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Abstract Taking green sandstone samples from the diversion tunnel of Jinping II hydropower station as research objective，the unloading triaxial rheological tests by keeping axial stress and unloading lateral stress by steps are performed in laboratory. According to experimental results，the creep laws of axial and lateral deformations under unloading stress path are studied. Development of lateral plastic deformation is more rapid than that of the axial direction；and the response to failure in lateral direction is more obvious than that in axial direction. After detailed research and analysis of the test results，and considering damage effects of rock parameters，the damage evolution equation and nonlinear rheological Burgers model with various parameters are proposed. In the model，the creep parameters of sandstone are weakened with viscous strain gradually，so the deterioration process of the material can be reflected by unsteady creep parameters directly. By taking the sum square of survival difference as optimization objective，the least square embedded in Levenberg-Marquardt(LM) algorithm is adopted to optimize the fitting parameters of models. And then，nonlinear damage rheological constitutive model is established. By comparing with the test data，the fitting curves are well fitted with test data curves；it is shown that the rheological model can preferably present attenuating creep and steady rheological characteristics of Jinping green sandstone.
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Received: 05 August 2009
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