amounts of additional water are permitted, provided the design water-cement ratio is not exceeded. The uniformity requirements of ready mixed concrete are given in Table 3.
Table (3) Uniformity Requirements for Readymixed Concrete to be given Tests
Requirement,
expressed
as
maximum
permissible difference in results of tests of samples taken from two locations in the concrete batch Weight per cu ft calculated to an air-free
1.0 lb/cu. Ft.
basis Air content, volume percent of concrete
1.0%
Slump : If average slump is 4 in. or less
1.0 in.
If average slump is 4 to 6 in.
1.5 in.
Coarse aggregate content, portion by weight
6.0%
retained on No. 4 sieve Unit weight of air-free mortar based on
1.6%
average for all comparative samples tested Average compressive strength at 7 days for
7.5%
each sample, based on average strength of all comparative test specimens
Concrete may be ordered in several ways. They are : a)
Recipe batch The purchaser assumes responsibility for proportioning the concrete mixture, to include specifying the cement content, the maximum allowable water content, and the admixtures required. The purchaser may also specify the amounts and type of coarse and fine aggregate.
Under this approach, the purchaser assumes full responsibility for the resulting strength and durability of the mixture, providing the stipulated amounts are furnished as specified. b)
Performance batch The purchaser specifies the requirements for the strength of the concrete, and the manufacturer assumes full responsibility for the proportions of the various ingredients that go into the batch.
c)
Part performance and part recipe The purchaser generally specifies a minimum cement content, the required admixtures, and the strength requirements, allowing the manufacturer to proportion the concrete mixture within the constraints imposed. Today, most purchasers of concrete use the third approach, part performance and part recipe, as it ensures a minimum durability while still allowing the ready-mixed concrete supplier some flexibility to supply the most economical mixture.
6.7
Moving and Placing Concrete Back to contents page Once the concrete arrives at the project site, it must be moved to its final position without segregation and before it has achieved an initial set. This movement may be accomplished in several ways, depending upon the distance, elevation, and other constraints imposed. These methods include buckets or hoppers, chutes and drop pipes, belt conveyors and concrete pumps.
a)
Buckets or hoppers
Normally designed bottom dump buckets permit concrete placement at the lowest practical slump (Fig.31). Care should be exercised to prevent the concrete from segregating as a result of discharging from too high above the surface or allowing the fresh concrete to fall past obstructions. Gates should be designed so that they can be opened and closed at any time discharge of the concrete. b)
Manual or motor propelled buggies Hand buggies and wheelbarrows are usually capable of carrying from 4 to 9 cu ft of concrete, and thus are suitable on many projects, provided there are smooth and rigid runways upon, which to operate. Hand buggies are safer than wheelbarrows because they have two wheels rather than one. Hand buggers and wheelbarrows are recommended for distances less than 200 ft. while power-driven or motor driven buggies-with capacities up to around 14 cu ft., can traverse up to 1,000 ft economically (see Fig.32).
c)
Chutes and drop pipes Chutes are often used to transfer concrete from a higher elevation to a lower elevation. They should have a round bottom, and the slope should be steep enough for the concrete to -flow continuously without segregation. Drop pipes are circular pipes used to transfer the concrete vertically. The pipe should have a diameter at least eight times the maximum aggregate size at the top 6 to 8 ft, and may be tapered to approximately six times the maximum aggregate size. Drop pipes are usually used when concrete is placed in a wall or column to avoid segregation from allowing the concrete to free-fall through the reinforcement. In such areas, pipes should always be used.
d)
Belt conveyors Conveyors are classified into three types: (i) portable or self-contained conveyors; (ii) feeders or series conveyors; and (iii) side-discharge or spreader conveyors. All types must have the proper belt size and speed to achieve the desired rate of placement. Fig.33 shows the use of several portable conveyors to place concrete for a floor slab. This type of conveyor is capable of moving large quantities of concrete rapidly. Particular attention must be given to points where the concrete leaves one conveyor and either continues on another conveyor or is discharged, as segregation can easily occur. Conveyors lend themselves to moving concrete over long distances (Fig. 34) or up slopes (Fig.35). The major disadvantage is the time necessary to set them up and to change them. The optimum concrete slump for conveyors is from 2.5 to 3 inches.
e)
Concrete pumps The placement of concrete through rigid or flexible lines is not new. The pump is an extremely simple machine. By applying pressure to a column of fresh concrete in a pipe, it can be moved through the pipe if a lubricating outer layer is provided and if the mixture is properly proportioned for pumping. In order to work properly, the pump must be fed with concrete of uniform workability and consistency. Today, concrete pumping is one of the fastest growing specialty contracting fields. Pumps are available in a variety of sizes, capable of delivering concrete at sustained rates of 10 to 150 cu yd per hr. Effective pumping range varies from 300 to 1,000 ft horizontally, or 100 to 300 ft vertically, although occasionally pumps have moved concrete more than 5,000 ft horizontally and 1,000 ft vertically. Pumps require a steady supply of pumpable concrete to be effective. Today there are three types of pumps being manufactured: piston pumps, pneumatic pumps, and squeeze pressure pumps. They are shown diagrammatically in Fig. 36 (a), (b) and (c) , respectively. Most piston pumps today contain two pistons, with one retracting during the forward stroke of the other to give a more continuous flow of concrete. The pneumatic pumps normally use a reblending discharge box at the discharge end to bleed off the air and to prevent segregation and spraying. In squeeze pressure pumps, hydraulically powered rollers rotate on the flexible hose within the drum and squeeze the concrete out at the top. The vacuum keeps a steady supply of concrete in the tube from the receiving hopper.
Pumps may be mounted on trucks, trailers, or skids. The truck-mounted pump and boom combination is particularly efficient and cost-effective in saving labour and eliminating the need for pipelines to carry the concrete. Hydraulically operated and articulated. booms come in lengths up to 100 ft and more (Fig.36). Successful pumping of concrete is no accident. A common fallacy is to assume that any good placeable concrete will pump successfully. The basic principle of pumping is that the concrete moves as a cylinder through a lubricated line, with the lubrication continually being replenished by the cylinder of concrete. To pump concrete successfully, a number of rules should be carefully followed. They are : i)
Use a minimum cement factor of 517 Ib of cement per cubic yard of concrete (5.5 sacks per cu yd) .
ii)
Use a combined gradation of coarse and fine aggregate that ensures no gaps in sizes that will allow paste to be squeezed through the coarser particles under the pressures induced in. the line. In particular, it is important for the fine aggregate to have at lease 5 percent passing the No.100 sieve and about 3 percent passing the No. 200 sieve. Line pressures of 300 psi are common, and they can reach as high as 1,000 psi. This is the most often overlooked aspect of good pumping:
iii)
Use a minimum pipe diameter of 5 in.
iv)
Always lubricate the line with cement paste or mortar before beginning the pumping operation.
v)
Ensure a steady, uniform supply of concrete, with a slump of between 2 and 5 as and it enters the pump.
vi)
Always presoak the aggregates before mixing them in the concrete to prevent their soaking up mix water under the imposed pressure. This is especially important when aggregates are used which have a high absorption (such as structural lightweight aggregate).
vii)
Avoid the use of reducers in the conduit line. One common problem is the use of a 5-in to 4-in reducer at the discharge end so that workers will have only a 4 in, flexible hose to move around. This creates a obstruction and significantly raises the pressure necessary to pump the concrete.
viii)
Never use aluminum lines. Aluminium particles will be scraped from the inside of the pipe as the concrete moves through and will become part of the concrete. Aluminum and portland cement react, liberating hydrogen gas, which can rupture the concrete - with disastrous results.
6.8
Consolidating Concrete Back to contents page Concrete, being a heterogeneous mixture of water and solid particles in a stiff condition, will normally contain a large quantity, of voids when placed into the forms. It is the purpose of consolidation to remove these entrapped air voids. The importance of proper consolidation cannot be overemphasized, as entrapped air can render the concrete totally unstable. Entrapped air, can be reduced two ways - use more water or consolidate the concrete. Fig. 37 shows qualitatively the benefits of consolidation, especially on low-water -content concrete.
Consolidation is normally achieved through the use of mechanical vibrators. There are three general types : internal, surface and form vibrators. Internal or spud vibrators as they are often called, have a vibrating casing or head which is immersed into the concrete and vibrates at a high frequency (often as high as 10,000 to 15,000 vibrations per min) against the concrete. Currently these
vibrators are the rotary type and come in sizes from 3/4 in. to 7 in. (Fig. 38). They are powered by electric motors or compressed air. Manufacturers have extensive data on their vibrators. Surface vibrators exert their effects at the top surface of the concrete and consolidate the concrete from the top down. They are used mainly in slab construction, and there are four general types: the vibrating screed, the pantype vibrator, the plate or grid vibratory tamper, and the vibratory rolling screed. These surface vibrators operate in the range of 3,000 to 6,000 vibrations per min. Form vibrators are external vibrators attached to the outside of the form or mold. They vibrate the form, which in turn vibrates the concrete. These types of vibrators are generally used in large precast concrete plants. 6.9
Recommended vibration practices Back to contents page Internal vibration is generally best suited for ordinary construction provided the section is large enough for the vibrator to be manipulated. As each vibrator has an effective radius of action, vibrator insertions should be vertical at about 1.5 times the radius of action. The vibrator should never be used to move concrete laterally, as segregation can easily occur. The vibrator should be rapidly inserted to the bottom of the layer (usually 12 to 18 in. maximum lift thickness) and at least 6 in. into the previous layer. It should then be held stationary for about 5 to 15 sec until the consolidation is considered adequate. The vibrator should then be withdrawn slowly. Where several layers are being placed, each layer should be placed while the preceding layer is still plastic.
Vibration accomplishes two actions. First, it "slumps" the concrete, removing a large portion of air that is entrapped when the concrete is deposited. Then, continued vibration consolidates the concrete, removing most of the remaining entrapped air. Generally, it will not remove entrained air. The question concerning over vibration is often raised: When does it occur and how harmful is it? The fact is that on low-slump concrete (concrete with less than 3 in slump) it is almost impossible to overvibrate it with internal vibrators: When in doubt as to how much vibration to impart to low-slump concrete, vibrate it some more. The same cannot be said of concrete whose slump is 3 in. or more. This concrete can be overvibrated, which results in segregation as a result of coarse aggregate moving away from the vibrating head. Here the operator should note the pressure of air bubbles escaping to the concrete surface as the vibrator is inserted. When these bubbles cease, vibration is generally complete and the vibrator should be withdrawn. Another point of caution concerns surface vibrators. They too can overvibrate the concrete at the surface, significantly weakening it if they remain in one place too long.
