Nonlinear creep model of surrounding rock of long,large and deep tunnel

The rock excavation in the deep and long tunnels of Jinping second stage hydropower station(depth 2 525 m,length 19 km,width 13 m) showed an obvious deterioration to its rheological properties.The CSS-283 bi-direction universal servo testing machine is used to conduct uniaxial compression creep test and shear creep test for the surrounding rock(soft slate).The respective rheological model of rock for shear and uniaxial compression creep processes is established by introducing the rheological parameters which are functions of hardening and time.This nonlinear creep model presents the expression of strain equation,which is a together of four individual strain parts,including the instantaneous elastic deformation,viscoelastic deformation,instantaneous plastic deformation and viscoplastic deformation.What's more,those parameters in the strain equation are non-stationary,they are correlated with time and stress.Besides,the harding characteristic of rock samples is also considered during the behaviors of their creep process.Based on that the corresponding three-dimension model is therefore developed,the theoretical calculated results are well consistent with the test results.Finally,numerical simulation is performed to study the excavation of deep tunnels of Jinping hydropower station and the tunnel deformation after the 190 days' excavation is also obtained.Accordingly,these investigation results can provide a theoretical guidance for the engineering construction.