sub surface exploration is done to obtain the information that is useful for one or more of the following purposes
- To select the type and depth of foundation.
- To determine the bearing capacity of soil.
- To calculate the max and differential settlement.
- To determine the properties of water.
- To select the suitable construction technique.
Stages in soil exploration
It is the first step in a sub-surface exploration programme.It includes a visit to the site and study the geological records. It help in deciding future programme of site investigations, scope and methods of exploration.
it is used to determine the depth, thickness and composition of soil strata. It includes few borings or test pits.
The purpose of detailed exploration is to determine the engineering properties of soil by boring, sampling and testing the soil sample in Lab. Some common tests like as field test,vane shear test, plate load test and permeability test are conducted to determine the properties of soil.
Depth of exploration
depth of exploration should be about 1.5 times the width of the square footing and about 3.0 times the width of strip footing. If the footings are closely spaced,the whole load acts as a raft foundation. In this case, the depth of exploration should be at least 1.5 times the width of total area.
Lateral Extent of explorations
For small and less important buildings, one bore hole or a trial pit in the center may sufficient.
For compact building with minimum area of 0.4 hectares, there should be at least 5 bore holes, one at the center and 4 near the corners.
For large buildings, bore hole should be drilled at all the corners and all important locations.