Another concern is the vibration of reinforcing steel. Such vibration improves the bond between the reinforcing steel and the concrete/and thus is desirable. The undesirable side effects 'include damage to the vibrator and possible movement of the steel from its intended position. Finally, revibration is the process whereby the concrete is vibrated again after it has been allowed to remain undisturbed for some time. Such revibration can be accomplished at any time. The running vibrator will sink of its own weight into the concrete and liquefy it momentarily. Such revibration will i.-nprove the concrete through increased consolidation. 6.10
Finishing and Curing Concrete Back to contents page It cannot be stated too strongly that any work you do to a concrete surface after it has been consolidated will weaken the surface. All too often, concrete technicians overlook this fact and manipulate the surface of the concrete to produce a smooth, attractive surface. On walls and columns, an attractive surface may be desirable and the surface strength may not be too important, but on a floor slab, sidewalk, or pavement, the surface strength is very important. On the latter types of'surfaces only the absolute minimum finishing necessary to impart the desired texture should be permitted, and the use of "jitterbugging" (the forcing of coarse aggregate down into the concrete with a steel grate tool) should not be permitted, as the surface can be weakened significantly. Furthermore, each step in the finishing operation, from first floating to the final floating or troweling, should be delayed as long as possible and still permit the desired grade and surface smoothness to be obtained. In no
case should neat cement or mixtures of sand and cement be worked into such surfaces to dry them up. Along with placement and consolidation, proper curing of the concrete is extremely important. Curing may be considered as the method whereby the concrete is assured of adequate time, temperature, and supply of water for the cement to continue to hydrate. The time normally required is 3 days, and optimum temperatures are between 40 and 800F. As most concrete is batched with sufficient water for hydration, the only problem is to ensure that the concrete does not become dried out. This may be accomplished by ponding with water (for slabs), covering with burlap or polyethylene sheets or spraying with an approved curing compound. Curing is one of the least costly operations in the production of quality concrete, and one that is all too frequently overlooked. Concrete, if allowed to dry out during the curing stage, will attempt to shrink. The developing bonds from the cementitious reaction will attempt to restrain the shrinkage from taking place. But the end result is always the same: the shrinkage wins out and a crack forms as the shrinkage stress are always higher than the tensile strength of the concrete. Proper curing does reduce the detrimental effects of cracking and develops the intended strength of the concrete. 6.11
Placing Concrete in Cold Weather Back to contents page When concrete is placed in cold weather, some provision must be made to keep the concrete above freezing during the first few days after it has been placed. Specifications generally require that the concrete be kept at not less than 700F for 3 days or not less than 500F for 5 days after placement.
Preheating the water is generally the most effective method of providing the necessary temperature for placement. When the temperatures of the ingredients are known, the chart in Fig. 3 9 may be used to determine the temperature of concrete. A straight line across all three scales, passing through any two known tempera-tures, will permit the determination of the third temperature. If the sand is surface-dry, the solid lines of the scales giving the temperature of concrete should be used. However, if the sand contains about 3 percent moisture, the dotted lines should be used. 6.12
Placing Concrete in Hot Weather Back to contents page When the temperature of, fresh concrete exceeds" around 85 to 900F, the resulting strength and durability of the concrete can be reduced. Therefore most specifications require the concrete to be placed at a temperature less than 900F. When concrete is placed in hot weather, the ingredients should be cooled before mixing. Methods of cooling include using ice instead of water in the mix and cooling the aggregate with liquid nitrogen.
CHAPTER-7 Mechanised Construction
___________________________________________________________________________ CHAPTER SEVEN ___________________________________________________________________________ MECHANISED CONSTRUCTION Back to contents page 7.0
Introduction Back to contents page Mechanised construction involves the followings A.
Mechanised Construction Equipment and their applications.
B.
Work Study on Construction Equipment
C.
Plant Purchase Vs. Plant Hire
D. 7.1
a)
Investment Subsidy
b)
Establishment of Plant Hire Companies
Safety Programme.
Mechanical construction equipment & their applications Back to contents page Table (1) Application of Machinery & Equipment
Sl. No. 1.
Construction Equipment Air Compressors
Application Equipped with pavement breakers rock, steel and wood, circular and chain concrete vibrators etc.
2.
Cement Batching Plant
Batching Plant delivers properly proportioned batches of aggregate to dump trucks for delivery to construction sites.
3.
Crane
Lifting in field or shop
4.
Tractor Dozer
Bulldozer is the best equipment for excavation and construction of embankment where the lead is not more than 300 ft. Angle dozer should be used for side hill cuts for road in consolidated soil and rock rooters should be used to loosen material. Tractor dozer when used for jungle clearance will give better performance with tree felling attachment.
5.
Power showel, dragline back
Shovels used where excavation is above working
hoe, clamshell truck or
grade. Draglines and clamshells used where
crawler mounted
excavations are below working grade. Power shovel is most useful in two types deep face excavation. i)
Excavation in which material is cast
directly from cut to fill. Examples are side hill cuts for road and stripping thick over burden. ii)
Excavation involving long hauls by dump
trucks. Dragline can work below the work level or under water and is particularly suited for digging borrow pits excavating the mud and other saturated material. 6.
Rock drill, Pneumatic
Used to bore holes for explosives and to shatter and scale soft fractured rock.
7.
Towed scrapers
This equipment is economical where the haulage distance is from 300 ft. to 1500 ft. but haulage beyond 1500 ft. is not economical. As an expedient it can also be used to haul and spread aggregate.
8.
Concrete spreader
Spreads concrete into a continuous slab of concrete, leaving a uniformly level surface for the finisher.
9.
Concrete finisher
Follows spreader, consolidated and striking off final finished surface.
10.
Trucks
For
transportation
of
various
construction
material to job site. 11.
Trucks dump
Used for haulage of earth aggregates and other construction material.
12.
Tower cranes
Very
versatile
particularly
for
high
rise
construction
indispensable
for
mechanized
multistoreyed building construction.
13.
Truck mixers
a)
Luffing jib
b)
Trolley jib
Used for transportation of concrete from mixing plant to the laying site. Concrete transported can either be dry or wet.
14.
Hoists
For vertical transportation of building materials.
15.
Concrete vibrators
Used for compaction of concrete to prevent honey combing. These can either be –
16.
Bar benders and croppers
a)
Air driven
b)
Petrol engine driven
c)
Electric driven
Used for bending of various steel sections into required shape for R.C.C. construction.
17.
7.2
Pumps
For pumping of water, sewage etc.
Work Study on construction equipment Back to contents page
7.2.1
The work study on construction equipment is very important so as to economise in “STEMP”.
7.2.2
S
=
Space
T
=
Time
E
=
Effort
M
=
Materials
P
=
Power
Time and motion study on the use of construction equipment at each construction site is to be carried out so as to reduce the cycle time of operation to the barest minimum and result in increased productivity.
7.2.3
In due course, a library of production outputs with various types of plant and machineries for different applications can be worked cut, which can then be used for tendering purposes.
7.3
Plant Purchase versus Plant Hire
Back to contents page Since the purchase of construction plant and equipment involves considerable capital outlay, judicious decision is to be taken on purchase of construction plant versus plant hire at various sites of work. Needless to mention, for large jobs involving spread over number of years, it may be ultimately economical to buy the equipment but for jobs involving short term use, plant hire is more economical. There are two issues which must be highlighted in this connection. 7.3.1
Investment subsidy Unfortunately, in our country, no investment subsidy is given by the Government to contractors or plant owners. Even in an advanced country like U.K., the Government gives subsidy to extent of 45% of the cost of the plant in underdeveloped areas and 25% of the cost of the plant elsewhere as out right grant. There is, therefore, considerable incentive to the builders to go in for mechanization which results in up-gradation of technology and better quality of work.
7.3.2
Establishment of Plant Hire companies The concept of plant hire companies on a large scale has still not caught up in our country. Abroad, it is very common for individual entrepreneurs to own a few contracts’ Plant and Machinery and give them on hire to prospective builders. In fact, young engineering graduates and private entrepreneurs should be encouraged to come out in this profession of owing contractors’ plant and machinery and rent them out to contracting Companies and Builders. In a small country like Cyprus, there are three private parties owning and running ready mix concrete plants and they are in business of selling RMC to
contracting companies/builders. There is tremendous scope for plant hire companies to be established in the country. Infact large contracting companies like NBCC, NPCC etc. owing their own construction plant and equipment can open a plant hire cell so as to rent out the equipment during lean period and run it as a profit centre. 7.4
Safety Programme Back to contents page
7.4.1
Accidents just do not happen. There are caused. One must remender that “danger begins where safety ends”.
7.4.2
In case of mechanized construction, there is all the more need for following added safety measures. Some of these are given below : a)
When heavy equipment like tractor, bulldozers and motorized scapers are in operation, only one person, the operator should be permitted to ride – accidental fall of any other person can be fatal.
b)
When tractor dozer is parked, the blade should not be left in raised position – accidental fall can crush people underneath.
c)
During movement of dozers, the blade should be carried low for better visibility.
d)
People should not be allowed to travel in a tipper truck body. In case of accidental operation of tipping lever, people can, be ejected out of a moving tipper resulting in serious accidents.
e)
All equipment to be driven by authorized operators only.
f)
During maintenance, always support raised piece of equipment on wooden sleepers etc. by solid support, rather than depending on hydraulic jacks only.
g) 7.5
Ensure use of protective clothings and accessories.
Why mechanical construction equipment? Back to contents page a)
To cut down cost of construction.
b)
To accelerate the speed of work.
c)
To ensure quality control.
d)
To eliminate human elements involved.
Following essential requirements should be met : a)
Proper selection of equipments.
b)
The work is planned for use of machinery and equipment.
c)
The plant is correctly maintained and preventive maintenance carried out deligently.
7.6
d)
The plant engineer knows his job.
e)
The plant operator does his job well.
Production Out Puts Back to contents page Table (2) Production Out Puts
Sl. No.
Equipment
Lead
Production Out Put
1.
D-8-H Bulldozer
50 Meter
700 Cubic meters per day
2.
D-8-H Bulldozer
100 Meter
400 cubic Meters per day
3.
Towed Scraper
500 Meter
250 Cubic Meter per day
4.
Scoop loader and 10 Kilo Meters
34 cubic meter per day
10 tippers
7.7
Production Trial Back to contents page
Table (2) Production Trial on 16”x9” Jaw Crushers Sl. No.
Item Description
Production Capacity
1.
Dust
2.20 Cubic meter per crusher per day.
2.
6 mm Chips
2.02 Cubic Meter per crusher per day.
3.
10 mm Chips
4.06 cubic meter per crusher per day
4.
Over sized up to 40 mm
8.27 cubic meter per crusher per day Total = 16.55 cubic meter per day
7.8
Economic Life Back to contents page Table (4) Economic Life Machines
Sl. No.
Name of Machine
Years
Kms/Hours
1.
Road rollers
15
12,000 hrs.
2.
Truck tipper
12
2,40,000 kas
3.
Dumper
12
10,000 hrs.
4.
Stone crusher (electrical)
15
12,000 hrs.
5.
Stone crusher (diesel)
12
10,000 hrs.
6.
Hot mix plant
12
9,000 hrs.
7.
Paver finisher
15
9,000 hrs.
8.
Scoop loader
15
9,000 hrs.
9.
Wheeled dozer
15
9,000 hrs.
10.
Crawler dozer
15
9,000 hrs.
11.
Motorised/Tower scrapper
15
9,000 hrs.
12.
Motor Grader
15
9,000 hrs.
13.
Portable Generator
12
10,000 hrs.
14.
Diesel welding set
15
10,000 hrs.
15.
Pumping set Diesel
8
-
16.
Jeep/Car/Mini Bus
10
2,00,000 kas
17.
Mobile Crane
15
8,000 hrs
18.
Vibrators
5
-
19.
Concrete mixers
6
-
20.
Air Compressor
12
9,000 hrs.
CHAPTER-8 Standard Field Quality Plan
___________________________________________________________________________ CHAPTER EIGHT STANDARD FIELD QUALITY PLAN
8.0 STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : SURVEY & SOIL INVESTIGATION Sl. No.
1.
Component/Operation & Description of Test
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
a)
DETAILED SURVEY & ALIGNMENT Field Survey
100%
Route map & measurement schedules
Contractor
b)
Plotting of Route
100%
Contractor
c)
Profile Plotting
100%
Field book, POWERGRID Technical Specification & Geographical maps. Approved Sag template & approved profile drawings.
d)
Tower Spotting
100%
Contractor
e)
Tower Schedule
100%
Tower Spotting Data & POWERGRID technical specification Approved profile drawings & route alignment
Contractor
Contractor
2.
CHECK SURVEY
a)
Bisection of Angle/Accuracy of alignment
100%
Approved profile drawings & route alignment
Contractor
b)
Check for profile levels and electrical & other clearances
100%
Approved profile drawings
Contractor
c)
Check for span marking and lengths
100%
d)
Check for tower type and position as per site conditions Estimation of benching & Revetment volumes (As per site conditions) Final profile & Tower Schedule
100%
Approved profile drawings POWERGRID technical specification Approved profile drawings POWERGRID technical specification Approved profile drawings POWERGRID technical specification Approved profile drawings POWERGRID technical specification
e) f) 3.
