Experimental Study On Creep Mechanical Properties Of Thin Schist

Thin schist belongs to thinly laminated rock,which schistosity well developed and shows significant anisotropy.In this paper,we divide specimens into two groups which the loading directions are parallel and perpendicular to schistosity planes.Based on the regular uniaxial and triaxial loading tests,the uniaxial stress relaxation,uniaxial and triaxial creep tests are performed.Through stress relaxation test,which lasts 30 days at least for each specimen,it reflects apparent viscoelastic properties.And in uniaxial and triaxial creep test,which is carried out by step loading and lasts 42 days at most for single specimen,the creep properties and parameters are obtained in every loading test and it reveals that the creep behavior become apparent when loading direction is parallel to the specimen.The compressive strength and shear strength are compared to the parameters to the regular tests results,and the long term compressive strength is 60% of short term strength,which can reveal the influence of the direction of schistosity plane.And a new method is proposed to judge the long term strength by the trend of the inner elasticity modulus.The damage evolution equation is established based on the investigation of damage evolution and microscopic mechanism of creep behavior in each stage and put it into the Nishihara Model as a weakening factor.The damage based model can give a precise description of the mica-quartz schist.