PERF E C T GEOTECHNICS P V T . L T D. 24, Maruti Paradise, Sector 15, CBD Belapur, Navi Mumbai-400614. Tele.: 27570146, Fax: 27570147. e-mail:
[email protected]
FINAL GEOTECHNICAL INVESTIGATION REPORT FOR PROPOSED RESIDENTIAL COMPLEX AT ROHINJAN, TALOJA, NAVI MUMBAI, FOR ADHIRAJ CONSTRUCTION PVT. LTD.
Table of Contents
Item
Page
1.0
INTRODUCTION
1
2.0
EXPLORATION PROGRAM
2
2.1 2.2 2.3
3.0
4.0
Exploration Scope Subsurface Conditions Groundwater Levels
FOUNDATION RECOMMENDATIONS
2 4 5
6
3.1 Foundation Protection
9
FIELD EXPLORATION PROCEDURES
10
ANNEXURES
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Figure 1: Borehole Location Plan Borehole Logs Subsurface Profile Laboratory Test Results References/Calculations
FINAL GEOTECHNICAL INVESTIGATION REPORT FOR PROPOSED RESIDENTIAL COMPLEX AT ROHINJAN, TALOJA, NAVI MUMBAI, FOR ADHIRAJ CONSTRUCTION PVT. LTD.
1.0 INTRODUCTION
Adhiraj Construction Pvt. Ltd. plans construction of a residential complex in Taloja, Navi Mumbai. M/s. VMS Consultants is structural consultant and Edifice Consultants Pvt. Ltd. is architect for the project. The proposed complex will consist of G+13, G+15, G+30 and G+40 storied structures. The work of geotechnical investigation was awarded to Perfect Geotechnics Pvt. Ltd.
The field work and laboratory tests for the Geotechnical
Investigation were completed by Perfect Geotechnics Pvt. Ltd. in January 2011. This final report presents results of the geotechnical investigation with foundation recommendations for the proposed buildings. 1
2.0 EXPLORATION PROGRAM
2.1 Exploration Scope
Forty five Boreholes (BH-1 to BH-45) were completed for the project as illustrated on the Borehole Location Plan in the Annexure. Borehole termination depths and structures are summarized in table A below.
TABLE A BOREHOLE TERMINATION DEPTHS & STRUCTURES Structure Depth of Termination BH. No weathered depth of borehole bedrock Below Ground Surface BH-1 0.7m 15.50m BH-2 0.5m 10.40m BH-3 1.0m 13.20m BH-4 3.0m 12.20m BH-5 1.0m 12.25m BH-6 1.0m 7.90m BH-7 3.0m 15.40m BH-8 0.8m 15.40m G+13 BH-9 0.9m 15.25m BH-10 3.5m 10.80m BH-11 2.0m 15.55m BH-12 4.0m 9.60m BH-13 4.0m 10.50m BH-14 0.7m 14.55m BH-15 2.5m 11.07m BH-16 1.5m 9.73m BH-17 G+40 1.5m 13.70m BH-18 G+15 5.0m 11.60m BH-19 G+40 1.5m 8.30m BH-20 G+30 1.5m 12.60m BH-21 G+40 4.5m 14.50m BH-22 0.7m 10.90m BH-23 0.7m 15.10m BH-24 0.6m 10.20m BH-25 1.0m 16.80m BH-26 1.0m 10.00m BH-27 G+40 0.7m 9.50m BH-28 0.8m 10.00m BH-29 1.0m 14.30m BH-30 0.3m 15.20m BH-31 0.0m 10.10m BH-32 0.2m 15.10m 2
BH-33 BH-34
3.0m 9.00m 1.0m 17.18m TABLE A (Contd) BOREHOLE TERMINATION DEPTHS & STRUCTURES Structure
BH. No
Depth of weathered bedrock
Termination depth of borehole Below Ground Surface
BH-35 BH-36 BH-37 BH-38 BH-39 BH-40 BH-41 BH-42 BH-43 BH-44 BH-45
0.1m 0.5m 1.9m 1.5m 0.0m 2.0m 1.5m 1.0m 3.0m 1.0m 1.5m
9.85m 15.30m 7.70m 8.40m 9.20m 9.20m 9.70m 15.40m 8.50m 9.30m 15.85m
G+40
2.2 Subsurface Conditions
Subsurface profile at this site generally consists of black clay overlying completely weathered bedrock underlain by hard bedrock. described below;
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Encountered soil/rock layers are
LAYER I: BLACK CLAY Black clay was encountered at the ground surface in majority of the boreholes. Thickness of this layer varies between 0.10m and 2.1m. This layer is potentially expansive.