SOIL INVESTIGATION
A)
AT NORMAL LOCATIONS
100% 100%
&
Contractor
&
Contractor
&
Contractor
&
Contractor
Remarks
Check
Approval by POWERGRI D Approval by POWERGRI D Approval by POWERGRI D Approval by POWERGRI D Approval by POWERGRI D
B
Approval by POWERGRI D Approval by POWERGRI D Approval by POWERGRI D Approval by POWERGRI D Approval by POWERGRI D Approval by POWERGRI D
B
B B B B
B B B B B
i)
Borelog/Trial pit
All other than angle, river crossing & special locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRID approved lab.
Approval by POWERGRI D. POWERGRI D to witness for a min. 25% of locations
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : SURVEY & SOIL INVESTIGATION Sl. No.
Component/Operation & Description of Test
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
ii)
Ground Water level
All other than angle, river crossing & special locations
POWERGRID technical specificatin & relevant IS
Contractor
Approval by POWERGRID. POWERGRID to witness for a min. 25% of locations.
B
iii)
Classification of foundations (based on soil classification, liquid limit, swell index & ground water level)
All other than angle, river crossing & special locations
POWERGRID technical specification & relevant IS
Contractor
Approval by POWERGRID
B
B)
AT ANGLE TOWER LOCATIONS (Min. one location in 4 kms. Stretch)
i)
Borelog
All angle tower locations
POWERGRID technical specification & relevant IS
Contractor/P OWERGRID approved lab
Approval by POWERGRID
B
ii)
Standard Penetration Test
All angle tower locations
POWERGRID technical specification & relevant IS
Contractor
Approval by POWERGRID
B
iii)
Gradation
All angle tower locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRI D approved lab.
Approval by POWERGRID
B
iv)
Rock drilling wherever applicable
All angle tower locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRI D approved lab
Approval by POWERGRID
B
v)
Chemical Analysis of subsoil
All angle tower locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRI D approved lab
Approval by POWERGRID
B
vi)
Bearing Capacity
All angle tower locations
POWERGRID technical specification & relevant IS
Contractor
Approval by POWERGRID
B
vii)
Classification of foundation
All angle tower locations
POWERGRID technical specification & relevant IS
Contractor
Approval by POWERGRID
B
C)
AT RIVER CROSSING AND SPECIAL LOCATIONS
i)
Borelog
At River Crossing & Special Locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRI D approved lab
Approval by POWERGRID
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : SURVEY & SOIL INVESTIGATION Sl. No.
Component/Operatio n & Description of Test
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
ii)
Standard Penetration Test
At River Crossing & Special Locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
iii)
Gradation
At River Crossing & Special Locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
iv)
Rock drilling wherever applicable
At River Crossing & Special Locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
v)
Ground Water Level
At River Crossing & Special Locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
vi)
Chemical Analysis of sub-soil
At River Crossing & Special Locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
vii)
Dynamic Cone Penetration Test
At River Crossing & Special Locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
viii)
Vane Shear Test (Where UDS is not possible)
At River Crossing & Special Locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
ix)
Bearing Capacity
At River Crossing & Special Locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
x)
Souring depth & velocity of river
At mid stream locations
POWERGRID technical specification & relevant IS
Contractor
Approval by POWERGRID
B
xi)
Highest flood level
At mid stream locations
POWERGRID technical specification & relevant IS
Contractor
Approval by POWERGRID
B
xii)
Classification of foundations
At River Crossing & Special Locations
POWERGRID technical specification & relevant IS
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
D.
SOIL RESISTIVITY
All locations
IS : 2131, IS : 2720 and POWERGRID specifications
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : SURVEY & SOIL INVESTIGATION Sl. No.
Component/Operation & Description of Test
E.
TEST ON SOIL AND ROCK SAMPLES
a)
Tests on undisturbed and disturbed samples
i)
Visual and Engineering Classifications
ii)
Sieve Analysis and Hydrometer Analysis
iii)
Liquid, Plastic and Shrinkage limits
iv)
Specific gravity
v)
Chemical analysis
vi)
Swell pressure and free swell Index Determination
vii)
Proctor compaction test
b)
Tests on undisturbed and disturbed samples
i)
Bulk density & moisture content
ii)
Relative density (for sand)
iii)
Unconfined compression Test
iv)
Box shear test (in case of sand)
v)
Triaxial shear Test a) Unconsolidated undrained b) Consolidated drained test c)
Consolidation
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
All angle tower locations, river crossing and special locations
IS : 2131, IS : 2720 & POWERGRID specifications
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
All angle tower locations, river crossing and special locations
IS : 2131, IS : 2720 & POWERGRID Specifications
Contractor/ POWERGRID approved lab
Approval by POWERGRID
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : SURVEY & SOIL INVESTIGATION Sl. No.
Component/Operation & Description of Test
c)
Tests on Rock
i)
Visual Classification
ii)
Moisture Content, Porosity and density
iii)
Specific Gravity
iv)
Hardness
v)
Slake durability
vi)
Unconfined compression test
vii)
Point Load strength index
viii)
Deformability test
d)
Chemical analysis of subsoil water
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
All angle tower locations, river crossing and special locations
IS : 2131, IS : 2720 & POWERGRID specifications
Contractor/ POWERGRID approved lab.
Approval by POWERGRI D
B
All angle tower locations, river crossing and special Locations
IS : 2131, IS : 2720 & POWERGRID Specifications
Contractor/ POWERGRID approved lab
Approval by POWERGRI D
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FOUNDATION MATERIALS Sl. No.
Component/Operation & Description of Test
4.
CHECKING OF FOUNDATION MATERIALS
A)
CEMENT
i)
Fineness
ii)
Compressive Strength
iii)
Initial & final setting time
iv)
Soundness
v)
Heat of Hydration for low heat cement (Not Applicable for OPC & PPC)
vi)
Chemical Composition of Cement
B)
COARSE AGGREGATES
i) ii)
Determination of Particle size (Sieve Analysis)
iii)
Flakiness Index
iv)
Crushing Value
v)
Specific Gravity*
vi)
Bulk Density*
vii)
Absorption Value*
viii)
Moisture Content*
ix)
Soundness of Aggregate**
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
One sample per lot of 100 MT or part thereof from each source for MTCs and one sample per lot of 200 MT or part thereof from each source for site testing
IS : 456, IS : 4031, IS : 269, IS : 8112, IS : 12269, IS : 1489 & POWERGRID Specification.
Manufacturer/ POWERGRID approved lab
Review of manufactu-rers test certificates (MTCs) and laboratory test results by POWERGRID
B
One sample per lot of 100 MT or part thereof from each source for MTCs.
IS : 456, IS : 4031, IS : 269, IS : 8112, IS : 12269, IS : 1489 & POWERGRID specification
Manufacturer
Review of manufactu-rers test certificates by POWERGRID
B
One sample per lot of 200 cubic meter or part thereof from each source for each size
IS : 383, IS : 2386 and POWERGRID specification
POWERGRID approved lab
Each source to be approved by POWERGRID. Review and acceptance of test result by POWERGRID.
B
Presence of deterious materials
* Applicable to design mix concretes only. ** Applicable to concrete work subject to frost action.
Check
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FOUNDATION MATERIALS Sl. No.
Component/Operatio n & Description of Test
C)
FINE AGGREGATE
i)
Gradation/Determinatio n of Particle size (Sieve Analysis)
ii) iii) iv) v) vi) vi)
Specific Gravity and density*
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
One sample per lot of 200 cubic meter or part thereof from each source
IS : 383, IS : 2386, IS : 4031, IS : 236, IS : 456 and POWERGRID Specification
POWERGRI D approved lab
Each source to be approved by POWERGRID. Review and acceptance of test result by POWERGRID
B
Moisture Content* Absorption Value* Builking* Silt Content Test Presence of deleterious materials
D)
WATER
i)
Cleanliness (Visual Check)
100%
IS : 456, IS : 3205 and POWERGRID specification. The water used for mixing concrete shall be fresh, clean and free from oil, acids and alkalies, organic materials, or other deleterious materials
Contractor
Each source to be approved by POWERGRID
C
ii)
Suitability of water for RCC work
One sample per source
POWERGRID specification. Potable water is generally suitable for concreting.
Contractor
Certification regarding potability of water by contractor and approval by POWERGRID
B
iii)
P.H. Value
One sample per source
IS : 456, IS : 3025 and POWERGRID specification. Min. 6. Max. 8.
POWERGRI D approved lab/Contracto r
Approval by POWERGRID
E)
REINFORCEMENT STEEL
i)
Identification & size
Random
IS : 432, IS : 1139, IS : 1786 & POWERGRID specification
Contractor
Approval by POWERGRID
* Applicable to design mix concretes only. ** Applicable to concrete work subject to frost action.
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FOUNDATION MATERIALS Sl. No.
Component/Opera tion & Description of Test
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
ii)
Chemical Analysis Test
One sample per heat
IS : 432, IS : 1139, IS : 1786 & POWERGRID specification
Manufacturer
Review of Manufacturers test certificates by POWERGRID
B
iii)
Tensile Test Yield Stress/proof stress
One sample per lot of 40 MT or part thereof for each size of steel conforming to IS : 1139 and 5 MT or part thereof for HDS wire for each size of steel as per IS : 432. For steel as per IS : 1786 under 10 mm 1 sample for each 25 MT or part thereof. 10 mm – 16 mm 1 sample for each 35 MT or part thereof. Over 16 mm 1 sample for each 45 MT or part thereof.
IS : 432, IS : 1139, IS : 1786 & POWERGRID specification
Manufacturers/ POWERGRID approved lab
Review of manufacturers test certificates as well as lab test result by POWERGRID
B
iv)
One sample per lot of 5 MT or part thereof for each size
IS : 432 POWERGRID specification
Manufacturer/POWERGRID appro-ved lab
Review of manufactu-rers test certificates as well as lab test result by POWERGRID
B
100%
POWERGRID approved drawing & specification
Contractor
Approval by POWERGRID
C
v)
Percentage Elongation
vii)
Reverse Bend Test for HDS wire
F)
EARTHING MATERIALS
i)
Identification, cleanliness & Galvanising defects
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FOUNDATION Sl. No.
Component/Operation & Description of Test
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
5.
TOWER FOUNDATION
A)
BEFORE EXCAVATION
i)
Checking of pegs condition as per line and alignment
100% on each location
IS : 4019, IS : 5613 & POWERGRID approved drawings/specification.
Contractor
Approval by POWERGRID
C
ii)
Checking of pit making as per drawings & RL
100% on each location
IS : 4019, IS : 5613 & POWERGRID approved drawings/specification.
Contractor
Approval by POWERGRID
C
B)
EXCAVATION
i)
Dimensional conformity
Each location
IS : 4019, IS : 5613 & POWERGRID approved drawings/specification.
Contractor
Approval by POWERGRID
B
ii)
Verticality & Squareness of each pit
Each location
IS : 4019, IS : 5613 & POWERGRID approved drawings/specification.
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
iii)
Verification of classification of foundation
Each location
IS : 4019, IS : 5613 & POWERGRID approved drawings/specification.
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
C)
STUB & TEMPLATE
i)
Identification & Assembly
100% on each location
POWERGRID approved drawings/specification.
Joint Inspection by POWERGRID and contractor
Approval/ clearance by POWERGRID
C
ii)
Template level, width & diagonal
100% on each location
POWERGRID approved drawings/specifications
Joint Inspection by POWERGRID and contractor
Approval/ clearance by POWERGRID
B
iii)
Tightening of all bolts & nuts of template, stubs & cleats
100% on each location
POWERGRID approved drawings/specification.
