Reliability-based design of an anchor-support excavation

The design of the support of a 10m-deep urban excavation in Argentina is presented. A conventional approach was employed for the base case, where a set of geotechnical parameters is selected based on “engineering judgment” and a support system based on concrete wall and anchors was selected for the excavation. To enhance the understanding of the problem, a reliability-based analysis was performed using Plaxis: numerical models were employed to compute factors of safety and displacements for a range of input parameters and a First Order Second Moment (FOSM) technique was used to evaluate the probability of reaching a limit state. A Python code was developed to integrate FOSM into numerical analysis, resulting in an automatic calculation of the probability of failure using Plaxis. The probability of failure was estimated between 0.2% to 2% for the ultimate limit state and less than 0.8% for the serviceability limit state.