Ultimate Limit State Reliability-Based Optimization of MSE Wall Considering External Stability

Abstract

We present reliability-based optimization (RBO) of the Mechanically Stability Earth (MSE) walls, using constrained optimization, considering the external stability, under ultimate limit state conditions of sliding, eccentricity, and bearing capacity. The design is optimized for a target reliability index of 3 that corresponds to an approximate failure probability of 1 in 1000. Reliability index is calculated by the first-order reliability method (FORM). The MSE wall, founded on cohesionless soil, with horizontal backfill and uniform live traffic surcharge, is studied. The RBO results are reported for the height of MSE wall ranging from 1.5 m to 20 m. For target reliability index of 3, the optimized length to height ratio, Lopt/H, of the MSE wall is greater than 0.7 (the minimum length to height ratio requirement of AASHTO) for H≤4.5 m, and then it decreases below the minimum required value of 0.7 for H>4.5 m. The RBO approach presented in this study will help practitioners to achieve cost-effectiveness in design.