The four seepage tunnels in Jinping II Hydropower Station are buried in the hard brittle rockmass. The complex geological condition including high stress induced by great depth and high seepage pressure will bring about many engineering problems

especially the long term stability problem. In order to reflect the character of the visco-plastic deformation

the combinative models of cohesion weakening-friction strengthening model and the visco-elastic model are introduced in this study. And based on the in-situ displacement monitoring data

the visco-elasto-plastic model and its parameters are obtained by the intelligent method based on GP and PSO methods. The rheological mechanic characters of the surrounding rockmass in the seepage tunnels are simulated by using FLAC3D. At the same time

this program can also simulate the mechanism between the sprayed concrete

rock bolts and rockmass and the coupling effect of fluid and solid under the high seepage pressures on the structures. Through the analysis of the calculated results

the long term stability of the tunnels is estimated by using the integrating method of multi-index including displacement

displacement velocity

stress

failure approach index and the internal force in the support structures and soon. The results are of importance to the design and construction of this project.