Reliability-Based Optimization Design for Drilled Shafts/ Slope System (DFI Student Paper Competition 2012)

Abstract In this paper, a reliability-based optimization design method is presented for design of a row of drilled shafts to stabilize an unstable slope while achieving the required target reliability index with minimum cost. In the previous developed deterministic analyses, the drilled shaft stabilization mechanisms for the reinforced slope were taken into account through the concept of soil arching, which was quantified by the load transfer factor in the limiting equilibrium analysis. However, due to the inherent uncertainties of the soil properties and the model error of the semi-empirical load transfer equation, a single value of factor of safety chosen in the deterministic approach may not yield the desired level of reliability. A modification of the deterministic method into a probabilistic method is developed in this paper. The monte carlo simulation (mcs) for the soil properties described by the log-normal distributions was employed to calculate the probability of failure (reliability index β) for the drilled shafts reinforced slope system. The developed theories are coded into a computer program (p-uaslope) for analyzing complex slope profile conditions. Finally, a case study (ohio ath-124 slope) is presented to illustrate the step by step design procedure using the developed probability approach..