Viscoelastic-plastic creep solutions and deformation properties of tunnels in swelling rocks under seepage

With the effects of many parameters, such as seepage, swelling and dilatation, the deformation of tunnels in swelling rocks under seepage is a complex time-dependent problem. The closed strain hypothesis is proposed. The equilibrium equation for the tunnels in swelling rocks under seepage is established. And then the elastoplastic solutions considering the effect of dilatancy angle are obtained. The answers of Yu dongming's and Hou gongyu's are the two special cases of the solutions. Accordingly, the viscoelastic-plastic creep solutions of the tunnels in swelling rocks under seepage considering the effect of swelling strain are obtained by using the modified Nishihara model. The influence of the related parameters on the time-dependent deformation of tunnel wall is analyzed, such as inflation, seepage and expansion. The results show that the time-dependent deformation presents viscoelastic-plasticity gradually with the decrease of the ratio of inner to outer water heads or the increase of the dilatancy angle. The moisture expansion coefficient α₂ affects only the viscoelastic deformation of the surrounding rock, and the displacement monotonically linearly increases with it. At the early stage of excavation, the closed strain develops rapidly into displacement, which greatly influences the deformation of swelling rocks under seepage. The results can be taken as a guide for the construction and deformation control of the tunnels in swelling rocks.