Safety evaluation of shallow tunnel based on elastoplastic-viscoplastic analysis

Application of an elastoplastic-viscoplastic constitutive model for tunnel safetyevaluation is presented in this paper. for achieving this purpose, the model parameterswere identied through flac code at rst for a section of tehran towheed tunnel by a backanalysis process (as a case study). next, with denition of two safety parameters relatedto short term (time-independent) and long term (time-dependent) behaviors, the safety oftunnel was assessed. for the short term behavior, which is related to excavation phase oftunnel, the elastoplastic part plays the essential role, so the safety parameter was denedbased on hardening variable of constitutive model. but for the long term behavior, timedependentdeformation will be generated during time, thus evaluation of safety was done bycomparison of current shear strain and a dened limit shear strain based on experimentaldata. the results of back analysis showed a good capacity of model in reproduction oftunnel behavior. application of dened safety parameters on towheed tunnel indicatesthat stability of tunnel is guaranteed during construction stages and long term situation.