Three-Dimensional Active Earth Pressures for Unsaturated Backfills with Cracks Considering Steady Seepage

Abstract

Traditional analyses for active earth pressures considered soils dry or saturated by the application of a two-dimensional (2D) failure pattern. However, soils are usually unsaturated in nature, and the collapse of backfills presents a three-dimensional (3D) characteristic. The extant studies proved that the existence of cracks and seepage flow encountered in backfills would impact active earth pressures but are still limited to 2D conditions. To this end, this study developed an analytical framework to evaluate the 3D active earth pressure considering the presence of cracks and steady-infiltration effects within unsaturated backfills. Based on the kinematic approach of limit analysis, a suction-induced effective method is introduced into a 3D failure mechanism to characterize the collapse of unsaturated backfills. By means of the work rate balance equation, the most adverse location of cracks and the explicit expression of active thrust under steady seepage conditions can be obtained through the incorporation of the suction stress profile. The presented method is verified by comparison with the exact cases in previous studies and comparison with the results of numerical simulation. A systematic parametric study is conducted to reveal the impacts of width-to-height ratio, air-entry value, pore-size distribution, vertical discharge, and cracks on the active earth pressure variations. The results show that considering 3D effects is significant because it leads to a lower economic cost for the design of retaining walls; the presence of cracks and the effect of steady infiltration encountered in unsaturated backfills would increase the lateral force of earthen structures. This study presented a more realistic understanding of the service state behavior of retaining walls and a useful strategy for evaluating the 3D active earth pressure.