Probabilistic stability analysis of Naien water transporting tunnel and selection of support system using TOPSIS approach

Tunnel stability analysis is a geotechnical engineering problem characterized by many sources of uncertainty. In such cases, rock and soil characteristics could not be defined by deterministic values and probabilistic technique would be as a suitable alternative. Naien water transporting tunnel is a circular tunnel with 6 m in diameter which is being excavated in such conditions and it is almost impossible to analyze the tunnel stability deterministically. To use probabilistic analysis, the best fitted distributions to rock mass characteristics were first obtained. Using Monte-Carlo simulation method and considering four support systems, the distribution of factor of safety was obtained for each support system. To select the best support system, TOPSIS multi-attribute decision-making method was used by considering five criteria for each support system ( as alternatives) including: probability of failure (using probabilistic method), factor of safety (using deterministic method), maximum displacement, cost and factor of applicability. The results of this research emphasize that the deterministic or probabilistic alternatives could not be separated by such comprehensive technique for stability analysis and should be interpreted together. At last, using such TOPSIS application associated with stability analysis techniques can assist the engineers to effectively evaluate the support system alternatives for a tunneling project.