Reliability-Based Design for Slope Stabilization Using Drilled Shafts

In this paper, a reliability-based computational algorithm was developed and coded into a computer program, P- UASLOPE, for design of a row of equally spaced drilled shafts to achieve target reliability index for the drilled shafts reinforced slope system. The Monte Carlo simulation technique was used in the previously developed deterministic computational program, in which the limiting equilibrium method of slices was modified to incorporate the arching effects of the drilled shafts in a slope. Uncertainties of soil parameters for each soil layer in the slope were considered by statistical descriptors, including mean, COV, and distribution function. Model errors involving the semi-empirical predictive equation for the load transfer factor for characterizing the soil arching effects were considered by statistics of bias. A total of 41 cases of 3-D finite element simulation results were used to determine the statistics of bias. A design example was given to demonstrate the use of P-UASLOPE program for optimized design of a drilled shafts reinforced slope system for achieving the most economic combination of design variables (i.e., location, spacing, diameter, and length of drilled shafts) while satisfying the design requirements in terms of target reliability index of the drilled shafts/slope system and the structural performance of the drilled shafts. Sensitivity analysis of the influence of bias of model errors on the computed probability of failure for the design example indicates the need for more cases of 3-D finite element simulation results for obtaining a more accurate semi-empirical predictive equation for the load transfer factor.