STUDY ON CONSTITUTIVE MODEL OF HARD ROCK CONSIDERING SURROUNDING ROCK DETERIORATION UNDER HIGH GEOSTRESSES

In the practice of tunneling in hard rock stratum under high geostress,mostly,two phenomena can be observed:(1) the rock has the activity of brittle breakage induced by the unloading;and(2) the parameters of surrounding rock in the excavation damage zone(EDZ) have changed,including elastic modulus E,cohesion c and friction angle φ.Therefore,a rock mass deterioration model(RDM) is presented.The RDM takes the damage of rock as a process of propagation of microcracks.It means that the microcracks lead to the reduction in deformation modulus and cohesion and the increase of friction angle in the EDZ.The relationship between mechanical parameters and damage degree represented by general plastic strain of EDZ is established.Then,the model defines an equation which is the function of general plastic strain to rule the change trend of parameters.It is implemented by integrating with the FLAC3D.The model has three basic characters,i.e.the stress-strain curve is composed of linear elastic part,stress falling part and plastic flow part;the subsequent yield surface can change its shape and area along with accumulation of general plastic strain;and the mechanical parameters are updated with the deteriorating of surrounding rock in EDZ.This model is verified by fitting stress-strain curve of granite in triaxial compression test and modeling experimental tunnel at Jinping II Hydropower Station in China.The results indicated that the RDM is reasonable.