Face Stability Analysis of Tunnel (A case study: Karaj Subway Line 2)

Tunneling in complex geological and geotecnical conditions is often inevitable، especially in urban areas. The stability analysis and the assessment of ground surface settlement of a shield tunneling are of major importance in real shield tunneling projects. The objective of this research is to determine the collapse pressure of a shallow circular tunnel driven by a Tunnel Boring Machine (TBM) of the Earth Pressure Balance (EPB) type. In this study، analytical methods and three-dimensional numerical modeling with ABAQUS software were implemented to examine the effect of face pressure on the behavior of tunnel. The parameters were calculated using data from Karaj subway- line 2 in a case study. The analytical method used in this study is: Leca-Dormiex which is based on limit analysis stress. The method is based on a translational multiblock failure mechanism. Also، elastic and Mohr-Colomb constitutive model have been used for soil behavior. The results of analytical method and numerical modeling were then compared. According to the findings of this study، face pressure assessed from the analytical method of Leca-Dormiex (upper bound) is the minimum pressure that can be implemented on the face tunnel. Also، analysis shows that with implemention of suggested pressure of analytical method، Karaj subway face tunnel is most probably stable and consequently execution of pre-consolidation methods in this section of the tunnel does not seem to be necessary.