Bearing Capacity of Embedded Strip Footings in Two-Layered Clay Soils

This paper studied the effect of embedment on the ultimate bearing capacity of rigid strip footings embedded in two-layered clay soils with relatively different shear strengths. The ultimate collapse loads were calculated using the finite element method. A parametric study was performed for a relative depth of embedment D/B varying from 0 to 1 (where D and B are the footing embedment and width respectively), relative thickness of the top clay layer H/B from 0.125 to 4, and strength ratio of the two clay layers c_u1/c_u2 from 0.5 to 7, where c_u1 and c_u2 are the undrained shear strengths of the upper and lower clay layers respectively. The finite element results were presented in terms of a modified bearing capacity factor that accounts for the footing embedment and the relative shear strength and thickness of the two clay layers. The finite element results for surface strip footings and embedded footings in homogeneous clay were within the narrow ranges defined by the rigorous lower and upper bound solutions available in the literature. The finite element results for embedded footings were compared with those obtained using approximated bearing capacity equations for two-layered clay soils. The paper also described the changes in the type of the collapse mechanism as the footing relative depth of embedment (D/B) and relative layer thickness (H/B) vary as functions of the strength ratio (c_u1/c_u2) of the two clay layers.