Assessing expected benefit of site investigation program for reliability-based design of slope

The site investigation (SI) is important to reduce the uncertainty of the slope soil properties. Its effectiveness is highly related to the planning of an SI program such as borehole layout. It is thus tempting to assess the potential uncertainty reduction of an SI program. This paper presents a method to assess the expected benefit (EB) of an SI program for slope. The cost saving of reliability-based design under unknown observations is considered. Compared with the previous methods, this method can take into consideration the uncertainty of the scale of fluctuation (SOF) of the soil, and the knowledge about the consequence of slope failure is not required. A subset logistic regression method is suggested to approximate the probability of slope failure. The SI program can be optimized by selecting the borehole layout with the maximal EB. For the example in this paper, it is found that the EB of an SI program depends on the SOF of the soil. If the uncertainty in the SOF is not considered, the EB may be underestimated or overestimated. The proposed method provides a practical and efficient way to assess the effectiveness of SI program for design of slopes. •A reliability-based method to assess site investigation program is proposed.•The uncertainty of scale of fluctuation is systematically considered.•A method of subset logistic regression is developed to check the feasible design.•The site investigation program can be optimized by maximizing the expected benefit.