Soil testing is required for the deep foundation. It is necessary to ensure the bearing capacity of the soil to support the loads from the deep foundation. Deep foundations are the depth of foundation which is generally greater than two times the width of footing. Deep foundations are required due to different reasons. Here, we have discussed the types of soil tests need to perform for deep foundations.
Direct Shear Test
This test is conducted to estimated the effective friction angle of cohesionless soil. Nonetheless, there are correlations that are developed to evaluate the effective friction angle of cohesionless soil.
A Standard Penetration Test (SPT)
This test is performed to determine the cohesion (and consequently the adhesion) to determine the angle of friction (and consequently the angle of friction between soil and the pile and also the point of resistance) for each soil stratum of cohesionless soil of soil.
A Static Cone Penetration Test (CPT)
This test is conducted to determine the cohesion (and subsequently the adhesion) for soft cohesive soils and to check with SPT results for fine to medium sands. For the strata encountering both cohesive and cohesion-less soils, both SPT and CPT tests are required.
Vane Shear Test
This test is performed to the estimated undrained in-situ shear strength of impervious clayey soils.
Undrained Triaxial Shear Strength
This soil test is carried out on undisturbed soil samples (obtained with thin-walled tube samplers) to determine cohesion and angle of internal friction for clayey soils. Procedures for conducting this test are provided by ASTM D 2850–03, 2004. In the case of driven piles proposed for stiff clays, it is necessary to check with the cohesion and angle of internal friction from re-molded samples. Drained shear strength parameters are also determined to represent the in-situ condition of the soil at end of the construction phase.
Pressure Meter Test
This test is performed to determine the stress-strain curve of horizontal loading. The equipment is either inserted into a pre-drilled borehole or a self-boring pressure meter is used. Unless the soil is isotropic, the same value cannot be adopted for the vertical direction. This test is performed specifically for piles that are subjected to lateral loading.
Ground Water Condition and Permeability of the Soil
Groundwater conditions and soil permeability influence the choice of pile type to be recommended. Hence the level at which water in the borehole remains is noted in the bore logs. Since the permeability of clay is very low, it takes several days for the water in the drill hole to rise up to the groundwater table. Groundwater samples need to be tested to consider the possible chemical effects on concrete and the reinforcement. The result of the cone penetration test for the same soil shows substantial scatter. They need to be checked with supplementary information from other exploration methods.
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