GEOTECHNICAL INVESTIGATION REPORT (APRIL 2012)

PROPOSED BUILDING

WALLFORT CITY RING ROAD NO. 1

BHATAGAON, RAIPUR, CHATTISGARHFOR M/S CHATTISGARH PROJECT PVT. LTD.

Table of Contents

Item Page 1.0 INTRODUCTION 1

2.0 EXPLORATION PROGRAM 1

2.1 Exploration Scope 1 2.2 Subsurface Conditions 2 2.3 Groundwater Levels 3

3.0 FOUNDATION RECOMMENDATIONS 4

3.1 Foundation Protection 5

4.0 FIELD EXPLORATION PROCEDURES 6

ANNEXURES 7

Figure 1: Borehole Location Plan Borehole Logs Laboratory Test Results References/Calculations

GEOTECHNICAL INVESTIGATION REPORT (APRIL 2012) PROPOSED BUILDING

WALLFORT CITY RING ROAD NO. 1

BHATAGAON, RAIPUR, CHATTISGARH

FOR M/S CHATTISGARH PROJECT PVT. LTD.

1.0 INTRODUCTION

Chattisgarh Project Pvt. Ltd. plans construction of a building in Raipur, Chattisgarh. The

proposed building will consist of a single basement, ground and up to 10 upper floors. The

work of geotechnical investigation was awarded to M/s. Earth Engineering. The field work

and laboratory tests for the geotechnical investigation were completed by Earth Engineering

in April 2012. This report prepared by Geocon International Pvt. Ltd. presents results of the

geotechnical investigation along with foundation recommendations for the proposed

building.

2.0 EXPLORATION PROGRAM

2.1 Exploration Scope

Ten Boreholes (BH-1 to BH-10) were completed for the project as illustrated on the Borehole

Location Plan in the Annexure.

2

2.2 Subsurface Conditions

Subsurface profile at this site generally consists of residual soils underlain by Bedrock.

Encountered soil/rock layers are described below;

LAYER I: RESIDUAL SOILS

Residual soils, consisting mostly of Brown sandy clay with boulders, were encountered from

the ground surface in the boreholes. This layer is formed by the complete in-place

disintegration of parent bedrock material to texture of soils. Based on Standard Penetration

Tests (SPT), consistencies of the cohesive soils within this layer was stiff. The lower

boundary of this layer was encountered at depths between 1.5m and 4.5m below ground

surface.

LAYER II: MUDSTONE / LIMESTONE BEDROCK

Brown Mudstone or Limestone bedrock was encountered at depths between 1.5m and 4.5m

below ground surface in the boreholes. The bedrock was typically highly weathered. Core

Recoveries varied between 22% and 95%, generally improving with depth, while Rock

Quality Designation (RQD) ranged between 0 and 80%. Compressive strength of rock core

samples, based on point load index tests and Unconfined Compression Tests on rock

3

samples ranged between 22 kg/cm2 and 1073 kg/cm2. The boreholes were terminated in

this bedrock layer at depths between 6.5m and 10.0m below ground surface.

2.3 Ground water Levels

Groundwater accumulation in boreholes was monitored during and after completion of

drilling activities. Groundwater was not encountered in any of the boreholes. Seasonal and

annual fluctuations in ground water levels can be expected.

4

3.0 FOUNDATION RECOMMENDATIONS

Bedrock was encountered at depths between 1.5m and 4.5m below ground surface at this

site. Soft weak Mudstone bedrock was encountered in boreholes BH-6 and BH-7.

Spread/raft foundations for proposed building with single basement supported on this soft

weathered bedrock, can be designed for a maximum gross allowable bearing capacity of 50

t/m2.

Hard limestone bedrock was encountered in the remaining boreholes. Spread foundations

for proposed building near these remaining boreholes can be designed for a much higher

gross allowable bearing capacity of 300 t/m2.

The exact areas of soft rock and hard rock should be delineated upon excavation of building

foundations, if the above two separate bearing capacities are adopted.

Minimum footing width should be 1.0m. Maximum settlement of foundations will be less

than 12mm. Modulus of subgrade reactions of 4,000 t/m3 and 30,000 t/m3 can be utilized

for design of foundations installed on soft rock and hard rock, respectively.

5

3.1 Foundation Protection

Results of chemical analysis on groundwater samples enclosed in the Annexure, indicate

that the site falls under Class 1 for sulphate and chloride concentrations (As per IS456 and

as per CIRIA Sp. Publication No. 31). A ‘mild’ Exposure Condition was assigned to this site.

Therefore only following normal precautions are recommended to protect subsurface

concrete and reinforcement.

Type of Cement: OPC or PPC

Minimum Grade of Reinforced Concrete: M20

Minimum Cement Content for spread footings: 300 kg/m3

Maximum Water Cement Ratio: 0.50

Minimum Cover to Reinforcement: 50mm

6

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 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,

GEOCON INTERNATIONAL PVT. LTD.

__________________________________ Jaydeep Wagh B.E., M.S., P.E. (Geotechnical)

REFERENCES

1) Foundation Analysis and Design, J.E. Bowles, McGraw Hill Publication, 5th Edition, 1996.

2) Canadian Foundation Engineering Manual.

3) Soil Mechanics in Engineering Practice, 2nd

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.

8

SAMPLE CALCULATION OF ALLOWABLE BEARING CAPACITY

FOR FOUNDATIONS ON HIGHLY WEATHERED BEDROCK (BOREHOLES BH-6 AND BH-7)

________________________________________________ GL +0.0m

Layer I, Residual soils (Clay) ________________________________________________ -1.5m to -2.5m Layer II, Highly Weathered Mudstone Bedrock

(Assuming Highly weathered Bedrock to be a very dense granular soil.)

Net Ultimate Bearing Capacity = qu = cNc + q (Nq – 1) + 0.5 B γNγ sγ (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 = 1m

γ’ = submerged unit weight of soil = 1.80

Nc, Nq, Nγ = Terzaghi’s Bearing capacity factors

Sc, sq, sγ = Shape factors = Conservatively assumed as 1.2, 1.2, and 0.6, respectively D = Depth of Footing below basement top = 1.5m

Minimum SPT N value obtained in boreholes = 50 Corresponding friction angle = 40

o (Reference No. 5)

Corresponding Nc=75, Nq=64, Nγ=109 (Reference 5, IS:6403-1981);

Substituting these values in the above equation; q ultimate =qu =[0x75x1]+[1.5x1.8x(64-1)x1]+[0.5x1x0.8x109x0.6]= 0+150+25 = 175 t/m

2

q safe = qu/F.S. = 175/2.5 = 70 t/m2

Restricted to 50 t/m2 to limit settlements as shown below.

9

CALCULATION OF SETTLEMENTS OF FOUNDATIONS (3M X 3M) EXERTING

PRESSURE OF 50 T/M2:

Net pressure exerted by foundations = 50 t/m2 – weight of soil removed by basement = 45 t/m2

From Reference No. 1:

Settlement = S q BE

mI Is

s f=−

0

21'

µ

Where, q0 = Footing Pressure = 45 t/m2 B’ = B/2 (Where B is the width of pressure distribution

� = 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=6m, and D=3.5m Therefore, M=L/B=1; and N=H/B’=4 and D/B=1.1

Corresponding, Is = 0.43, Conservative If = 1.0 (From Table 5-2, Reference 1)

Settlement of Layer = S1 = 0.143.049250

3.015.145

2

xxxxx−

= 0.014m = 14mm

From IS8009:

Due to Depth Factor, Settlement = 0.8 x 14mm = 12mm

Therefore, Total Settlement = 12mm

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WALLFORT HEIGHT