Time-Dependent Behavior of Jinping Deep Marble Taking into Account the Coupling Between Excavation Damage and High Pore Pressure

During the operation of the Jinping II hydropower station, the rocks surrounding the headrace tunnels have undergone failure because of the time-dependent creep effect that occurs due to the high geostress present and seepage. However, a few studies of the creep deformation of deep rocks have taken into account the coupling effect between excavation damage and pore pressure. This paper reports the results of a series of triaxial creep experiments conducted on Jinping deep marble in which the coupling between excavation damage and high pore pressure was studied. The results show that the magnitude of the creep deformation, the long-term strength, and failure mode of the excavation-damaged marble vary considerably with pore pressure. That is, the pore pressure has a significant effect on the marble. A new nonlinear viscoelastic-plastic damage (VEPD) model incorporating the effect of pore pressure was subsequently developed based on the experimental data. The values of the parameters appearing in the model were then obtained using a method of Universal Global Optimization. Good consistency is found between our theoretical predictions and test data which indicates that the VEPD model can be reliably used to simulate and predict the complete creep process in excavation-damaged deep rocks. It also gives a good account of the effect of pore pressure on the creep behavior. As a result, the model provides us with a better understanding of the long-term stability of underground engineering projects.