Abstract：Based on the mechanical behaviors of rock at the accelerating creep stage，a nonlinear coefficient of viscosity component is proposed. By using this proposed component，a new nonlinear visicoelasto-plastic creep model of rock is put forward；and the model can describe the three stages of rock nonlinear creep. Under certain condition，the model can be disintegrated into Burgers model or Nishihara model. The creep equation of rock at the constant stress is deduced；and the nonlinear creep properties of rock are studied in accordance with the proposed nonlinear creep constitutive model. Creep experiments are carried out for sandstone and marble specimens from left bank high slope of Jinping First Stage Hydropower Project by using the rock servo-controlled rheology testing machine；and the typical triaxial acceleration creep curves of rock are obtained. A new BFGS-LSM algorithm is brought forward by combining the quasi-Newton algorithm(BFGS) with the least square method(LSM). Throughout this algorithm，the exact solution can be fast approximated，which is not easily converged to the local minimum. The algorithm is adopted to investigate the triaxial creep tests of rock；and the related creep parameters of rock specimens using the proposed model are identified. The result shows that the new nonlinear viscoelasto- plastic creep model of rock accords better with the creep test curves.