Joint Inspection by POWERGRID and contractor
Approval/ clearance by POWERGRID
C
iv)
Stub setting
100% on each location
POWERGRID approved drawings/specification
Joint Inspection by POWERGRID and contractor
Approval/ clearance by POWERGRID
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FOUNDATION Sl. No.
Component/Operatio n & Description of Test
D)
P.C.C. Padding
E)
STAGING FOR RAISED CHIMNEY
i)
Check durability, strength & soundness of staging, joints adequacy of its joints & specific levels
F)
SHUTTERING (Formwork)
i)
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
For all locations
IS : 456 and POWERGRID approved foundation drawings & specification
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
100%
POWERGRID Specification
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
Check for materials, breakage or damage
100%
POWERGRID Specification/appr oved drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
ii)
Check for plumb alignment, parallelism, squareness and equidistance from stub.
100% before casting
POWERGRID Specification/appr oved drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
iii)
Dimensional check
100% before casting
POWERGRID Specification/appr oved drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
iv)
Check for level & height
100% before casting
POWERGRID Specification/appr oved drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
v)
Check for rigidity of frame/tightness
100%
POWERGRID Specification/appr oved drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
vi)
Cleaning and oiling
100%
POWERGRID Specification/appr oved drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FOUNDATION Sl. No.
Component/Operation & Description of Test
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
vii)
Diagonal bracing if required as per drawings/site conditions
100%
POWERGRID Specification/approv ed drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
viii)
Checking of joints to avoid undue loss of cement slurry
100%
POWERGRID Specification/approv ed drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
G)
PLACEMENT OF REINFORCEMENT STEEL
i)
Check the steel bars for rust, cracks, surface flaws, laminate etc. (Visual check)
100%
IS : 456 and POWERGRID Specification/approv ed drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
ii)
Check as per the bar bending schedule before placement of concrete
For all locations
IS : 456 and POWERGRID Specification/approv ed drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
iii)
Check cutting tolerance for bars as per check list/drawings.
For all locations
IS : 456 and POWERGRID Specification/approv ed drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
Check whether all the bent bars and lap lengths are as per approved bar bending schedule iv)
Check whether all joints & crossing of bars are tied properly with right guage & annealed wire as per specification
100%
IS : 456 and POWERGRID Specification/approv ed drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
v)
Check for proper cover distance, spacing of bars, spacers & chairs after the reinforcement cage has been put inside the formwork
100%
IS : 456 and POWERGRID Specification/approv ed drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
vi)
Check whether lapping of bars are tied properly with right guage and annealed wire as per specification
100%
IS : 456 and POWERGRID Specification/approv ed drawings
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FOUNDATION Sl. No.
Component/Operation & Description of Test
H.
PILE FOUNDATION (additional Tests) (For normal tower foundations)
i)
Checking of centre line of pile group
ii)
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
Each pile group
IS : 2911 & POWERGRID approved pile foundation drawings/specificatio n.
Joint Inspection by POWERGRID and contractor
Checklist to be prepared and signed jointly
B
Check pile location
Each pile
IS : 2911 & POWERGRID approved pile foundation drawings/specificatio n.
Joint Inspection by POWERGRID and contractor
Checklist to be prepared and signed jointly
B
iii)
Temporary casing tube & permanent liner also check thickness of liner material (if applicable)
Each pile
IS : 2911 & POWERGRID approved pile foundation drawings/specificatio n.
Joint Inspection by POWERGRID and contractor
Verticality of the tube to be checked
B
iv)
Bentonite slurry (if applicable)
Each pile
IS : 2911 & POWERGRID approved pile foundation drawings/specificatio n.
Joint Inspection by POWERGRID and contractor
Records to be kept by POWERGRID for specific gravity of slurry
B
v)
Pile depth, level, size and alignment
Each pile
IS : 2911 & POWERGRID approved pile foundation drawings/specificatio n.
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
A
vi)
Chipping of pile head
Each pile
IS : 2911 & POWERGRID approved pile foundation drawings/specificatio n.
Joint Inspection by POWERGRID and contractor
Before concreting pile cap, pile head to be chipped off for concreting
B
Vii)
Standard Penetration Test
As per POWERG RID BOQ/ Specificatio n
IS : 2911 & POWERGRID approved pile foundation drawings/specificatio n.
Joint Inspection by POWERGRID and contractor
Records to be kept by POWERGRID. Approval by POWERGRID.
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FOUNDATION Sl. No.
Viii)
Component/Operation & Description of Test Pile load testing
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
As per POWERGRI D BOQ/Specification
IS : 2911 & POWERGRID approved pile foundation drawings/specification.
Joint Inspection by POWERGRID and contractor
Records to be kept by POWER-GRID. Approval by POWER-GRID.
B
ix)
Anchor bolts if applicable
a)
Level, centre to centre distance of bolts
100% on each location
POWERGRID approved pile foundation drawings/specification
Joint Inspection by POWERGRID and contractor
Checklist to be prepared and signed jointly
B
b)
Visual check for galvanising
100% on each location
POWERGRID approved pile foundation drawings/specification
Joint Inspection by POWERGRID and contractor
Checklist to be prepared and signed jointly
B
100%
IS : 456 and POWERGRID approved drawings and specifications.
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
100%
IS : 456 and POWERGRID approved drawings and specifications.
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
100%
IS : 456 and POWERGRID approved drawings and specifications.
Joint Inspection by POWERGRID and contractor
Min. gap between boxes and reinforcement bars should be maintained. Approval by POWERGRID
C
One sample per location
IS : 456, IS : 516, IS : 1199 and POWERGRID specifications.
Contractor
Approval by POWERGRID
B
6. A)
B)
C)
D) i)
CONCRETING BATCHING, MIXING & PLACING OF CONCRETE AND COMPACTING FIXING OF CHIMNEY COLUMN Check for Width/length, squareness, parallelism & equidistance from stub PLACING CONCRETE, POKING AND COMPACTING
CONCRETE TESTING Slump Test
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FOUNDATION Sl. No. ii)
E)
F) i) ii) G) i)
ii)
Component/Operation & Description of Test
Check for quantities for cement, fine aggregate, coarse aggregate and water while batching CHECK FINISHING, DIMENSIONAL CONFORMITY AND WORKMANSHIP BEFORE & AFTER BOX REMOVAL BACKFILLING Check for thickness of layer & watering Check for compaction/ramming REVETMENT Size of stone for Revetment (Stones with round surface shall not be used) Moisture content for Revetment stone
H)
Check for Weep holes and Bond stones in Revetment COPING
I)
CURING
J)
EARTHING (Pipe or counter poise type)
iii)
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
100% on all locations
IS : 456, IS : 516, IS : 1199 and POWERGRID specifications.
Contractor
Checklist to be prepared and signed jointly
B
100%
IS : 456, IS : 516, IS : 1199 and POWERGRID specifications.
Contractor
Checklist to be prepared and signed jointly
B
100%
POWERGRID Specification
Contractor
Approval by POWERGRID
C
100%
POWERGRID Specification
Contractor
Approval by POWERGRID
C
100%
POWERGRID specification & approved drawings.
Contractor
Approval by POWERGRID
C
One sample per source
IS : 1124 Max. 5%
POWERGRI D approved lab
Approval by POWERGRID
B
100%
POWERGRID Specification/approved drawings/IS : 1597
Contractor
Approval by POWERGRID
C
100% on all location
POWERGRID Specification
Contractor
Approval by POWERGRID
B
100% on all location
POWERGRID Specification
Contractor
Approval by POWERGRID
C
100%
IS : 5613 and POWERGRID Specification
Contractor
Approval by POWERGRID
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FOUNDATION Sl. No.
K) i)
Component/Operati on & Description of Test
CONCRETE CUBE TESTING Compressive Strength
Sampling Plan with basis
a) One sample locations (One sample consists of min. 3 test cubes for 28 days strength)
Ref. Document & acceptance norm
Testing Agency
Compressive Strength for concrete of pile cap, beams, chimney etc.
One sample for every 20 Cum of concrete or part thereof for each days of concreting
Check
IS : 1199, IS : 456, IS : 516 and POWERGRID Specification
POWERGRID approved lab
Approval by POWERGRID Cubes must be tested within a week after 28 days curing period and test results should be approved before tower erection
A
IS : 1199, IS : 456, IS : 516 and POWERGRID Specification
POWERGRID approved lab
-do-
A
b) For pile foundation one sample for each pile
ii)
Remarks
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : ERECTION Sl. No.
7. A) i)
ii)
B) i)
ii)
Component/Operation & Description of Test
TOWER ERECTION MATERIAL CHECKING Visual checking of tower members for damage, cleanliness, galvanising and stacking Visual checking of galvanised bolts and nuts, step bolts, D-shackles, Ubolts, spring washers & enamelled plates ERECTION OF SUPER STRUCTURE Tightness of bolts, identification, cleanliness & galvanising Punching of tightned bolts
iii)
Checking of assembly and verticality
iv)
Tack welding
v)
Tower footing resistance
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
100%
IS : 5613 and POWERGRID approved drawings/specification
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
C
100%
IS : 5613 and POWERGRID approved drawings/specification
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
C
100% on each location
POWERGRID approved drawings/specification
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
C
100% on each location
POWERGRID approved drawings/specification
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
C
100% on each location
POWERGRID approved drawings/specification
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
B
100% on each location
POWERGRID approved drawings/specification
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
B
100% on each location
POWERGRID approved drawings/specification
Joint Inspection by POWERGRID and contractor
Record to be kept for tower footing resistance before and after earthing
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : ERECTION Sl. No. vi)
8. A) i)
ii) B)
Component/Operation & Description of Test
Fixing of danger plate, number plate, phase plates & circuit plate as applicable LINE STRINGING Insulator Checking Visual checking of Insulators (Indentification, cleanliness, glazing, cracks & white spots) IR Measurement Visual Checking of Conductor and Earthwire
i)
Visual checking of hardware fittings (identification, cleanliness, galvanising and mechanical damages) Identification, cleanliness & packing Damage of Conductor & Earthwire Drum rubbing against ground or any metal part Conductor & Earthwire Stringing Initial conductor position
ii)
Check for temperature
C)
i) ii) iii) D)
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
100% on each location
POWERGRID approved drawings/specification
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
C
100%
IS : 5613 & POWERGRID approved drawings/specification s
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
100%
POWERGRID specification
-do-
-do-
B
100%
IS : 5613 & POWERGRID approved drawings/specification s
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
100%
IS : 5613 & POWERGRID approved drawings/specification s
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
C
Entire route
IS : 5613 & POWERGRID approved SAG & Tension Charts and Specifications
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
Entire route
IS : 5613 & POWERGRID approved SAG & Tension Charts and Specifications
Joint Inspection by POWERGRID and contractor
Approval by POWERGRID
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : ERECTION Sl. No. iii)
a) b) c) iv)
v)
9. a)
b)
c)
d) e)
Component/Operation & Description of Test
Final Conductor & Earthwire Position Electrical Clearances Sag/Tension for conductor & earthwire Joints in conductor and earthwire Jumpering Fixing of pilot insulator string (if any) FINAL CHECKING Check for the completion of backfilling & leftover materials Fixing of ACD & all tower accessories Tightening, punching and tack welding of bolts Final ground and electrical clearances Earthing
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
Check
Entire route
IS : 5613 & POWERGRID approved SAG & Tension Charts and Specifications
Joint Inspection by POWERGRID and contractor
Records to be kept duly signed by POWERGRID and contractor
B
Entire route
IS : 5613 & POWERGRID approved SAG & Tension Charts and Specifications
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
B
Entire route
IS : 5613 & POWERGRID approved SAG & Tension Charts and Specifications
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
B
100%
IS : 5613 & POWERGRID approved drawings/specifications
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
B
Entire route
IS : 5613 & POWERGRID approved drawings/Specifications
Joint Inspection by POWERGRID and contractor
Check list to be prepared and signed jointly
B
STANDARD FIELD QUALITY PLAN FOR TRANSMISSION LINE PACKAGES Section : FINAL TESTING & PRE-COMMISSIONING Sl. No.
