# Study of Geotechnical Parameters Uncertainties in Analysis of New Tunnel Construction Over the Existing Tunnel

Document Type : Research Article

Authors

1 Department of Geotechnical Engineering, Faculty of Civil Engineering, University of Tabriz

2 Department of Geotechnical Engineering, Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran

3 Department of Water Engineering , Faculty of civil Engineering, University of Tabriz

Abstract

This paper aims to study the problem of a new tunnel construction over – crossing the existing tunnel through the probabilistic point of view. Metro line-7 tunnel above-crossing line-6 tunnel in Tehran was chosen as a case study project. The numerical modeling of the problem was carried out by the FLAC3D software. The parameters of the cohesion and the friction angle of the third layer as well as the surcharge on the ground level were assumed as random variables. Generating the random numbers and fitting the probabilistic distributions to these variables was carried out by the Monte – Carlo method. The displacements at four points of the existing tunnel (line 6) were recorded due to new tunneling, and the appropriate probabilistic distribution was fitted based on the mean, median and skewness of each set of random numbers. According to these probabilistic distributions, the probability of the displacements more or less than a specific displacement can be determined. The results indicate that although input parameters have normal distributions, not all of the outputs have symmetric or normal distributions, and the results of the deterministic method are not the same as the mean values of stochastic approach. As well, the probability of displacements greater than the mean value at the bottom and right side of the existing tunnel is 56 % and 55/5 %, respectively.

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