Interaction analysis of two collinear cracks with unequal length under the condition of unloading

It is common to have discontinuous cracks in the slope rock mass,whose extension and penetration induced by slope excavation and unloading are the main factors leading to landslide instability.To study the failure mechanism and interaction between cracks in a slope under unloading condition,based on the classical Kachanov method and superposition principle,the expression of stress intensity factor at the tip of a pair of unequal collinear cracks under the condition of unloading was derived.The stress intensity factor ratio F(the ratio of stress intensity factor at the tip of a crack in the presence of double cracks to that at the tip of a single crack) was defined,and the effects of crack inclination angle,spacing and length on the interaction between cracks were analyzed by the value of F.The biaxial unloading experiment of rock like materials was carried out,and the rocklike material was made up of 425 ordinary portland cement,standard sand and water according to the mass ratio of 1∶2.35∶0.5,and the experiment was carried out on MS500 triaxial impact rockburst test system.The results show that:① the dip angle of the crack has no effect on the interaction between the cracks;② when the crack spacing begins to be larger than the length of any crack,this crack has little effect on the propagation of the another crack;③ when the crack length is larger than the crack spacing,this crack begins to affect the propagation of another crack.When the crack length is less than the crack spacing,this crack has little effect on the propagation of another crack;and ④ axial initiation and peak load of specimens increase with the increase of crack spacing.The initiation angle and the initiation position are basically in agreement with theory and experiment,thus the feasibility and rationality of the theoretical calculation results are further verified.In this study,the effect of crack filling on the interaction between cracks is not considered,and it is limited to the interaction between two collinear cracks.The subsequent study will continue to explore the law of interaction between collinear three cracks and multiple cracks in the case of crack filling.