Method Statement

Larsen & Toubro Limited ECC Division

Panipat Elevated Highway Project National Highways Authority of India

       

TABLE OF CONTENTS

DESCRIPTION

PAGE

1. INTRODUCTION

2

2. ASSUMPTIONS

3

3. REFERENCE

4

4. SCOPE

5

5. MATERIALS

6

6. ELEVATED STRUCTURE

7

7. CONSTRUCTION METHODOLOGY

8

8. CURING

18

9. CONCLUSION

19

Method Statement for Construction of Elevated Structure

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       

1. INTRODUCTION This method statement describes in brief the broad sequence and method of construction of six lane elevated structure of length 3.6 km covering central built up Panipat Section including Gohana road crossing, Sanauli road crossing, bus stand and skylark tourist complex on BOT basis. This Method Statement shall be read in conjunction with our construction methodology drawings attached in Appendix A of this booklet.


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       

2. ASSUMPTIONS Following assumptions have been made to arriving at this methodology:  Pier

for elevated structure will be cast in single pour.

 The

safe Bearing Capacity of soil is considered as 10 t/Sqm for the

casting yard area.  The

density of reinforced cement concrete considered as 2500 kg /

cu.m.


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       

3. REFERENCES Following document has been referred for the preparation of this method statement: 1. Technical Proposal – Appendix 5


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       

4. SCOPE The scope of work includes the following major works: •

•

•

Construction of foundation [Bored cast in situ piles] Construction of Sub structure [Pier and Pier cap] Construction of Super structure [PSC I-Girder and Cast in situ slab]


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       

5. MATERIALS 5.1. Concrete: Concrete for the entire works will be supplied from captive batching plants strategically located. Alternatively concrete will be sourced from approved RMC plants. Materials used in the concrete will be tested to check their conformity to project specification / standards. Concrete will be transported from plant to the work place in transit mixtures. Admixtures will be used with the prior approval of the engineer. Temperature of the concrete will be maintained as per the specifications / standards. 5.2. Reinforcement:

All reinforcement works will be done in centralised

reinforcement yard. Reinforcement will be stacked grade wise with suitable identities. Bar bending schedules will be prepared based on approved construction drawings and submitted for engineers’ approval. All cutting and bending will be done as per approved bar bending schedules. The reinforcement steel will be cleaned before use to remove rust, oil, grease, salt and any other deleterious materials. Reinforcement cages will be prefabricated to the extent possible to reduce the fixing time at site. Required cover blocks will be provided as per specifications / standards.


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       

6. ELEVATED STRUCTURE General and Structural Arrangement: The Elevated Structure starts at a chainage Km 88+760 and ends at Km 91+819. The structure consists of continuous deck structure supported on single column piers founded on pile foundations. The total length of structure has been divided in to six segments as follows:

S.No

Segment No.

Chainage in m

Total length in

No. of Spans

m 1

Segment 1

88.560 to 89.060

500

9

2

Segment 2

89.060 to 89.550

490

17

3

Segment 3

89.060 to 90.089

539

17

4

Segment 4

90.089 to 90.570

481

15

5

Segment 5

90.570 to 90.900

330

11

6

Segment 6

90.900 to 92.240

1340

31

The deck of the structure is designed to cater for three lanes of traffic in each direction with two separate decks. The carriageways are separated by median of 1.2m in the elevated structure. The elevated structure comprises multispan deck slab on precast pretensioned girders (span varies 27m to 31m) supported on single rectangular / square type piers and abutment twin columns resting on pile foundations.


