Confidence level-based robust design of cantilever retaining walls in sand

Reliability-based geotechnical design entails accurate sample statistics (i.e., mean and standard deviation or coefficient of variation, denoted herein as cov) of soil parameters. However, the cov values of soil parameters are difficult to determine with confidence due to the limited availability of high-quality data and inherent spatial variability. As a result, estimated cov values of soil parameters can vary within a wide range, which can result in overdesign or underdesign. In this paper, a confidence level (CL)-based method is proposed to address the problem of geotechnical design in the face of uncertainty. Here, CL is a measure of confidence that the target reliability index will be satisfied in the face of uncertainty in the estimated cov. The proposed method is demonstrated through the design of a cantilever retaining wall in sand. To ensure the practicality of the proposed method, a simplified approach was developed, which requires little extra effort over that required for traditional reliability-based design. To develop the CL-based method further, a metric called the “true reliability index” is proposed, which is the actual reliability index in the face of the uncertainty in the estimated parameter statistics (mainly cov).