The water table has marked influence on the bearing capacity of sandy or gravelly soil. If the water table is already above the, level of footing, it should be lowered by pumping and the bearing plate seated after the water table has been lowered just below the footing level. Even if the water table is located above 1 m below the base level of the footing, the load test should be made at the level of water table itself.
The load intensity and settlement observations of the plate load are plotted as shown in Fig. 2.24 (a). Curve I corresponds to general shear failure and curve II corresponds to local shear failure. Curve III is a typical of dense cohesionless soils which do not show any marked shear failure under the loading intensities of the test.
When the load settlement curve [Fig. 2.24 (a)] does not indicate any marked breaking point, failure may alternatively be assumed corresponding to a settlement equal to one-fifth of the width of the test plate. In order to determine the safe bearing capacity it would be normally sufficient to use a factor of safety of 2 or 2.5 on utlimate bearing capacity.
FIG. 2.24 LOAD SETTLEMENT CURVES.