10.
11.
Component/Operation & Description of Test
MEGGAR TEST
FINAL TESTING & PRECOMMISSIONI NG ON LINE
Sampling Plan with basis
Ref. Document & acceptance norm
Testing Agency
Remarks
100%
POWERGRID latest PreCommissioning procedures (Doc. No. D-2-01-70-01-00)
Joint Inspection by POWERGRID and contractor
Records to be kept duly signed by POWERGRID and contractor
A
100%
POWERGRID latest PreCommissioning Procedures (Doc. No. D-201-70-0-00)
Joint Inspection by POWERGRID and contractor
Records to be kept duly signed by POWERGRID and contractor
A
Section : GENERAL GUIDELINES FOR IMPLEMENTATION 1.
Details of categories of check codes A, B & C including accepting and deviation dispositioning authorities are indicated at Annexure-I.
2.
POWERGRID specification shall mean POWERGRID technical specification, approved drawings/data sheets and LOA provisions applicable for the specific contract.
Check
3.
Acceptance criteria and permissible limits for certain tests are indicated at Annexure-II. For balance tests, site to verify the same with respect to POWERGRID specification, relevant Indian Standards and/or prevalent code of practice.
4.
It is clarified that the tests indicated at column 2 of this FQP i.e. against column "Component operation & Description of Test," are only generally required to be conducted. However, POWERGRID reserves the right to carry-out any additional tests at any stage if the situation so warrants.
5.
POWERGRID site representative shall witness all the tests conducted by the contractor as mentioned in this FQP. However, in case of tests conducted in the POWERGRID approved lab, it is preferred to witness the tests in the lab itself, if possible.
6.
Head of GHQ shall approve testing laboratory before accepting the test results from the lab.
7.
Head of GHQ shall approve the sources for cement, coarse aggregate, fine aggregate & water before actual utilisation.
8.
All the testing & measuring equipments used by the contractor for testing are required to be calibrated. A copy of valid calibration report shall be retained by POWERGRID as records.
9.
Classification of foundations shall be approved by POWERGRID based on the Joint Inspection Report & soil investigation reports.
10.
Curing of concrete work should be continued for a minimum period of 10 days.
11.
Zone-IV fine aggregate shall not be used for concreting work.
Section : GENERAL GUIDELINES FOR IMPLEMENTATION 12.
Identification and traceability records in the standard formats for various materials in line with QA&I circular dated 7-5-96 shall be maintained and retained in POWERGRID.
13.
CEMENT
13.1
In case supply of cement is in the scope of the contractor, the same shall be procured from sources approved by POWERGRID site and got tested at site on sample basis for specified acceptance tests as specified in this FQP at a reputed Third Party Lab approved by POWERGRID site.
13.2
The samples of cement for site testing shall be taken within three weeks of the delivery and all the tests shall be commenced within one week of sampling.
14.
REINFORCEMENT STEEL
14.1
In case supply of reinforcement steel is in the scope of the contractor, the same shall be procured from the main producers i.e. SAIL, TISCO, IISCO or Rashtriya Ispat Nigam or the rerollers approved by main producers. The reinforcement steel shall be got tested at site on sample basis for specified acceptance tests as specified in this FQP at a reputed Third Party Lab approved by POWERGRID site.
14.2
The results of the testing of cement and reinforcement steel referred to in 13.1 and 14.1 above shall be got approved from POWERGRID site before cement and reinforcement steel are put to use. However, in exceptional cases due to exigencies of work., POWERGRID site may authorise the contractor to use Cement and Reinforcement Steel even before the test results are received. However, in all such cases, if the test results subsequently received are found to be not complying with the specified acceptance criteria, the contractor shall have to dismantle and recast all such foundations cast with such non-conforming materials at his own cost. Confirmation to this effect shall be obtained from the contractor by the Project authorities beforehand in all such cases.
ANNEXURE-I
PAGE 1 OF 1
ACCEPTING AND DEVIATION DISPOSITIONING AUTHORITIES FOR DIFFERENT CATEGORIES OF CHECKS AS ENVISAGED IN FIELD QUALITY PLAN
CATEGORY
TYPE OF CHECK
100% CHECKING/ WITNESSING BY
COUNTER CHECK/SURVEILLANCE CHECK BY
ACCEPTING AUTHORITY, IF TEST RESULTS ARE WITHIN PERMISSIBLE LIMITS
DEVIATION DISPOSITIONING AUTHORITY
A
CRITICAL
EXECUTING DEPTT. PLUS FQA REPRESENTATIVE GHQ
FQA REPRESENTATIVE AND RHQ/DHQ REPRESENTATIVE
HEAD OF DHQ
HEAD OF RHQ IN CONSULTATION WITH CQA, IF REQUIRED
B
MAJOR
EXECUTING DEPTT.
DHQ REPRESENTATIVE
HEAD OF GHQ
HEAD OF DHQ
C
MINOR
CONTRACTORS REPRESENTATIVE
EXECUTING DEPTT.
MINIMUM E4 LEVEL EXCUTIVE OF SUBSTATION/TL
HEAD OF GHQ
ANNEXURE-II PAGE 1 OF 3
ACCEPTANCE CRITERIA AND PERMISSIBLE LIMITS FOR FOUNDATION MATERIALS & CONCRETE A)
CEMENT
Description of the tests
PPC as per
Low Heat Cement
225 m2/kg
43 Grade cement as per IS : 8112 225 m2/kg
IS : 1489 300 m2/kg
225 m2/kg
160 kgf/cm2 220 kgf/cm2 30 Minutes
23 MPa 33 MPa 43 MPa 30 Minutes
16 MPa 22 MPa 33 MPa 30 Minutes
100 kgf/cm2 160 kgf/cm2 350 kgf/cm2 30 Minutes
(iv) Final Setting Time (Maximum) (v) Soundness (Le chatelier Method)
600 Minutes
600 Minutes
600 Minutes 600 Minutes
Maximum 10 mm expansion
(vi) Heat of hydration (Max.)
-
Maximum 10 Maximum mm expansion 10 mm expansion -
(i)
Fineness (min.)
(ii)
Compressive Strength (min.)
33 Grade OPC as per IS : 269
721 hours 1682 hours 6724 hours (iii) Initial Setting Time (Minimum)
(vii) Chemical Composition
As per IS
B)
COARSE AGGREGATE :
(i)
Sieve Analysis IS SIEVE DESIGNATION
(ii)
As per IS
As per IS
Maximum 10 mm expansion Max. 65 cal/gm for 7 days & max. 75 cal/gm for 28 days As per IS
PERCENTAGE PASSING FOR GRADED AGGREGATE OF NOMINAL SIZE 40 mm 20 mm
40 mm
95 to 100
100
20 mm
30 to 70
95 to 100
10 mm
10 to 35
25 to 55
4.75 mm
0 to 5
Flakiness Index
-
0 to 10 ANNEXURE-II PAGE 2 OF 3 Not to exceed 25%.
(iii)
Crushing Value
-
Not to exceed 45%.
(iv) cycle not to exceed
Soundness of aggregate -
Loss of weight after 5
applicable for concrete works
12% when tested
with Sodium sulphate and subject to froast action
18% when tested with
Deleterious material aggregate.
Not to exceed 5% of the
magnesium sulphate. (v) weight of C)
FINE AGGREGATE
(i) or Zone III.
Sieve Analysis
IS Sieve designation 10 mm 4.75 mm 2.36 mm 1.18 mm 600 Micron 300 Micron 150 Micron
(ii)
Percentage Passing for Grading Grading Zone-I Zone-II 100 100 90-100 90-100 60-95 75-100 30-70 55-90 15-34 35-59 5-20 8-30 0-10 0-10
-
Shall confirm to Zone I, Zone II
Grading Zone-III 100 90-100 85-100 75-100 60-79 12-40 0-10
Grading Zone-IV 100 90-100 95-100 90-100 80-100 15-50 0-15
For guidance of adjusting the quantity in mix of concrete, the following table may be used. Moisture Content % 2 3 4 5
Bulking % by volume 15 20 25 30
(iii)
Silt content Test : Shall not exceed 8%.
(iv)
Deleterious Materials : Total deleterious material shall not be more than 5% by weight.
(D) Standards.
REINFORCEMENT STEEL : As per relevant Indian
ANNEXURE-II PAGE 3 OF 3 (E)
CONCRETE CUBE TEST
For nominal (volumetric) concrete mixes, compressive strength for 1:1½:3 (cement : sand : Coarse aggregate) concrete shall be 265 kg/cm2 for 28 days and for 1:2:4 nominal mix, it shall be 210kg/cm2. (F)
ACCEPTANCE CRITERIA BASED ON 28 DAYS COMPRESSIVE STRENGTH FOR NOMINAL MIX CONCRETE a)
The average of the strength of three specimen be accepted as the compressive strength of the concrete, provided the strength of any individual cube shall neither be less than 70% nor higher than 130% of the specified strength.
b)
If the actual average strength of accepted sample exceeds specified strength by more than 30%, the Engineer-in-charge, if he so desires, may further investigate the matter. However, if the strength of any individual cube exceeds more than 30% of specified strength, it will be restricted to 30% only for computation of strength.
c)
If the actual average strength of accepted sample is equal to or higher than specified strength upto 30%, then strength of the concrete shall be considered in order and the concrete shall be accepted at full rates.
d)
If the actual average strength of accepted sample is less than specified strength but not less than 70% of the specified strength, the concrete may be accepted at reduced rate at the discretion of Engineer-in-Charge.
e)
If the actual average strength of accepted sample is less than 70% of specified strength, the Engineer-in-Charge shall reject the defective portion of work represented by sample and nothing shall be paid for the rejected work. Remedial measures necessary to retain the structure shall be taken at the risk and cost of contractor. If, however, the Engineer-in-Charge so desires, he may order additional tests to be carried out to ascertain if the structure can be retained. All the charges in connection with these additional tests shall be borne by the Contractor.
(G)
ACCEPTANCE CRITERIA FOR DESIGN MIX CONCRETE SHALL BE AS PER IS:456
CHAPTER-9 Guidelines
___________________________________________________________________________ CHAPTER NINE ___________________________________________________________________________ GUIDELINES Back to contents page 9.0
Pit Marking Back to contents page
Name of the Line :-
Location No. :-
Name of Contractor:-
Type of Tower :-
(i)
It should be ensured that approved drawings are available for execution of the work.
(ii)
It shall be checked that reference level has been measured correctly and recorded.
(iii)
Alignment of location shall be checked with respect to previous and next location.
(iv)
Location of centre peg / position of various land marks shall be matched as per profile.
(v)
The possibility of realignment / shifting of location shall be checked due to any new feature on the ground with respect to profile.
(vi)
The proceeding span as well as succeeding span shall be measured and compared as per the profile.
(vii)
The actual angle of deviation and bisection of the angle tower shall be measured and compared as per profile.
(viii)
The position of cross pegs in tranverse direction shall be checked.
(ix)
The safety of all the four pits should checked.
(x)
Dimensions of pits should be checked as per the drgs.
(xi)
The requirement of Benching / Revetment shall be examined and contour maps / Revetment drgs. shall prepared wherever necessary.
(xii)
In case of benching, the volume of cutting and filling shall be calculated and recorded in cu.m. as per the benching drg.
(xiii)
In case of Revetment, the volume of Revetment quantity shall be calculated and recorded as per the Revetment drg.