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       

7. CONSTRUCTION METHODOLOGY 7.1. Survey and Layout of Elevated structure: The survey works for approaches will start with setting out of grids and marking the existing ground features for the entire stretch of elevated structure. Pier locations and bench marks for the regular survey will be fixed, and the benchmarks will be cross-checked by closing the traverse and ascertain the accuracy of bench marks. The survey pillars will be established at convinent locations. 7.2. Soil Soil Investigation: Ground investigation if required will be carried out as per relevant codes. It is proposed to deploy rotary type of drilling rigs for drilling the bores of 150mm diameter using temporary casings. The method of advancement and diameter of the bore will be such that the boring will be completed and logged to the scheduled depth, and samples of the specified materials will be obtained, in situ testing will be carried out as required. In locations where water table is penetrated and disturbance of soil is likely, positive hydraulic head will be maintained in the bore. While the bore progresses, the sampling frequency and the type of samples will be obtained as per the requirements. While drilling in the bore hole is in progress the change in soil strata, colour of water, rate of penetration of the drilling rod, starting and completion of each run, any water loss, side collapsing etc. will be recorded and details furnished. All samples will contain the full details of the location of bore, depth at which recovered etc. The samples of soil collected from the bore hole will be packed in sealed packets and sent to soil laboratory for tests.


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        7.3. Site Infrastructure: The site infrastructure will consist of project site offices and infrastructure facilities for Precast I Girder casting, reinforcement yard and stacking. This will contain temporary offices for the project managerial personnel, stores and cement godown, work shop and generator shed etc. For layout of casting yard and site facilities refer our drawing no O5086-Q-BR-CM-GA0008. Casting Yard: The various components involved in the casting yard are listed below:  Casting

Bed for casting I-Girders.

 Moulds

for I-Girders

 Gantries

for handling PSC Girders from casting bed

 Gantries

for handling reinforcement cage and mould side shutters

 Various

rail tracks for handling & shifting the girders.

Based on the total number of girders to be casted and time duration available, it is proposed to provide two numbers of casting beds. The casting bed number: 1 will have provision for 8-girder casting and casting bed number: 2 will have provision for 4-girder casting. Based on the length of girders and Prestressing strand arrangement, the Type A girders will be cast in bed number: 1 and Type B & C will be cast in bed number: 2. The casting bed will have bulkhead provisions for stressing the strands before casting and distressing the strands once the casting is completed. Moulds for casting I-girders: - The I-girder mould will be fabricated out of structural steel plates with sufficient stiffeners to resist the concrete pressure. It is planned to deploy four bottom and two side shutters. The gantry available in the yard can handle the side shutter from one mould to another.


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        The PSC Girders will be cast in respective beds and once the casting is completed, the strands will be distressed and the girders will be shifted to stacking yard. The stacking of girders will be done in two tyres as shown in our drawing O5086-Q-BR-CM-GA-0044. The I-Girders from the stacking yard will be shifted to erection location by long bedded trailers.


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        7.4. Pile Pile Foundation All piling works for the foundation will comply with the requirement as per the specifications for piling. The pile points will be marked at specified locations, the hydraulic rotary drilling rig (or) RTC rig is aligned to the exact location and the verticality of the Kelly is checked. The temporary casing if required is driven along with the advancement of pile boring. No permanent casing is envisaged. The verticality of the temporary casing is then checked by spirit level while lowering of bore and is recorded. The process of lowering the casing and boring by auger is continued till the temporary liner reaches required level. The verticality and the lateral shift of the pile are checked at regular intervals. When the bore is intercepted with soft rock in the process of boring, the tool bit will be changed from soil auger to rock auger/barrel for further boring through soft rock. Once pile reaches the level as specified in drawing, the boring is stopped and the bore is cleaned by bucket and sounding is checked. The pre-fabricated reinforcement cages in standard lengths will be cut for the required length taking into account the bore depth, cut-off level, lap length etc. Reinforcement cages are then welded together into the bore. Cover blocks of suitable size will be tied to the reinforcement and lowered. Before lowering the reinforcement cage the lap length and welds will be checked and recorded. Once the reinforcement cage is placed in position, tremmie pipes are lowered up to the toe level and the bore is flushed properly. Content coming out of the bore is checked for rock, sand and soil particles if any. Once the bore is clear, the same will be approved by the Engineer. The concrete for pile of the required grade and slump as per mix-design will be produced at the batching plant and transported to site using transit mixers and placed by suitable method. Through tremmie pipe the concrete will be allowed to Method Statement for Construction of Elevated Structure

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        overflow to at least 1m above the cut off level. The tremmie pipes and temporary casing will be removed in stages as the concrete builds up in the pile. The tremmie will be inside concrete by minimum 1.5m at all the times till end of concrete. The pile load test will be carried out at location specified by client.


