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 (Kf) increased significantly with a decrease of subgrade stiffness, kv (or an increase of maximum foundation settlement, Smax). The measured values of Kf for the CWs placed on deformable ground may be greater than those for the at-rest (Ko) condition when Smax is greater than 3% of the total height of the wall (Ht). 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 Smax 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.