Comparison of empirical and numerical methods in tunnel stability analysis

Abstract

The stability of a tunnel can be evaluated using mathematical solutions, empirical methods, or numerical modelling. Mathematical solutions are precise methods; however the need to conduct mathematical calculations usually decreases the user's desire to use this method. Empirical methods are based on the experience gathered by researchers in various parts of the world whereas numerical modelling utilises computing power and, using various modelling techniques, can be a precise way of solving very complex problems. In this method the environment and the geometry can be set by the user. This method allows the user to conduct sensitivity analysis. In this article, empirical methods and numerical modelling using UDEC software were used to conduct a stability analysis of the access tunnel at the Shahriar dam crest, which was one of the most important tunnels of this project. In addition, numerical modelling was used to predict the stresses and deformations around the perimeter of the tunnel, and select the most suitable ground support system. The results obtained from both methods were compared for selection of the best suited support system. The results indicated that the empirical methods presented similar results to the results of numerical modelling at the first stages of tunnel design in jointed rocks. Therefore, in the absence of sufficient information for numerical analysis, the results of the empirical method can be used for this project.