Based on a triaxial creep test of saturated phyllite, a time-dependent variation law of creep characteristics of saturated phyllite under the coupling effect of pore water pressure and unloading stress was investigated. The results show that the creep failure of saturated phyllite is a typical brittle failure, characterized by instantaneous application of a force. An increase in unloading stress and pore water pressure can accelerate the creep failure of saturated phyllite. The Burgers model was improved by adopting a variable of instantaneous failure, and an elasto-plastic damage body was established by introducing a variable of time-dependent damage. With the improved Burgers model in serial connection with the elasto-plastic damage body, a three-dimensional damage constitutive model for rock creep was proposed in consideration of the coupling effect of excavation unloading and pore water pressure. After regression analysis and parameter identification with the Levenberg-Marquardt (L-M) algorithm for the test results, it is found that the theoretical stress-strain curve from the proposed model are in good coincidence (R²>0.9) with the practical ones for decay, steady-state and acceleration phases of saturated phyllite from the experiments, verifying the accuracy of the model. It is concluded that this model can effectively describe the creep behaviour of mine slope mass under the long-term coupling effect of excavation unloading and pore water pressure.

open-pit slope  /  phyllite  /  triaxial compression test  /  creep test  /  constitutive model  /  Burgers model  /  damage variable  /  elasto-plastic body  /  pore water pressure  /  excavation unloading