Safety evaluation of shallow tunnel based on elastoplastic-viscoplastic analysis


Department of Civil Engineering, Bu-Ali Sina University, Hamedan, Iran


Application of an elastoplastic-viscoplastic constitutive model for tunnel safety evaluation is presented in this paper. For achieving this purpose, in the first step, through FLAC code, the model parameters were identified for a section of Tehran Towheed tunnel (as a case study) by a back analysis process. In the second step, with definition of two safety parameters related to short term (time-independent) and long term (time-dependent) behaviors, the safety of tunnel was assessed. For short term behavior which is related to excavation phase of tunnel, the elastoplastic part plays the essential role, so the safety parameter was defined based on hardening variable of constitutive model. But for long term behavior, time-dependent deformation will be generated during time, thus evaluation of safety was done by comparison of current shear strain and a defined limit shear strain based on experimental data. The results of back analysis showed a good capacity of model in reproduction of tunnel behavior. Application of defined safety parameters on Towheed tunnel indicates that stability of tunnel is guaranteed during construction stages and long term situation.