Various types of numerical analyses such as the finite element method, the boundary element method and thedistinct element method, are used in rock mechanics and in engineering practices for designing rock structuressuch as tunnels, underground caverns, slopes, dam foun
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Various types of numerical analyses such as the finite element method, the boundary element method and thedistinct element method, are used in rock mechanics and in engineering practices for designing rock structuressuch as tunnels, underground caverns, slopes, dam foundations and so on. In this paper, the results of backanalysis of Koohin tunnel which is located in the first section of Qazvin – Rasht railway have been presented.The main purpose of this paper is to perform the back analysis of the mentioned!tunnel with the use of numericalmodels. For modeling the tunnel, two different sections are analyzed with Flac 2-D software, which are 30+150and 30+900. To perform back analysis the suitable interval of geomechanical parameters according to the testswhich performed on the core drillings has been determined. With the use of Direct Method in back analysis, theerrors of models have been corrected in several steps and finally the geomechanical parameters of control in30+150 station (Elastic Modules = 0.3 GPa, Cohesion = 0.21 MPa & Internal Angle of Friction = 34°) and in30+900 station (Elastic Modules = 0.3 GPa, Cohesion = 0.21 MPa & Internal Angle of Friction = 35°) have beenachieved. The geomechanical parameters which achieved from back analysis are completely in the choseninterval and compliance with the results of tests which performed on core drillings. On this basis and accordingto the match of the geomechanical parameters which obtained from back analysis with the parameters whichused in designing of the tunnel, the tunnel design and the structure method were confirmed.
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