Assessment of Geotechnical Parameters Uncertainties in Analysis of New Tunnel Construction influence on the Existing Tunnel at their Non-Level Intersection

Various uncertainties exist in the engineering problems, so it is necessary to study these problems from probabilistic point of view. This paper aims to evaluate the interactions between new tunnel over – crossing the underlying existing tunnel. Metro line-6 tunnel above-crossing line-7 tunnel in Tehran was chosen as a case study project. In this study the numerical investigation was performed using the FLAC3D software and cohesion and friction angle of third layer and the surcharge on the ground level were assumed as random variables. Generating the random numbers and fitting the probabilistic distributions to the geotechnical variables was done using the Monte – Carlo method. The displacements at four points of existing tunnel (line 7) were recorded due to new tunneling and the appropriate probabilistic distribution was fitted according to the mean, median and skewness of each set of random numbers. According to these probabilistic distributions the probability of occurrence of the displacements more or less than a specific displacement can be determined. The results indicated that although input parameters have normal distributions, not all the outputs have symmetric or normal distributions and the results of deterministic method aren’t as the same of mean values of stochastic approach. For all random parameters the probability of displacements greater than the mean value at the bottom and right side of the existing tunnel due to the new tunneling is 56 % and 55/5 %, respectively.