GEOTECHNICAL SITE INVESTIGATION REPORT

 



GEOTECHNICAL SITE  INVESTIGATION REPORT 

TABLE OF CONTENTS

 

S.NO.

CONTENTS


1.0

INTRODUCTION


1.1

PROJECT DESCRIPTION


1.2

PURPOSE OF INVESTIGATION


2.0

FIELD INVESTIGATIONS CONDUCTED


2.1

BOREHOLES PROCEDURE


2.2

GROUND WATER


3.0

LABORATORY TESTS


4.0

SITE CONDITIONS


4.1

SITE STRATIGRAPHY


4.2

GROUND WATER TABLE


5.0

LIQUEFACTION ANALYSIS


6.0

FOUNDATION TYPE & DEPTH


7.0

CONCEPT OF ANALYSYS FOR OPEN / RAFT FOUNDATION


8.0

RECOMMENDATIONS


9.0

CLOSURE


----------PROFILE


----------FIGURES



INTRODUCTION


 

PURPOSE OF INVESTIGATION

The purpose of this study is to investigate the stratigraphy at the Site and to develop geotechnical recommendations for foundation design and construction. To achieve these purposes, the following study was conducted at the site.

(a)         Drilling 2 boreholes (BH-12 & BH-13) to 15 m depth, or Refusal (N>100) whichever met earlier, through Soil and to collect disturbed and undisturbed Soil samples.

(b)         Laboratory testing for selected Soil samples to determine different properties of the Soils.

(c)         Analyzing all field and laboratory data in order to develop engineering recommendations for foundation design and construction.

(d)         Preparation and submission of technical report.

 

                FIELD INVESTIGATIONS CONDUCTED

Locations   of   Boreholes    have   been   marked   at the site as per the approved drawing provided by the client to us. These locations have been marked as BH-12 & BH-13.

 

BOREHOLES PROCEDURE

 

The boreholes were progressed to the specified depth of

15.0 m. The work was done in accordance with IS: 1892-1979

Standard Penetration Tests (SPT) were conducted in the borehole at 1.5 m interval by connecting a split spoon sampler to ‘A’ rods and driving it by 45 cm using a 63.5 kg hammer falling freely from a height of 75 cm. The tests were done in accordance with IS: 2131-1981.

 

The number of blows for each 15 cm of penetration was recorded. The blows required to penetrate the initial 15 cm of the split spoon for seating the sampler is ignored due to the possible presence of loose materials or cuttings from the drilling operation. The cumulative number of blows required to penetrate the balance 30 cm of the 45 cm sampling interval is termed the SPT value or the ‘N’ value.

 

Disturbed samples were collected from the split spoon after conducting SPT. The samples were preserved in transparent polythene bags.

 

Undisturbed samples were collected by attaching a 100 mm diameter thin walled ‘Shelby’ tubes and driving the sampler lightly using a 63.5 kg hammer in accordance with IS:2132 .

 

                GROUND WATER

 

Groundwater level in the boreholes was recorded after 24 hours after drilling was completed. It is mentioned in the borehole logs attached with the report.

 

3.0     LABORATORY TESTS

 

The following table presents the various tests conducted on Soil samples in the laboratory

LABORATORY TEST

IS : CODE REFERRED

Bulk Density

By Calculations

Natural moisture content

IS : 2720 (Part-2)-1973, RA- 2015

Specific Gravity Test

IS : 2720 (Part-3)-1980, RA- 2016

Grain size analysis

IS : 2720 (Part-4)-1985, RA- 2015

Liquid & Plastic limit

IS : 2720 (Part-5)-1985, RA- 2015

Direct Shear Test

IS : 2720 (Part-13)-1986, RA- 2016

Triaxial shear test-Unconsolidated Undrained (UUT)

IS : 2720 (Part-11)-1993, RA- 2007

All test Results are being presented at Table no 1 to 2 of soil profiles & Fig. No. 3 to 12 attached in the report.


SITE CONDITIONS

                SITE STRATIGRAPHY


A fill is met at the site to about 1.0 m depth. Below fill, Clayey Silt (CI) is met to about 6.0 m depth underlain by Silty Sand (SM) / Fine Sand (SP-SM) to the final explored depth of 15.0 m depth.

 

The SPT values range from 4 to 24 to about 5.0m depth. Below this, the SPT values range from 52 to 100+ to the final explored depth of 15.0 m.

 

GROUND WATER TABLE

 

Groundwater was encountered to about 3.0-4.0 m depth below ground surface during field investigation (April, 2022). Fluctuations may occur in measured water table due to variation in rainfall and surface evaporation rates.

5.0     LIQUEFACTION ANALYSIS

 

As per IS 1893-2002, liquefaction is likely in Sand strata below water table for SPT values less than 15. At this Site, Groundwater was encountered to about 3.0-4.0 m depth. The Soils classify Clayey Silt (CI) / Silty Sand (SM) / Fine Sand (SP-SM).

 

The SPT values range from 4 to 24 to about 5.0m depth. Below this, the SPT values range from 52 to 100+ to the final explored depth of 15.0 m.

On review of all Soil parameters like, SPT values, Soil gradation, etc., we are of the opinion that the liquefaction is not likely to take place at this site.

 

6.0     FOUNDATION TYPE & DEPTH

Reviewing the Site Stratigraphy, SPT ‘N’ values & laboratory test results, we recommend that Isolated Open Spread foundation or Raft foundation at or below 3.0 m depth below the existing ground surface may be provided at the Site to support the Structural loads. Recommendations for Isolated/Raft foundations are provided in section 8.0 of this report.

7.0     CONCEPT OF ANALYSIS FOR OPEN/RAFT FOUNDATION

Bearing capacity analysis for Open Spread foundations / Raft foundation have been done in general accordance with IS: 6403-1981. For the Soil conditions encountered at this Site, average of local and general Shear failure conditions has been used for analysis.

Settlement analysis has been performed based on the SPT values as per chart given in IS: 8009 (Part-I)-1976. As per IS 1904-1986, the tolerable total Settlement is taken as 50 mm for Isolated Open Spread foundation or Raft foundation. Appropriate values have been substituted into the bearing capacity equation given in IS-6403 to compute the Safe net bearing capacity. The values have been checked to determine the Settlement of the foundation under the safe bearing pressure. The allowable bearing pressure has been taken as the lower of the two values computed from the bearing capacity shear failure criterion as well as that computed from the tolerable Settlement criterion. The same has been recommended for the design.

8.0     RECOMMENDATIONS

The following table presents our recommended values of Net allowable bearing pressure for 2-5m wide Isolated Open Spread foundations or Raft foundations (width>6.0m) bearing at or below 3.0 m depth below the existing ground surface.

 

Foundation Depth below existing ground level, m

Recommended Net Allowable Bearing Pressure, T/m²

3.0

10.2

3.5

11.3

4.0

13.5

 

The above values include a safety factor of 2.5. Total Settlement of foundation designed for the above net bearing pressure is expected to be about 50 mm. Net bearing pressure for foundations at intermediate depths may be interpolated linearly between the values given above.

9.0    CLOSURE

We are thankful to client to provide the opportunity to perform this investigation by us. We have pleasure in submitting this report. Please contact us when we can be of further service to you.





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