REQUIREMENTS OF GEOTECH (GEOTECHNICAL) STUDIESA sound and effective geotechnical report for a particular project site should ideally include the following, but not limited to:
- Appraise and analyze the estimated bearing capacities, settlement behavior, swelling potential including settlements versus time charts of foundations for the different strata encountered at different locations of the project site.
- Should indicate recommendations regarding the type of foundations to be provided for different structures with reference to envisaged range of loading building-wise.
- In case piling is envisaged, preliminary data regarding the types, numbers, diameters, depths, etc. for piles under different loading conditions with suitable recommendations should be furnished.
- Recommendations regarding the allowable bearing capacities of different soil and rock strata at different levels and at different locations of the site.
- Assessing and providing site spectra (Time Versus Acceleration Curve).
- Indicate level of water table and seasonal variations.
- Furnish relevant cross-sectional details of soil profile for the entire area so as to enable a study of underlying strata.
- Establishing any corrosive element present in soil along the depth with specific recommendation about safety against corrosion.
- Indicate setting out and marking of all the test locations, showing the levels of the existing ground level at the test locations.
GENERAL TRADE SPECIFICATIONS FOR CARRYING OUT THE WORKA civil engineer must be aware of the broad technical specifications that are usually put in use during a detailed soil investigation. The major of them are furnished hereunder for his/her ready reference:
Boreholes are drilled through all types of soil and rock strata at locations indicated in the drawing showing test points. The depth of the boreholes depends largely upon the type of strata encountered, and the envisaged structure loading at that point. In case hard rock (SPT > 100) is encountered at shallow depths itself, the boreholes can be terminated after drilling 3m inside the hard rock. The exact depth of the boreholes is usually determined at site by the concerned engineers after taking into considerations the soil/rock strata encountered.
A detailed borehole log should be maintained for all the boreholes. These bore-logs provide the essential spectrum of the strata encountered, which in turn, help in deciding the type of foundations required.
Trial pits are open excavations carried up to approximate depths of 1 to 2 meters so as to ascertain the settlement properties of the excavated soil pits with certain calibrated loadings.
Field density and bulk density tests should be conducted for each different stratum encountered, and a proper log should be maintained.
Sampling is done for two cases: Disturbed samples & Un-disturbed samples.
The samples are collected from boreholes, plate load test pits and trial pits, which are then analyzed in the laboratory for various soil properties like moisture content, specific gravity, grain size analysis, Atterberg's limits, pH value, sulphate & chloride content, etc.
SUMMARIZING & REPORTINGAfter conducting all the relevant studies and tests, the results of all the above laboratory tests should be incorporated in the soil investigation report, which should be referred by the design engineers for designing the buildings and the structures.
The test results should be properly tabulated in the report together with the origin of the sample on which the test has been conducted. All necessary calculations and graphs shall also be included in the report for ready reference.
INFERENCEThe relevance of a systematic and sound soil investigation report can be understood from the basic point that no practical and economized design of the buildings and structures can be done without taking the inferences from this report. As such, the engineers & technicians should be familiar with the requirements of such an investigation.
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