9.1 Stub Setting Name of the Line :-
Location No. :-
Name of Contractor:-
Type of Tower :-
(i) It should be ensured that the drgs. are approved for the stub setting. (ii) a) The depths of all four pits (A, B, C, D) shall be measured and tabulated from Ground level as well as Reference level. b) Pit dimensions shall be checked as per approved found, classifn. drg. c) Excavated soil should be stacked at least 2m away from pit edge to avoid collapse of the foundation pit. d) Undercutting of foundation shall be checked as per the drg. in case of fissured rocks. (iii) a) Tangent Tower The alignment of the template in the direction of the line shall be checked in case of tangent Tower. b) Angle Tower (b.a)
The Angle of deviation shall be checked as per the drg.
(b.b)
The alignment of template on bisection shall be checked.
(iv)
Diagonals of template shall be measured with respect to the approved drgs.
Stub Setting on Bisection (v)
The Level of template should be checked by dumpy level.
(vi)
Ht. of template above ground level shall be checked.
(vii)
The clearance (not less than 15 cm or as specified in the drg.) between lowest part of all the four stubs and base of the pit shall be checked.
(viii)
Positioning of the template support shall be checked with regard to any danger to the collapse of pit.
(ix)
Tightening and erection of the template should be checked as per drg.
(x)
Checking of stubs.
(a)
The dimensions of the stubs shall be checked as per type of tower.
(b)
The proper erection of the plates / cleats with regd. nos of properly tightened bolts shall be checked as per the drg.
9.2
Construction Materials Back to contents page
Name of the Line :-
Location No. :-
Name of Contractor:-
Type of Tower :-
i) The availability of required quantity of approved quality sand should be checked as per the approved drgs. and specifications. ii) The availability of required quantity & approved quality of both 20nmi and 40mm metal should be checked as per the approved drgs. and specifications. iii) The dimensions of the measuring box (30cm x 30cm x 39cm height) shall be checked. iv) The proportions of nominal mix should be checked as per the table given below: Grade of
Qty. of Coarse
Qty. of fine
Qty. of
Qty. of Water
concrete
Aggregate
Aggregate
Cement
M-100
6 Boxes
3 Boxes
1 Bag
1 Box less 1 Litre
M-150
4 Boxes
2 Boxes
1 bag
1 Box less 3 Litres
(v)
The required quantity and quality of water shall be checked as per specifications.
(vi)
Reinforcement steel
(a)
The diameter wise qty. & quality of the reinforcement steel shall be checked as per apprd. drgs.
(vii)
Form Boxes
(a)
The dimensions of the form boxes should be checked as per apprd. drgs.
(b)
Proper oiling of inner wall of form boxes shall be checked.
(viii)
The availability of T&P and man power shall be checked as per annexure IA & IB.
(ix)
Lean Concreting;-
(a)
The cleanliness of the pits from all foreign materials shall be checked.
(b)
Proper dewatering of the pits shall be checked.
(c)
Mix ratio of 1:3:6 concrete with 40mm metal shall be checked.
(d.a)
Concrete mixing by mixer as per specn. shall be checked.
(d.b)
Mixure running Time (Mixing Time-2 Min. ) shall be checked.
(e)
De-watering of the pit shall be checked.
(f)
The specified area and level of lean concrete in all the four pits shall be checked.
(g)
The actual consumption of the cement bag as per approved drawing shall be checked.
(x.a)
Filling of excess excavation by the lean concrete shall be checked.
(x.b)
The volume of excess lean concrete shall be measured and recorded.
9.3
Installation of Reinforcement Steel & Form Boxes Back to contents page
Name of the Line :-
Location No. :-
Name of Contractor:-
Type of Tower :-
i)
It should be ensured that the approved drgs. are available for the execution of the work.
(ii)
Reinforcement Steel
(a)
The quality and quantity of the reinforcement steel shall be checked as per the drawing and specification.
(b)
Bending / Placing shall be checked as per apprd. drgs. and specification.
(c)
The diameter (Min. Dia. - 12mm) and spacings (Max. Spacing - 500mm) of the chairs shall be checked.
(d)
The binding of the Reinforcement steel shall be checked.
(e)
Any undue development of stress due to improper bending of steel bars shall be checked.
(f)
Cleanliness of the Reinforcement steel from any foreign materials or loose rust shall be checked.
(g)
Position of bars w.r.t. stub shall be checked as per drg.
(iii)
Form Boxes :
(a)
The dimensions shall be checked as per appd. drgs.
(b)
Placing of the stub shall checked as per apprd. drg.
(c)
Water tightness of Bolts and Nuts shall be checked.
(iv)
Clear cover of 50 mm (or as per drg. / specn.) shall be checked.
(v)
Fixing of the Earth strip shall be checked as per apprd. drg.
9.4
Mixing, Placing and Compacting of Concrete Back to contents page
Name of the Line :-
Location No. :-
Name of Contractor:-
Type of Tower :-
(i)
It should be ensured that the approved drgs. are available for the execution of the work.
(ii)
Mix Ratio
(a)
Mix ratio of 1:2:4 Concrete for Pyramid / base with 20mm metal shall be checked.
(b)
Mix ratio of 1:2:4 Concrete for chimney with 20mm metal shall be checked.
(c)
Water to cement ratio shall be checked as per specification.
(iii)
Mixing done by
(a)
Running Time of mixer (Running time - 2 Min.) shall be checked.
(b)
Hand mixing (with 10 extra cement or as specified in LOA) of concrete shall be checked.
(c)
It should be ensured that the hand mixing of concrete is done on GI sheet platform to avoid mixing of concrete with undersirable material.
(iv)
The proper compaction of concrete with the help of Vibrator should be ensured.
(v)
In case of non availability of vibrator, compaction to be done by peeking rod.
(vi)
The levels and diagonals of the template shall be checked at regular intervals.
(vii)
The casting of legs in continuity shall be checked.
(viii)
Actual consumption of the cement bags shall be checked as per the drg. and specification.
(ix)
Construction of the coping shall be checked as per the appd. drg.
(x) It should be ensured that the cubes have been collected and recorded as per the table given below:
Twr. Leg.
Pyramid (Date)
Chimney (Date)
No. of cubes
A
B
C
D
(xi)
The curing of the foundation should be started after 24 hrs of construction and the foundation should be kept continiously in wet conditions by putting wet gunny bags.
(xii)
The removal of form boxes after 24 hrs of casting shall be checked.
(xiii)
Availability of sufficient qty. of water near the loc. for the backfilling shall be checked.
(xiv)
The soil for the backfilling of the foundation should be free from all foreign materials and acceptable.
(xv)
Proper compaction of the backfilling with adequate sprinkling of water shall be checked.
(xvi)
The level of backfilling upto 75 mm above ground level or as specified in specn. Shall be checked.
(xvii)
It should be ensured that the height of earth embankment of 50mm (or as per specn.) has been made along the side of back filled earth.
(xviii)
Proper curing of the chimney by wet gunny bags shall be checked.
(xix)
Careful removal of template after complete back filling shall be checked.
(xx)
Curing period of foundation and chimney checked as per specn. (Minimum period of curing 14 days after concreting both in Morning & Evening).
(a) The date of start of curing and date of completion of curing shall be recorded. (xxi)
The arrangement for testing of the cubes as per approved FQP shall be checked.
(xxii)
The removal of all the surplus materials from site shall be ensured.
Note :
Foundn. Is cleared for tower erection subject to fulfillment of part (I) before tower erection and part (II) in due course as per planning.
Part-II (ii)
(i)
Revetment Benching proposal status
Rivetment / Benching likely execution date
___________________________________________________________________________ CHAPTER-10 CHAPTER TEN
Check Format
___________________________________________________________________________ CHECK FORMAT Back to contents page 1.0
Check format for Pit Marking Back to contents page
Name of the Line :-
Location No. :-
Name of Contractor:-
Type of Tower :-
(i)
Apprd. Drg. nos.
……………………………………
(ii)
Reference level
……………………………………
(iii)
Alignment of loc. W.r.t. previous and next. O.K./NOT O.K.
App
Loc. (iv)
Loc. Of center peg/position of various land O.K./NOT O.K. marks are matching as per profile
(v)
Any new features on grnd. W.r.t. profile Yes/No necessitating realignment/shifting of loc. Or due to any other reasons
(vi)
Span on both sides of loc.
A Per profile
Actual
(Mtrs.
(Mtrs.)
a)
Preceding span (loc. No.
)
b)
Succeeding span (loc. No.
(vii)
Angle of deviation and bisection in case of As per profile
)
angle tower loc. a)
Angle of deviation
O.K./NOT O.K.
Actual
b)
Bisection found
O.K./NOT O.K.
(viii)
Position of cross pegs in transverse dirn.
O.K./NOT O.K.
(ix)
Position of all four pits are on leveled grnd. Yes/No And safe
(x)
Dimensions of pits are as per drgs.
O.K./NOT O.K.
(xi)
Whether Benching/Revetment reqd. if yes, Yes/No then
a)
If countour maps/revetment drgs. prepared
Yes/No
b)
Possibly calculate vol.
……….. cu.m. FOR POWERGRID Signature ……………………….. Name …………………………… (Jr. Engr./E1/E2/E3) Date ………………………..
2.0
Check format for Foundation Classification Back to contents page
NAME OF LINE : -
LOCATION NO. :-
NAME OF CONTRACTOR :-
TYPE OF TOWER :
(i)
Strata wise pit details STRATA DEPTH
RECEIVING END
STRATA DEPTH ………………… ………………… …………………. ………………… PIT C
PIT B STRATA DEPTH
STRATA DEPTH Trial pit details/ Bore log details
PIT D
SENDING
END
PIT A NOTE : CLASSIFICATION MAY ALSO BE GIVEN ON TRIAL PIT OR ONE PIT EXCAVATION BASIS. (a)
Predominant soil.
(ii)
Sub soil water table details as on date. PIT A
(iii)
PIT B
PIT C
PIT D
Water table in nearby well as on date
…………
…… mtrs. (iv)
Maxm. Subsoil water table in monsoon season after thorough local enquiry
…………
…… mtrs. (v)
Surface water table on grnd. In monsoon season and its duration.
…… mtrs. For
….. days (vi)
Type of cultivation Paddy fields/Cultivated land/Barren land
(vii)
Whether encasement of stubs reqd. due to surface water?
Yes/No
If yes, ht. Of encasement above grnd. Level
…
…………. Mtrs. (viii)
Whether soil invest. Carried out at this loc. or nearby loc.
Loc. No. ………
…… (ix)
If this loc. strata details are comparable with above soil invest. Report or any other loc. of this line.
Loc. No. ……………… (x)
Details of Soil Invest. Report
……… (a)
STRATA DEPTH
Loc. No. ………
……………. ……………. …………….. ……………..
(b)
Subsoil water table
…………. Mtrs.
(c)
Ultimate bearing capacity
……… Kg./m2
(d)
Angle of repose. ()
……….. degrees
(xi)
Fndn. Classifn. Proposed by contractor
(xii)
Fndn. Classifn. Recommended As per soil
Actual Invest.
Remarks/Reasons :………………………………………………………………………………………………… ………………………………………………………………………………………………… FOR POWERGRID Signature ………………..……… Name …… ……………………... (E1/E2/E3) Date …… ………………………. Approval Site visited on ………………… and details verified. The classifn. of fndn. Is approved as ………………… FOR POWERGRID
Signature ………………..……… Name …… ……………………... (Line Inch./Grp. Head) Date …… ……………………….
3.0
Check format for Stub Setting Back to contents page
Name of the Line :-
Location No. :-
Name of Contractor:-
Type of Tower :-
(i)
Apprd. Drg. nos.
……………………………………
(ii)
Pit Dimensions
……………………………………
(a)
Depth of pits
App From Ref. level
Ground level
Pit A Pit B Pit C Pit D (b)
Pit dimensions are as per apprd. Foundn. Classifn.