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        7.5. Pile Pile Cap Once all the piles at a pier location are completed, the reconnaissance survey with the Engineer will be done and the pile cap layout will be marked on the ground to commence the excavation work for pile caps. Open excavation of slope 1:1 with a bottom working space of 0.6 m maximum is considered. The excavation will be done using excavator up to 100 mm above the binding concrete level. The dressing will be done manually and the loose patches will be removed and compacted using a hand hammer. The sides of the excavated pits will be protected using shoring wherever required so as to prevent collapse and also to allow for the movement of traffic in the adjoining area. The pile heads will be chipped to the required level i.e. to the soffit level of the pile cap and the blinding concrete will be placed. Reinforcement from the pile will be bent to the required shape and the pile cap reinforcement will be placed and tied along with starter bars for the pier. The side forms / block work with solid blocks for the pile cap will be fixed and checked for the edge co-ordinates and levels. After approval of the engineer, concrete will be placed in position. In the mean time the starter concrete for the pier will be cast on the top of the pile cap, which will be used for casting the piers. The pile cap will be cured for 14 days. Back filling of the pile cap will be done in layers and compacted using excavated materials/ fill material as required in specification.


Page 13 of 19



        7.6. Pier Fixing of Reinforcement : After casting the pile cap & starter for the pier, the reinforcement for the pier shall be placed & tied. All reinforcement will confirm to the requirement of the specifications and as shown in the approved drawings / bar bending schedule. The prefabricated renforcement

cage

will

be

kept

in

position with the help of crane. The cage will be aligned and firmly tied to the dowels already left in starter with binding wire.

Fixing of Formwork :

The shutters for the pier will be fixed & aligned

depending on the height of pier. Inside surfaces of the forms will be coated with approved release agent. The form work consists of shutters made of steel plates and supported by horizontal and vertical steel walers. The vertical walers are supported by inclined props for alignment control and in turn fixed

to

the

anchor

bolts

embedded in the pile cap. Necessary

working

platform

and access ladders will also be provided. Refer our drawing ‘’ Pier Formwork – General Arrangement‘’ (Drg. No. O5086-Q-BR-CM-GA-0054).


Page 14 of 19



       

The concreting of pier will be done in single pour by

Concreting of Pier :

using boom placer or pump with Tremie / elephant trunk. The placing of concrete will be carried out such

that

segregation,

displacement

of

reinforcement

are

The

pier

compacted

forms

concrete

or

avoided. will

using

be

internal

vibrators to produce a dence homogenous mass. If required windows will be provided in form work to ensure proper compaction. Curing will be done as per the specifications for required period of time.

Deshuttering :

The side forms will be removed after concrete attains

sufficient strength. Care will be taken while removing the formwork such that no damage is caused to the concrete and surface finishes.


Page 15 of 19



        7.7. Erection of I-Girders It is proposed to do the erection by using gantries. The stacked girders will be

transported by long bedded trailers from the stacking yard to erection

location. At the erection location the girders will be lifted from trailers and placed in its location on pier by gantries. The necessary supporting brackets for supporting the I Girders will be provided from the pier cap. The scheme for I Girder erection using gantry is shown in our drawing no: O5086-Q-BRCM-GA-0101.


Page 16 of 19



        7.8. Diaphragm & Deck Slab Casting After completing the erection of girders in one span the formwork and reinforcement for diaphragm will be placed and concreted. Precast planks between the girders for deck slab will be placed. Reinforcement for deck will be tied and concrete for slab will be placed by placer boom. For cantilever deck, steel brackets will be fixed from the end-precast girders for supporting the formwork and the concrete.


Page 17 of 19



       

8. CURING Concrete will be cured by ponding on horizontal surfaces and by continuous water sprinkling with nozzle for vertical surfaces. Water used for curing will be free of any deleterious materials.


Page 18 of 19



       

9. CONCLUSION The

entire

work

will

be

completed within the scheduled time with excellent quality and utmost

safety

methodology document highly

by

using

setout

the

in

this

dedicated

and

experienced

team

of

Engineers.


Page 19 of 19

Method Statement

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