Safety evaluation of shallow tunnel based on elastoplastic-viscoplastic analysis

Application of an elastoplastic-viscoplastic constitutive model for tunnel safety evaluation is presented in this paper. For achieving this purpose, the model parameters were identied through FLAC code at rst for a section of Tehran Towheed tunnel by a back analysis process (as a case study). Next, with denition of two safety parameters related to short term (time-independent) and long term (time-dependent) behaviors, the safety of tunnel was assessed. For the short term behavior, which is related to excavation phase of tunnel, the elastoplastic part plays the essential role, so the safety parameter was dened based on hardening variable of constitutive model. But for the long term behavior, timedependent deformation will be generated during time, thus evaluation of safety was done by comparison of current shear strain and a dened 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 dened safety parameters on Towheed tunnel indicates that stability of tunnel is guaranteed during construction stages and long term situation.