Yes/No
(c)
Excavated soil is kept 2m away from pit edge
Yes/No
(d)
Under cutting done in case of fissured rocks
Yes/No
(iii)
Alignment of template
(a)
Tangent Tower
(a.a)
In the direction of line
(b)
Angle Tower
(b.a)
Angle of deviation
(iv)
Diagonals of template
Yes/No …………. Degrees
AC ……………….. m BD ……………. M = Angle of Deviation. PQ = Line of Bisection. (Lines AD and BC are perpendicular to PQ) Stub setting on bisection.
(v)
Level of template checked by dumpy level
…………… YES/NO
(vi)
Ht. Of template above grnd. Level
O.K./Not O.K.
(vii)
Clearance between lowest part of stub and
App
base of pit (Not less than 15 cm or as specified in the drg.) Leg A ………………. Cm Leg B ……………… Cm Leg C ……………… Cm Leg D …………….. Cm (viii)
Template support positioning is causing any O.K./NOT O.K. danger to collapse of pit
(ix)
All members of template are fixed as per drg. YES/NO and fully tightened
(a)
Stub dimensions are as per type of tower
YES/NO
(b)
All plates/cleats fixed with reqd. no. of YES/NO Nut/Bolts and are fully tightened
CERTIFICATE : - Stub Setting Approved. FOR POWERGRID Signature ………………..……… Name …… ……………………... (Line Inch./Grp. Head)
Date …… ……………………….
4.0
Check format for Construction Materials Back to contents page
Name of the Line :-
Location No. :-
Name of Contractor:-
Type of Tower :-
(i)
Quality/Qty. of sand as per apprd. Drgs. and specns. Qty. Reqd.
Qty. Avail.
Apprd. Source
Quality (OK/NOT OK)
(ii)
Quality/Qty. of metal as per apprd. Drgs. and specns. Size
Qty. Reqd.
Qty. Avail.
Apprd. Source
Quality (OK/NOT OK)
20 mm 40 mm
(iii)
Dimensions of the measuring Box (30 cm x 30 cm x 39 cm Height)
(iv)
OK/NOT OK
Proportions of nominal Mix. Grade of
Qty. of Coarse
Qty. of fine
Concrete
Aggregate
Aggregate
M-100
6 Boxes
3 Boxes
Qty. of Cement
Qty. of Water
1 Bag
1 Box less 1 Litre
M-150
4 Boxes
2 Boxes
1 Bag
1 Box less 3 Litres
(v)
Quality & Qty. of water as per specns.
O.K./NOT
O.K. (v)
Reinforcement steel
(a)
Qty. & Qualify as per apprd. Drgs./specns. Dia
Qty. Reqd. (MT)
Qty. Avail. (MT)
Apprd. Source
Quality (OK/NOT OK)
6 mm 8 mm 12 mm 16 mm 32 mm .. mm .. mm
(vii)
Form Boxes
(a)
Dimensions are as per apprd. Drgs.
O.K./NOT
O.K. (b)
Oiling of inner wall of form boxes O.K./NOT O.K.
(viii)
T&P and man power as per Annexure IA & IB are available at site
YES/NO
CERTIFICATE : Material & T&P Cleared for lean concreting. (ix)
Lean Concreting
(a)
Pits are free from all Foreign Materials
(b)
Pits are free from standing water
YES/NO
(Dewatering continued in advance by Pumps/Buckets)
YES/NO
(c)
Mix ratio 1:3:6 with 40 mm metal YES/NO
(d)
Concrete mixing by mixer as per specn.
(e)
Mixture running Time (Mixing Time-2 Min.)
YES/NO
OK/NOT OK (f)
De-watering done
YES/NO/NOT
REQUIRED (g)
Lean concreting done upto specified level and area in all the four pits
(h) PER DESIGN
YES/NO
No. of cement bags consumed
AS
ACTUAL
(x)
In case of excess excavation filling is done by lean concrete & no loose soil is permitted for filling. Vol. Of excess lean concrete ……………. Cu.m.
CERTIFICATE : Pits are cleared for installation of reinforcement and form boxes. FOR POWERGRID Signature ………………..……… Name …… ……………………... (E1/E2/E3) Date …… ……………………….
5.0
Check format for Installation
of Reinforcement Steel & Form Boxes Back to contents page Name of the Line :-
Location No. :-
Name of Contractor:-
Type of Tower :-
(i)
Apprd. Drg. Nos.
…………
…………….. (ii)
Reinforcement Steel …………
…………… (a)
Quality/Qty./as per specn.
YES/NO (b)
Bending/Placing as per apprd.
Drgs.
YES/NO
(c)
Reqd. no. of chairs provided (Min. Dia-12 mm, Max. Spacing-
500 mm)
YES/NO
(d)
Binding done as per specns.
YES/NO (e)
Any undue stress or bending of
steel bars
YES/NO
(f)
Steel is clean and free from loose
rust or any other foreign matls. YES/NO (g)
Position of bars w.r.t. stub as per
drg.
OK/NOT OK
(iii)
Form Boxes :-
(a)
Dimensions as per appd. Drgs. OK/NOT OK
(b)
Placing w.r.t. stub as per apprd.
Drg.
OK/NOT OK
(c)
Bolts and Nuts are watertight
YES/NO
(iv)
Clear cover of 50mm (or as per
specn.) available
YES/NO
(v)
Earth strips fixed as per apprd.
Drg.
YES/NO
CERTIFICATE : Cleared for foundation casting. FOR POWERGRID Signature ………………..……… Name …… ……………………... (E1/E2/E3) Date …… ……………………….
6.0
Check format for Mixing,
Placing and Compacting of Concrete Back to contents page Name of the Line :-
Location No. :-
Name of Contractor:-
Type of Tower :-
(i)
Apprd. Drg. Nos.
…………
Mix Ratio
…………
…………….. (ii) …………… (a)
For Pyramid/base with 20 mm
metal with ratio 1:2:4 (b)
YES/NO
For chimney with 20 mm metal with ratio 1:2:4
YES/NO
(c)
Water to cement ratio as per
specification
YES/NO
(iii)
Mixing done by
(a) (b)
Mixer (Running time – 2 min.) Hand mixing (with 10% extra
cement or as specified in LOA) YES/NO (c)
Hand mixing done on GI Sheet
platform
YES/NO
(iv)
Use of poking rod for compacting YES/NO
(v)
Use of vibrator for compacting YES/NO
(vi)
Checking of template levels & its diagonals at regular intervals. OK/NOT OK
(vii)
Casting of legs done in continuity YES/NO
(viii)
No. of cement bags consumed AS PER DRG.
(ix)
ACTUAL
Coping is done as per appd. Drg. YES/NO
(x)
Details of cubes collection. Twr. Leg
Pyramid (Date)
Chimney (Date)
No. of cubes
A B C D (xi)
Curing is started after
24 hrs. of foundn. Casting and foundn. Kept continuously in wet condn. By putting wet gunny bags or otherwise.
YES / NO
(xii)
Form Boxes are
removed after 24 hrs. of casting
YES/NO
(xiii)
Sufficient qty. of
water available at loc. Before backfilling YES/NO (xiv)
Back filling is done by
soil as per specn. and free from foreign material.
YES/NO
(xv)
Backfilling is done in
layers with proper compacting and adequate water sprinkling
YES/NO
(xvi)
Backfilling is done
upto 75 mm above ground
level or as specified in specn.
YES/NO
(xvii)
Earth embankment of
ht. 50 mm or as per specn. made along the side of backfilled earth
YES/NO
(xviii)
Sufficient qty. of
water sprinkled over backfilled earth and chimney kept wet by gunny bags.
YES/NO
(xix)
Template is removed
after complete back filling
YES/NO
(xx)
Curing of backfilled
earth & chimney carried out for period as per specn. (Minimum period of curing 14 days after concreting both in Morning & Evening) YES/NO (a)
Date of start of curing ………………….
(b)
Date of completion of
curing
…………………
(xxi)
Cubes sent for Testing
as per approved FQP
YES/NO
(xxii)
All the surplus
materials removed from site
YES/NO
CERTIFICATE : Foundn. Is cleared for tower erection subject to fulfillment of part (I) before tower erection and part (II) in due course as per planning. Part-I Setting period (28 days) is allowed as per specn. Part-II (i)
Revetment Benching proposal status
…………………….
(ii)
Revetment/Benching likely execution date
……………………… FOR
POWERGRID Signature ………………..……… Name …… ……………………... (E1/E2/E3) Date …… ……………………….
ANNEXURE-IA Back to contents page TOOLS & PLANTS FOR Excavation, Stub Setting and Concreting A.
Tools & Plants reqd. : Tools & Plants reqd. for excavation, stub setting and concreting gang shall be as follows :
(1)
Stub setting templates
-
2 Nos./as per reqt.
(2)
Stub setting jacks
-
Min. 20 Nos./as per reqt.
(3)
Form Boxes/chimneys
-
Min. 4 Nos./as per reqt.
(4)
Mixer machine Diesel Engine driven
-
2 Nos.
Hand driven
-
1 No.
(5)
Needle vibrator for compacting
-
2 Nos.
(6)
De-watering pumps
-
2 Nos.
(7)
Air compressor for drilling holes in rock
-
As per reqt.
(8)
High carbon drilling rods. For drilling holes in rock
-
As per reqt.
(9)
Exploder
-
As per reqt.
(10)
Water tanker trailer
-
2 Nos.
(11)
Theodolite with stand
-
1 No.
(12)
Ranging rods with flag
-
12 Nos.
(13)
Dumpy level with stand
-
1 No.
(14)
Levelling staff
-
1 No.
(15)
Survey Umbrella
-
1 No.
(16)
Concrete cube moulds
-
6 Nos.
(17)
Wooden shuttering & Poles
-
As per reqt.
(18)
Mixing sheets
-
12 Nos.
(19)
Measuring boxes
-
6 Nos.
(20)
Sand screen 4.75 mm
-
2 Nos.
(21)
Empty Barrel (200 L capacity)
-
6 Nos.
(22)
Ladder, 3.5 meter length
-
5 Nos.
(23)
Steel Tape (30 mts.)
-
2 Nos.
(24)
Engineer’s spirit level
-
2 Nos.
(25)
Steel Piano wire/Thread
-
50 m
(26)
Crow Bar
-
12 nos.
(27)
Pick Axe
-
12 Nos.
(28)
Spade
-
15 Nos.
(29)
Shovels
-
8 Nos.
(30)
Cane Basket
-
20 Nos.
(31)
Sledge Iron Hammer (0.9 kg)
-
4 Nos.
Iron Hammer (4.5 kg)
-
4 Nos.
12 mm dia
-
30 m
38 mm dia
-
150 m
3.5 m long
-
2 Nos.
1.5 m long
-
2 Nos.
(34)
Blasting mats.
-
As per reqt.
(35)
Tommy Bars, plumb BOB (0.45 kg) Spanners (Both ring & flat)
-
As per reqt.
(36)
Buckets
-
12 Nos.
(37)
Tents, water drums, camping, cots, tables, -
As per reqt.
(32) (33)
Manila Rope
Pocking rod (16 mm dia)
chairs & petromax etc. B.
Transport reqt. for stub setting/concreting gang
1.
Truck
-
1 No.
2.
Tractor with trailer
-
1 No.
3.
Motor cycle
-
2 Nos.
4.
Jeep
-
1 No.
C.
Safety Equipments
1.
Safety helmets
-
16 Nos.
2.
First Aid Box
-
1 No.
3.
Hand gloves
-
16 Pairs
4.
Shoes
-
16 Pairs
5.
Welding goggles
-
4 Sets
ANNEXURE-IB Back to contents page MANPOWER REQUIREMENT FOR EXCAVATION, STUBSETTING & CONCRETING GANG (1)
Engineer (Part time)
1 No.
(2)
Jr. Engineer
4 Nos.
(3)
Skilled Manpower :
(a)
Fitter
8 Nos.
(b)
Mixer m/c operator
2 nos.
