SUB SURFACE EXPLORATION AND IN-SITU TESTING
DISCUSSION ON FIELD AND LABORATORY TESTS
SAFE BEARING CAPACITY
CONCLUSIONS AND RECCOMENDATIONS
The appropriate scope of a geotechnical investigation is a function of the type of proposed land use or project, the soil/ geologic conditions of the project site, and type of permit or approval sought. The geotechnical consultant is responsible for targeting the scope of their investigation, testing, analyses, and documentation to balance these factors. References are given wherever required. 2.
The objective of the exploration work was to determine the probable sub surface conditions such as stratification, denseness or hardness of the strata, position of ground water table etc. and to evaluate probable range of safe bearing capacity and shear strength for the structure.
To fulfill the objective, the work carried out is comprises of:
• Drilling one borehole up to the depth of 10.0m below existing ground level in order to know the sub surface stratification, conducting necessary field tests and to collect disturbs and undisturbed soil samples for laboratory testing.
• Testing soil samples in the laboratory to determine its physical and engineering properties of the soil samples, and Page 2
• Analyzing all field and laboratory data to evaluate safe bearing capacity and shear strength of the soil for given foundation sizes and necessary recommendations for foundation design and construction.
The structure is located at JDA-13 Location near Balnaba Village, Bhuj
Sub Surface Exploration And In-Situ Testing:
The actual investigation work was started on 18/02/2010 and was completed on 19/02/2010. The work was done in the following manner -
One borehole of 150mm diameter is drill up to the depth of 10.0m. Where caving of the borehole occurred, casing was used to keep the borehole stable. The work was in general accordance with IS: 1892 – 1979. The borehole is located at the center of the wind mill foundation.
3.1.1 Disturbed Samples: Disturbed representative samples were collected, logged, labelled and placed in polythene bags.
3.1.2 Undisturbed Samples: Undisturbed soil samples are collected in 100 mm diameter thin walled sampler (Shelby tube) from the borehole. The sampler used for the sampling had smooth surface and appropriate area ratio and cutting edge angle thereby minimizing disturbance of soil during sampling. Samples are logged and labelled properly and transfer to the laboratory for further testing.
3.1.3 Water Table: Water table was encountered during the sub soil exploration work carried out in the month of February 2011.
3.2 Standard Penetration Test
The standard penetration tests are conducted in each bore as per IS: 2131: 1981 (Reaffirmed 2002). It is ensured that the energy of the falling weight is not reduced by friction between the drive weight and the guides or between ropes. The rods to which the sampler is attached for driving are straight, tightly coupled and straight in alignment. Thereafter the split spoon sampler is further driven by 30cm. The number of blows required to drive each 15cm penetration is recorded. The first 15cm of drive considered as seating drive. The total blows required for the second and third 15cm penetration is termed as a penetration resistance - N value. The N-values for each bore hole are given in the following table 3.3 Vane shear Test (VST): Vane Shear tests are conducted in the boreholes when the soil has very low shear strength or SPT penetration resistance “N” is less than or equal to 1. In-Situ Vane Shear Test for soils is conducted as per IS-4434. In this test when the borehole was drilled till the test depth the vane of 50 mm size was attached to the rods and lowered in the borehole to the test depth. The vane was pushed...
References: 3.2 Standard Penetration Test
The standard penetration tests are conducted in each bore as per IS: 2131: 1981 (Reaffirmed 2002)
3. Atterberg 's limit - (IS 2720 part – 5 1985)
5. Shear test [Direct and Tri-axial Test] - (IS 2720 part – 11 1986)
7 Free swell and Swell pressure test - (IS 2720 part – 40 1977, part – 41 1977))
All laboratory tests are carried out as per the respective Indian Standards.
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