Behavior of soil retaining walls on deformable foundations

Cost-effectiveness evaluations for soil retaining structures require better knowledge of the integrity and serviceability of these structures subjected to foundation settlements. As a preliminary study on the performance-based design of soil retaining structures that takes into account the influence of foundation settlements, the settlement-tolerating characteristics of cantilever soil retaining walls (CWs) placed on deformable foundations were explored using a 0.6 m-high model cantilever wall backfilled with rhombically stacked 1.96 mm uniform diameter steel rods used as two-dimensional backfills of the wall. Screw jacks were used to simulate a non-yielding foundation and three types of spring with various spring constants were used to simulate deformable foundations with maximum foundation settlements of approximately 2%, 5%, and 9% of the total wall height. It was found that the measured values of the lateral pressure coefficient (K_f) increased significantly with a decrease of subgrade stiffness, k_v (or an increase of maximum foundation settlement, S_max). The measured values of K_f for the CWs placed on deformable ground may be greater than those for the at-rest (K_o) condition when S_max is greater than 3% of the total height of the wall (H_t). For the tested cantilever wall with moderately high safety factors against sliding and overturning based on a commonly adopted assumption of an unyielding foundation, significant decreases in safety factors associated with the increase in S_max were observed. Equations for additional margins of design lateral pressure coefficient and/or safety factors against sliding and overturning for the wall, expressed as a function of maximum foundation settlement, are proposed to substantiate the safety evaluation of soil retaining walls situated on a deformable foundation.