KWANG SING ENGINEERING PTE LTD - Urban ... SING ENGINEERING PTE LTD KWANG SING ENGINEERING PTE LTD (4) KS07/URA-011 After shearing, stop the test, taken out the specimens from the

KS07/URA-017

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KS07/URA-011 (1)

1. INTRODUCTION

This report represents the soil investigation works at Choa Chu Kang Drive. The objective of the soil investigation is to obtain soil parameters for the foundation design. Soil investigation at the site started on 20th December 2007 and finished by 27th January 2008.

2. SCOPE OF WORK

Soil investigation work included drilling, soil sampling, site testing and laboratory testing. A total of five (5) nos. of boreholes were drilled. Site works included SPT test, collection of SPT samples, disturb samples, and UD samples. Laboratory testing work included physical properties of soil tests, Unconsolidated Undrained Triaxial Compression Strength Test and Unconfined Compression Strength Test on rock samples. SPT tests were carried out immediately after taking the undisturbed soil sample and subsequently at an interval of 3m up to 100 blows/30cm were achieved. Generally, boreholes were terminated after achieving SPT ‘N’ values of 100 blows or upon encountering rock. SPT samples were collected by split barrel sampler. Disturb samples were also collected for soil type verification. At least 4 nos. of UD samples were collected at each of the boreholes. UD samples were tested for moisture content, bulk density and Unconsolidated Undrained Triaxial Compression Strength Test and Mechanical Analysis for all the boreholes. All UD samples were sent to Lab Services Private Limited.

3. METHOD STATEMENT

3.1 Site Investigation

Field works included Drilling, SPT test, Disturb and SPT samples sampling, and UD samples sampling.

3.1.1 Drilling

Hydraulic feed rotary boring machine was used for drilling work. A cutting tool was attached at the lower end of the drilling rod. Drilling was carried out by continuously rotating the drilling rod and pumping mud water through hollow rods into the bottom of the boreholes. The cutting was washed out to the ground surface by the water under circulation.


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3.1.2 Standard Penetration Test

SPT test was done in accordance with BS. 5930: 1999. SPT samples were collected for the soil type identification. Prepared the spilt barrel sampler, drive rod, and drive assembly. Clean out the borehole carefully to the test elevation. Withdraw the drilling tools slowly. Lower the split barrel assembly to the bottom of the borehole on the drive rods with the drive assembly on top.

Recorded the initial penetration under dead-weight and if penetration is over 450mm, record the N value as zero. If less than 450mm, continue seating drive and test drive. The hammer (63.5kg mass) was dropping free fall on to a drive head from a height of 760mm and recorded the number of blows to achieve 150mm penetration or 25 blows whichever is first reached as seating drive.

Count the number of blows required for a further penetration of 300mm and recorded as penetration resistance (N) value. If the 300mm penetration could not be achieved in 100 blows, terminate the test drive and recorded the depth of penetration.

3.1.3 Undisturbed Sample Sampling

Undisturbed samples were collected by 75mm thin-wall sampler. Borehole was flushed with water to remove the remnants left at the bottom of the borehole. The depth of the borehole was measured. The sampling tube was lowered to the bottom of the hole and jacked into the soil. After sampling tube was jacking into the soil of required depth, sampler tube was taken out from the borehole, cleaned and sealed with wax at both ends of the sampling tube. The sample identification was then labeled properly.


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3.2 Laboratory Testing

3.2.1 Moisture Content and Bulk Density Test

Moisture content and Bulk Density tests were tested in accordance with BS. 5930: 1999. Initial weight of original sample was measured and dried in the oven under 105 to 1100C until constant weight was achieved. The dry weight of sample was measured and the moisture content was calculated.

(Weight of Wet Sample) – (Weight of Dry Sample) Moisture Content = Weight of Dry Sample Bulk density is the ratio of mass over volume. Specimen was cut by the cutting ring and the weight and volume was measured. Bulk density was calculated as follow: Bulk Density = Weight of Sample Volume

3.2.2 Unconsolidated-Undrained Shear Strength Test

Unconsolidated-undrained Shear Strength test was done in accordance with BS. 5930: 1999. Soil samples were extruded from the UD sample tube into 38mm diameter sample tube. Then, pushed out from the tube and cut top and bottom of the specimen to get 76mm length. Lengths and weight of the specimens were measured. Prepared specimens were set-up in the Triaxial cells. Placed the rubber membranes on the specimens and sealed by the O-rings. Assembled the Triaxial cell, then fill up the cell with water. Fit the proving ring and displacement transducer. Three different cell pressures (0.5σ

′, σ′, and 2σ′ ) were chosen and applied the cell pressures

on the specimens with black pressure drainage lines were closed. Choose the strain rate that failure stress achieved within a period of 5 to 15 min. Then started shearing on specimen at constant strain rate up to deviator stress reached maximum or 20% axial strain was reached.


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After shearing, stop the test, taken out the specimens from the Triaxial Cells. Then, recorded failure modes and measured the specimen moisture contents. 1) Axial Strain

ε = ∆ L L0

∆L = Change in Height of Specimen L0 = Initial Height of Specimen 2) Average Cross Sectional Area

A = Ao 1 – ε

Ao = Initial Average Cross-sectional Area of the specimen 3) Deviator Stress σ1 - σ3 = P

A P = Measured Applied Axial Load A= Average Cross-Sectional Area 4) Shear Strength

Cu = ½ (σ1 - σ3)


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4. RESULT OF SOIL INVESTIGATION

4.1 Sub-soil Condition Six types of soil were encountered at this site. These were:- 1) sandy SILT 2) clayey SILT 3) silty CLAY 4) sandy CLAY 5) SILT 6) SILT with gravel The top soil layers were mainly sandy SILT and clayey SILT. The second soil layers were firm to very stiff sandy CLAY or sandy SILT. Very stiff SILT with gravel was found only in BH4. Bottom soil layers were very dense silty SAND. Rock core of GRANITE was retrieved in BH1. Details of soil layers can be seen in Borehole logs. The borehole-logs and the Probable Soil Profile are attached in Appendix B.

4.2 Water Level Monitoring No water standpipe was installed.

4.3 Laboratory Test Result Laboratory tests were done on the undisturbed samples. Based on the soil testing, moisture contents were found within the range of 273% to 60%, and bulk densities were within 1.60Mg/m3 to 1.94Mg/m3. The cohesion values of the UU tests vary from 19kN/m2 to 152kN/m2. The details were summarized in the laboratory test result summary sheets. Test results are attached in Appendix C.


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5. CONCLUSION

Seven types of soil and rock were encountered at this site. According to the Geological Map of Singapore (PWD 1976) and the types of soil encountered, it may conclude that soils of Bukit Timah Granite Formation were distributed in that area.

______________________________

Joseph C M Lee BSc(Eng) C.E. MICE MIHE MHKIE Managing Director

APPENDIX A

LOCATION PLAN / BOREHOLE LOCATION PLAN

APPENDIX B

PROBABLE SOIL PROFILE / BORELOG

APPENDIX C

LABORATORY SOIL TEST REPORT

KWANG SING ENGINEERING PTE LTD - Urban ... SING ENGINEERING PTE LTD KWANG SING ENGINEERING PTE LTD (4) KS07/URA-011 After shearing, stop the test, taken out the specimens from the

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