Reliability assessment of underground rock cavern limit states

Abstract

In this paper, four main cavern design criteria considered are: global stability, face stability, cavern deformation and bearing capacity of the rock reinforcements. The global factor of safety is used as the criterion for overall stability and computed by the shear strength reduction technique. In the contrast to overall stability, face stability is calculated through an iterative, closed-form equation proposed for open-face excavation. The critical strain value is set as the criterion for the serviceability limit state. The fourth design criterion adopted ensures that, at any given excavation stage, the loads on the rock bolts should be below the design capacity of the rock reinforcements. Numerical experiments are performed in order to identify the key influencing parameters for each design limit state and regression and Back Propagation Neural Network models are developed as the limit state functions. The First Order Reliability Method (FORM) was used to determine the probability of failure for the limit states. Through setting the factors of safety for global stability, face stability and the bearing capacity of rock reinforcements as the constraints to solve for the reliability index of serviceability limit state to meet the target performance level, the required minimum factor of safety values are obtained. This proposed approach enables a cost-effective analysis to be conducted for a rational design of underground rock caverns.