LAYER II: COMPLETELY WEATHERD ROCK Completely weathered bedrock was encountered at depths between 0.0m and 2.1m below ground surface. This layer is formed by the complete in-place disintegration of parent bedrock material, but still partially retains the original rock mass structure, and is also locally referred to as hard murrum.
SPT tests conducted in this layer encountered
refusals. Core recoveries were typically less than 35 percent. The lower boundary of this layer was encountered at depths between 1.0m and 7.0m below ground surface.
LAYER III: HARD BASALT BEDROCK Hard Basalt bedrock was encountered at depths between 1.0m and 7.0m below ground surface in the boreholes. The bedrock was highly weathered to sound. Core Recoveries varied between 37% and 100%, while Rock Quality Designation (RQD) ranged between nil and 100%. Compressive strength of rock core samples ranged between 53 kg/cm2
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and 801 kg/cm2. The boreholes were terminated in this bedrock layer at depths between 7.7m and 17.18m below ground surface.
2.3 Ground water Levels Groundwater accumulation in boreholes was monitored during and after completion of drilling activities. Groundwater was observed in boreholes at depths between 0.6m and 2.80m below ground surface. Seasonal and annual fluctuations in ground water levels can be expected.
3.0 FOUNDATION RECOMMENDATIONS Completely weathered bedrock (hard murrum) was encountered at depths between 0.0m and 2.1m below ground surface. Hard rock was encountered at depths between 1.0m and 7.0m below ground surface. Exact depths to completely weathered rock and hard rock are given in Table B below.
Spread/raft foundations for proposed buildings, supported on the completely weathered bedrock at minimum depths of 1.0m and 3.0m, can be designed for net allowable bearing capacities of 45 t/m2 and 60 t/m2, respectively. Spread foundations installed on hard rock
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can be designed for net allowable bearing capacity of 300 t/m2. Light rock breaking with rock breakers will be required to complete excavations in the completely weathered rock. Hard rock founding strata can be identified as it makes a ringing sound when struck with crowbar or bucket excavators. Base of excavations should be manually cleaned of all loose excavated soils/ materials.
TABLE B DEPTHS TO BEDROCK BOREHOL E NUMBER
STRUCTURE
DEPTHS TO CWR CR<35%
BH-1 BH-2 BH-3 BH-4 BH-5 BH-6 BH-7 BH-8 BH-9 BH-10 BH-11 BH-12 BH-13 BH-14 BH-15 BH-16 BH-17 BH-18 BH-19 BH-20 BH-21 BH-22
G+13
0.2m 0.5m 0.15m 0.45m 0.3m 0.2m 0.25m 0.15m 0.15m 0.3m 0.3m 0.3m 0.2m 0.1m 0.3m 0.3m 0.3m 0.5m 0.3m 0.3m 0.25m 0.7m
G+40 G+15 G+40 G+30 G+40 6
DEPTHS TO HARD ROCK CR>35% 4.5m 4.5m 4.5m 6.0m 5.5m 1.0m 4.5m 4.0m 6.0m 5.0m 5.0m 4.0m 6.0m 4.5m 5.5m 4.5m 3.0m 6.5m 3.0m 6.0m 4.5m 4.5m
BH-23 BH-24 BH-25 BH-26 BH-27 BH-28 BH-29
0.7m 0.6m 1.0m 1.0m 0.2m 0.8m 1.0m
G+40
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6.0m 4.5m 7.0m 5.0m 4.5m 3.0m 4.0m
TABLE B (Contd.) DEPTHS TO BEDROCK BOREHOL E NUMBER
STRUCTURE
DEPTHS TO CWR CR<35%
BH-30 BH-31 BH-32 BH-33 BH-34 BH-35 BH-36 BH-37 BH-38 BH-39 BH-40 BH-41 BH-42 BH-43 BH-44 BH-45
G+40
0.3m 0.0m 0.2m 0.3m 0.15m 0.1m 0.5m 1.65m 0.1m 0.0m 0.0m 1.0m 0.0m 2.1m 0.35m 0.3m
G+40
Maximum settlement of foundations will be less than 10mm.
