Probability of failure determination for tunnels in rock by using Monte Carlo simulation

Convergence - confinement method can be used to analyze rock support systems in interaction with rock mass in order to select the appropriate supports system for tunnels in rock. This method enables calculation of the charge applied to the support system and the factor of safety for the tunnel supports. The factor of safety calculated from traditional deterministic analysis methods cannot fully represent tunnel stability. There are many uncertainties in parameters used to calculate the factor of safety, and these uncertainties are not integrated in a deterministic analysis, but can be taken into account using a reliability analysis. Reliability analyses, used to calculate probability of failure for tunnel support system, is a complement of the factor of safety calculated by using deterministic analyses. In this paper, Monte Carlo Simulation is used to calculate probability of failure for tunnel support system. This article shows that significant error may be introduced by accepting a distribution for the performance function, which is obligatory for methods like FOSM, FORM, PEM. It is concluded that in cases when the distribution for the performance factor is not fully known, Monte Carlo analysis may give better results.