Behaviour of Foundation in Layered Soils

General bearing capacity equations widely used are evolved by several investigators based on the conventional theories derived from the failure pattern of soil. This paper presents the behaviour of foundation resting on layered soils under vertical loading conditions which simulate the field conditions more accurately. The different modes of failure and the deformation patterns of foundation are determined by using finite element modeling. The parameters like thickness of soil layers, angle of friction and cohesion are varied in order to study their effect on failure pattern. The failure patterns of foundations on layered soils are found to be different from those from conventional theory. Different cases like a sand layer overlying clay soil, clay layer overlying sand layer, two clay layers with different values of cohesion were also analyzed by varying the thickness of overlying stratum (d). The failure patterns are explained for each case. In clay overlaying sand layer, the failure of the foundation is occurred mainly due to tilting, with more deflection at d/B =1, where B is the width of foundation. The maximum deflection occurred within the loading region. In sand overlaying clay layer, the displacement gradually decreased when d/B ratio is increased. The displacement is more at beyond the loading region. The stresses are increased gradually up to d/B ratio of 1.5. Failure is mostly by the punching type shear failure. Settlement was found to be reduced as angle of internal friction of the soil is increased. For cohesion ratio, (ratio of cohesion of first layer to second layer) C1/C2 = 0.5 (1) also the failure pattern was found to be by general shear failure.