(c)
Water pump/vibrator operator
2 Nos.
(d)
Carpenter As
per
reqt. (e)
Skilled workers for
miscellaneous works
8 Nos.
(4)
Unskilled
workers
40 Nos. (5)
Mechanic As
per
reqt. Note :
Manpower strength to
be increased from 65 to 85 depending upon Soil parameters and other site conditions. Also for specified jobs like benching/Revetment, blasting etc., separate manpower is to be engaged.
ANNEXURE-IC Back to contents page REINFORCED CONCRETE RETAINING WALLS 1.0
Cantilever Retaining Walls : A cantilever retaining wall consists of a vertical cantilevering slab called the stem and a base slab (fig. 40). This type of wall may be used to retain earth up to 6 meters. For greater heights a counterfort retaining wall should be used. The base slab consists of : (i)
The toe slab and (ii)
Heel slab. The heel slab is that part of the base slab, under the retained earth. The toe slab is the projection of the base slab on the front side of the retaining wall. Top width of stem
=
20 cms.
Bottom width of stem
=
To be computed
Width of base slab
=
B
=
0.5 H to 0.6 H
b
for walls without surcharge b
=
Toe projection
= H
=
0.7 H for surcharged walls H b _______ or ____ 6 3 Overall height of wall.
The bottom width of the stem should be determined from bending moment considerations. Usually the thickness of the base slab is made equal to the bottom thickness of the stem. Method of design. (a) A tentative cross-section should be first assumed.
(b)
For one metre run of the wall the maximum bending moment at the bottom
of the stem is determined. By equating the bending moment to the moment of resistance of Qbo the effective depth is determined. The cover the reinforcement in the stem is usually 3 to 4 cm. Hence assuming the diameter of the reinforcement the overall width of the stem at the bottom is determined. The base slab thickness is made equal to the width of the stem at the bottom. (c)
The stability of the structure is studied. The maximum and minimum
pressures at the base are worked out. The maximum pressure at the base shall not exceed the safe bearing capacity of the soil.
(d)
The reinforcement required for the stem is computed. This is given by
Max. B.M. in Newton cm. At (sq. cm) = _____________________
or
Max. B.M. in kg. cm. ____________________
14000 x 0.87 d (e)
1400 x 0.87 d
Calculate the maximum bending moment for the toe slab. The toe slab is designed as a cantilever and acted upon by upward soil reaction. The depth provided is checked for the bending moment. A cover of 5 cm. To 6 cm. may be provided to reinforcement in the base slab.
(f)
Calculate the maximum bending moment for the heel slab. The heel slab is also designed as a cantilever subjected to downward loads consisting of its own weight, the weight of the soil above it and super load and any loading due to the surcharge, and upward soil reactions. The reinforcement required is now determined.
(g)
The tendency for the wall to slide forward due to the lateral earth pressure should be investigated. A factor of safety of at least 1.5 shall be provided against sliding. If the factor of safety is insufficient a key (also called rib or cut off wall) would be designed to prevent the lateral movement of the structure. (See Fig. 43). Figs. 41 and 42 show how the various components of a cantilevering wall can fail.
The above figures must obviously give an idea as to where the reinforcements are required. Fro the stem, reinforcement is required near the earth side. For the toe slab the reinforcement is required at the bottom of the slab. For the heel slab the reinforcement is required at the top of the slab. For the key the reinforcement is required on that side where convexity of bending will occur (see Figs. 42 and 43). Fig. 43 shows a section of an R.C. retaining wall showing places where the main reinforcements are required.
Usually the requirement of reinforcement for the key will be small and hence alternate bars of toe slab may be continued and bent down to form the reinforcement for the key. The key may alternatively be provided under the stem so that alternate bars of the stem reinforcement may serve as reinforcement for the key. Shear reinforcement. Shear reinforcement is not normally used in retaining walls. The resistance of the concrete itself must be sufficient to resist the sharing forces imposed. Distribution steel. Horizontal distribution steel should be provided in both the stem and the base slab. This reinforcement shall not be less than 0.15% of the gross area of concrete. Expansion and contraction joints. Keyed expansion and contraction joints should be provided at 30 m intervals.
2.0 Counterfort Retaining Walls Retaining walls over 5.5 metres in height are usually made of the counterfort type. The various components of such a wall are shown in Fig. 44. (i)
Upright slab. The upright slab will be designed as a continuous slab
spanning on the counterforts and subjected to lateral earth pressure. Let the lateral, horizontal pressure intensity at the bottom of the upright slab be p per sq. metre. Consider the bottom 1 metre deep strip of the upright slab. If the spacing of counterforts be 1 metres centre to centre then the maximum being moment for theupright slab = pI2/12. The thickness required to suit this bending moment may now be computed. The slab is usually built of the same thickness. The main reinforcement requirement may now be calculated. This steel runs horizontally, its requirement being away from the earth side at sections mid-way between the counterforts and near the earth side at the sections on the counterforts. The slab shall also be provided with distribution steel at not less than 0.15% of the gross area of the section. The distribution steel is placed vertically near both the faces, since the upright slab is considerably thick. These bars should form a mesh with the horizontal bars. Hence these bars will have to be supported by additional horizontal bars at certain places where main horizontal bars are not forming a mesh with them. (ii)
The base slab. The width of the base slab may be made 0.6 H to
0.7 H where H is the overall height of the retaining wall. The base slab consists of the toe slab and the heel slab. The toe projection is usually onefourth of the total width of the base slab.
Heel slab. The heel slab should be designed as a continuous horizontal slab with the counterforts as the supports. The slab is designed as a continuous slab consisting of continuous strips parallel to the wall. Each stip is uniformly loaded; but the loading on the various strips varies from a maximum at the heel edge to a minimum near the wall. The loading on a strip of heel slab will consist of the following : (a)
Dead load of the strip
(b)
Weight of earth above the strip
(c)
Vertical component of lateral pressure in the case of earth
surcharged at an angle. If the surcharge angle is a, then the intensity of vertical component of lateral pressure =
Cp wh’ sin tan
Cos – (cos2 – cos2)1/2 Where Cp = cos _______________________ Cos + (cos2 – cos2)1/2
h’ = height of earth above the strip = angle of repose.
(d)
Superload intensity acting on the retained soil if any
(e)
Upward soil pressure.
It will be seen that the net load on the heel slab will be a downward load. If the net load be Q per unit area near the heel end, then consider a one metre wide strip near the heel end. The maximum bending moment for the strip = QI2/12. The moment will be a sagging moment at sections midway between the counterforts and will be a hogging moment at the sections over the supports. Thickness of the base slab. The author suggests that this may be taken not less than the following, in order it may not be found unsafe from B.M. and S.F. considerations. D = 4.17I (H)1/2 D = 2 IH Where D = Thickness of the base slab in cm. I = Spacing of counterforts in metres. H= overall height of wall in metres. If the soil is surcharged at angle increase H by 0.7m.
If the soil is superloaded ------------------------------------------------
Super load intensity increase H
by
Wt. Per unit volume of the soil
Spacing of counterforts. Counterforts are spaced from 3 metres to 3.50 metres. This spacing may also be taken from one third the height of the wall to half the height of the wall. The spacing may also be computed as the spacing for which the maximum bending moment for the upright slab requires an overall thickness of 30 cm. Let the spacing be 1 metres. Let the height of upright slab be h metre. In M.K.S. units, to satisfy the above condition,
454.8 l = ---------- metr for M 150 concrete (wh)1/2 In S.I. units, t=
1438.25.8 --------------(wh)1/2
metr for M 150 concrete
Toe slab. The design of the toe slab depends upon whether the toe slab is allowed to remain a cantilever, or it is made to act as a continuous slab by providing front counterforts. When the front counterforts are not provided the toe slab should be designed as a cantilever slab subjected to upward soil reaction. But if a front counterfort be provided then, the toe slab shall be designed as a continuous slab with the front counterforts as the supports. In such a case at section midway between the front counterforts the bending moment for the toe slab will be of a hogging type, while at the section on the supports, the bending moment for the toe slab will be of the sagging type. (iii)
Counterforts. As mentioned already the retaining wall may have main
counterforts or main counterforts and front counterforts. Main counterforts. These are designed as vertical cantilevers held in position by the base slab. The loading on these counterforts is due to the lateral earth pressure acting on the upright slab. Let h be the height of cantilever above the base. L = spacing of counterforts =surcharge angle Total horizontal force transferred to one counterfort wh2 Ph = Cp --------- I cos acting at a height of 2
h/3 above the base Max. bending moment for the counterfort = M = Ph (h/3) M = Cp (wh3)/6 I cos The reinforcement required to resist this bending moment can be easily calculated. At = (M/at) sec
Where = inclination of the reinforment with the normal to the horizontal section of counterfort (i.e., inclination of the reinforcement with the vertical). We know At (M/a) (M/d) (M/h) approximately At (h3/h) At h2 If At1 and At2 are the areas of steel required at depths h1 and h2 We have At1/At2 = h12/h22 But At is proportional to the number of bars. Let n be the number of bars at the depth h n1 be the number of bars at the depth h1 n2 be the number of bars at the depth h2 n3 be the number of bars at the depth h3 Then we have n1/n = h12/h2 …………………………………….. (1) n2/n = h22/h2 ……………………………………. (2) n3/n = h32/h2 …………………………………… (3) and so on. Hence at what depth a certain number of bars can be curtailed, can be determined. Front counterforts. These are designed as horizontal cantilevers. The loading on these will be due to the upward soil reaction on the toe slab. It is quite likely that the front counterfort will be subjected to considerable shear force. Hence shear stirrups of two or four legs must also be provided. The main reinforcement of the main counterfort and also that of the front counterfort should be embedded into the base slab for sufficient length to
develop the necessary bond strength. The bars of the main counterfort should be securely anchored at the bottom by bending them back into the base slab. In the case of a wall provided with main as front counterforts the critical section for the max. bending moment for the main counterforts shall be taken at a level corresponding to the top level of the front counterfort. Horizontal ties connecting the main counterforts and upright slab. Horizontal links of two legs are provided connecting the main counterfort and the upright slab to tie the wall to the counterfort and also to resist diagonal tension in the counterfort. These links must be looped around the main reinforcement of the counterfort. Fig. 47 shows the horizontal links and Figs. 48 and 49 show two alternative ways in which the horizontal links may be provided.
Vertical ties connecting the counterforts and the Heel slab. We know that the heel slab will transfer its load to the counterforts which are supporting them. In order that the heel slab may transfer its load to the counterfort, it is necessary to provide vertical ties which are in the form of vertical links of two legs.
---------------------------------------------------------------------------------------------------------------BIBLIOGRAPHY ---------------------------------------------------------------------------------------------------------------(1)
“Transmission Line Structure” by S.S. Murthy and A.R. Santhakumar.
(2)
“Manual on Transmission Line Towers” – CBI&P – Technical Report No. 9.
(3)
“Workshop on Transmission Line” – CBI&P-Vadodara (29th Nov. –2nd Dec. 94).
(4)
“Symposium on Design & Protection of 400 KV Transmission Lines” – CBI&P – Publication No. 131.
(5)
“Code of Practice for Design and Construction of Pile Foundation” – IS 2911 (Part-I to Part-IV).
(6)
“Pile Design and Construction Practice” – M.J. Tomlinson.
(7)
“Manual on Transmission Line Towers” – Central Board of Irrigation and Power.
(8)
“Handbook on under-reamed and Bored compaction Pile Foundation” – Central Building research institute, Roorkee.
(9)
“Construction Manual, Part-II, Transmission Line Construction” SRTS – Power Grid Corporation of India Ltd.
(10)
“Soil Mechanics and Foundation Engineering” by K.R. Arora.
(11)
“Modern Geotechnical Engineering” by Alam Singh.
(12)
“Foundation Design” by Wayne C. Teng.
(13)
“Construction Planning equipment & Methods” by Robert L. Peurifoy and William B. Ledbetter.
(14)
“Foundation analysis and Design” by Joseph E Borles.