DEPTHS TO HARD ROCK CR>35% 4.5m 4.5m 4.5m 3.5m 5.5m 3.0m 5.0m 1.9m 3.0m 4.5m 3.5m 4.5m 5.0m 4.5m 3.4m 5.2m
Modulus of subgrade
reactions of 4500 t/m3 and 30,000 t/m3 can be utilized for design of foundations installed on CWR and hard rock, respectively. Excavation sides should be sloped at a maximum slope of 1:2 (horizontal: vertical) or flatter. Dewatering will be required in excavations.
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3.1
Foundation Protection
Groundwater samples were collected for chemical analysis from the site.
Results of
Chemical analysis are enclosed in the Annexure. Based on chemical results, the site falls under Class I for sulphates and chlorides (As per IS456-2000 and as per CIRIA Special Publication No. 31). A moderate exposure condition was assigned to this site. Hence, following precautions shall be taken to protect concrete and reinforcement in foundations;
Type of Cement:
OPC or PPC
Minimum Grade of Reinforced Concrete:
M25
Minimum Cement Content for spread footings:
300 kg/m3
Maximum Water Cement Ratio:
0.50
Minimum Cover to Reinforcement:
50mm
4.0 FIELD EXPLORATION PROCEDURES
The sub-surface investigation was completed generally as per IS: 1892-1979. The field investigation was carried out using a rotary machine. Casing was used to support sides of borehole until sufficiently stiff strata was encountered. Standard Penetration Tests (i.e. SPT) were carried out in soil in accordance with IS 2131-1981. Using this procedure, a 2” outside diameter split-barrel sampler is driven into the soil by 63.5 kg. weight falling
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through 75 cm height. After an initial set of 15cm, the number of blows required to drive the sampler an additional 30 cm, is known as the “penetration resistance” or “N value”.
When SPT refusal was obtained in hard strata, rock coring was done using diamond bit and double tube core barrel to obtain rock samples. Percent Rock Core Recovery and Rock Quality Designation (%RQD) were determined. % RQD = 100 x Sum of length of rock pieces in cms, each having lengths greater than 10cms/Total length of core run.
Sincerely, PERFECT GEOTECHNICS PVT. LTD.
__________________________________ Jaydeep Wagh B.E., M.S., P.E. (Geotechnical)
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REFERENCES
1) Foundation Analysis and Design, J.E. Bowles, McGraw Hill Publication, 5th Edition, 1996.
2) Canadian Foundation Engineering Manual.
nd
3) Soil Mechanics in Engineering Practice, 2 Edition, Terzaghi K. and Peck R. B., John Willey and Sons, 1967.
4) Foundation Design Manual, N. V. Nayak, 5th Edition, 1996.
5) IS:6403-1981, Code of Practice for Design and Construction of Shallow Foundations on Soils.
6) IS14593, Code of Practice for Design of Pile Foundations on Rock.
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SAMPLE CALCULATION OF ALLOWABLE BEARING CAPACITY FOR FOUNDATIONS ON COMPLETELY WEATHERED BEDROCK ________________________________________________ GL +0.0m Layer I, Black cotton soils _______________________________________________ -0.0m to -2.10m Layer II, Basalt Bedrock
(Assuming Completely weathered Bedrock to be a very dense granular soil.) Net Ultimate Bearing Capacity = qu = cNc + q (Nq – 1) + 0.5 B N s
(Refn. 5, Table 4-1)
Where, q = Overburden Pressure (i.e. submerged unit weight x depth of foundation) c = Cohesion B = Minimum Width of foundation = 1.5m ’ = submerged unit weight of soil = 0.80 Nc, Nq, N = Terzaghi’s Bearing capacity factors Sc, sq, s = Shape factors = conservatively assumed as 1.2, 1.2, and 0.8 D = Minimum Depth of Footing = 1.0m Minimum SPT N value obtained in boreholes = 50 o Corresponding friction angle = 40 (Reference No. 5) Corresponding Nc=75, Nq=64, N=109 (Reference 5, IS:6403-1981); Substituting these values in the above equation; q ultimate =qu =[0x75x1.2]+[1.0x0.8x(64-1)x1.2]+[0.5x1.5x0.8x109x0.8]= 0+60+52 = 112 2 t/m q safe = qu/F.S. = 112/2.5 =45 t/m2
