Investigation of Creep Behaviors of Wudang Mica Schist by Triaxial Compression Tests

Triaxial compression creep tests were conducted on Wudang mica schist samples to clarify the creep anisotropy characteristics. The mica schist samples were divided into parallel group and vertical group according to the angle of axial loading and schistosity plane. The creep tests were set up with step function loading under varied confining pressure conditions. The test results show that mica schist creep have 4 stages: instantaneous deformation stage, decay creep stage, steady creep stage and accelerating creep stage. The deformation is dominated by instantaneous deformation at low levels of stress. Then the creep value continued to increase as the stress grew. In comparison with the vertical group under same confining pressure and similar axial loads, the parallel group presented large instantaneous strain increments and axial creep value, high creep speed and short decay creep time. Experimental results showed that the vertical group was finally destructed in the form of shear fracture and the parallel group was finally destructed in the form of cleavage fracture, which indicated distinct creep anisotropy. A modified burgers creep model was introduced to describe mica schist’s creep characteristics and identify the creep parameters, and the result was proved to be efficient in description of mica schist’s creep features by the fitting results.