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CALCULATION OF SETTLEMENTS OF FOUNDATIONS (3M X 3M) EXERTING PRESSURE OF 45 T/M2: A) SETTLEMENT OF CWR FROM – 1.0m to -6.5M From Reference No. 1: Settlement = S q0 B'
1 2 mI s I f Es
Where, q0 = Footing Pressure = 45 t/m2 B’ = B/2 (Where B is the width of pressure distribution μ = Poisson’s ratio = 0.3 E = Modulus of Elasticity Is = Influence Factor (Obtained from Table 5-2, Reference No. 1) If = Depth Factor (Obtained from Figure 5-7, Reference No. 1) m = 4 for center of footing
Very conservatively assuming weathered bedrock within the full influence zone of footings: E value for over-consolidated sand = 105(N)+4000 (Reference No. 1) Therefore, for a SPT N value of 50, E=9,250 t/m2 L’ = 3/2 =1.50, B’ = 3/2 = 1.5, H=5.5m, and D=1m Therefore, M=L/B=1; and N=H/B’=3.67 and D/B=0.33 Corresponding, Is = 0.418, Conservative If = 1.0 (From Table 5-2, Reference 1)
Settlement of Layer =
1 0.3 2 S1 = 45 x1.5 x x 4 x0.418x1.0 = 0.011m = 11mm 9250
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B) SETTLEMENT OF HARD ROCK BELOW -6.5M
From Reference No. 1: Settlement = S q0 B'
1 2 mI s I f Es
Where, q0 = Footing Pressure = 45 t/m2 (after allowing for pressure dissipation) B’ = B/2 (Where B is the width of pressure distribution μ = Poisson’s ratio = 0.2 E = Modulus of Elasticity Is = Influence Factor (Obtained from Table 5-2, Reference No. 1) If = Depth Factor (Obtained from Figure 5-7, Reference No. 1) m = 4 for center of footing E value for Basalt Bedrock = 1700,000 t/m2 Using 1/10th of this value for Basalt Bedrock, E = 0.1 x 17, 00,000 = 170,000 t/m2 Depth of top of layer below footing= 6.5m Assuming a 30 degree pressure dissipation, Width of pressure distribution at top of the layer = 3m + 6.5m = 9.5m Length of pressure distribution at top of the layer = 3m + 6.5m = 9.5m L’ = 9.5/2 =4.5, B’ = 9.5/2 = 4.5, H=6m, and D=6m Therefore, M=L/B=1; and N=H/B’=4 and D/B=0.66 Corresponding, Is = 0.255, Conservative If = 1.0 (From Table 5-2, Reference 1) Settlement of Layer =
S2 = 45 x 4.5 x
1 0.25 2 x 4 x0.255x1.0 = 0.001m = 1mm 170,000
THEREFORE, TOTAL SETTLEMENT = 11mm + 1mm = 12mm From IS8009: Due to Footing Rigidity Factor, Settlement = 0.8 x 12mm = 10mm
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SAMPLE CALCULATION OF ALLOWABLE BEARING CAPACITY OF SPREAD / RAFT FOUNDATIONS SUPPORTED ON BEDROCK
FROM REFERENCE NO. 3: Allowable Capacity = qend = Nj x Qu Where, Nj = Empirical coefficient = 0.1 to 0.4 (conservatively adopted as 0.3 for bedrock) Qu = Representative Compressive strength of rock = 1113 t/m2 Allowable capacity = 0.3 x 1113 t/m2= 339 t/m2 say 300 t/m2
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B) CALCULATION OF SETTLEMENTS OF SPREAD FOUNDATIONS (5M X 5M) EXERTING PRESSURE OF 300 T/M2:
Settlement = S q0 B'
1 2 mI s I f Es
Where, q0 = Footing Pressure = 300 t/m2 B’ = B/2 (Where B is the width of pressure distribution μ = Poisson’s ratio = 0.2 E = Modulus of Elasticity Is = Influence Factor (Obtained from Table 5-2, Reference No. 1) If = Depth Factor (Obtained from Figure 5-7, Reference No. 1) m = 4 for center of footing E value for Basalt bedrock = 17, 00,000 t/m2 th 2 Using 1/10 of this value for Basalt bedrock, E = 170,000 t/m (Reference 7) L’ = 5/2 =2.5, B’ = 5/2 = 2.5, H=10m, and D=3m Therefore, M=L/B=1; and N=H/B’=4 and D/B=0.6 Corresponding, Is = 0.53, Conservative If = 1.0 (From Table 5-2, Reference 1) Settlement of Layer =
S1 = 300 x2.5 x
1 0.2 2 x4 x0.43x1.0 = 0.007m = 7mm 170,000
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