Study On The Failure Mode Of Horseshoe-shaped Cavity With Adjacent Cracks Under Compression

Rock mechanical properties and failure modes are the focus of rock research.Natural rock has various forms of defects such as natural cracks and small cavities.The existence of these defects will affect the mechanical properties and failure modes of the rock.Therefore,it is very important to study the impact of different defects on the rock failure mode.This paper mainly researches the failure modes of rock cavity with adjacent cracks under compression.In this study,we combined laboratory test,numerical analysis,and theoretical analysis to study the failure modes of horseshoe-shaped cavities with adjacent cracks.We use test specimens to carry out this test.And the cavity shape is horseshoe-shaped,the natural cracks are simulated by adjacent cracks preset in the test specimens,and the adjacent cracks including single cracks and cross cracks.The study parameters of the single cracks are the length of the crack and the distance between the crack and the cavity;the study parameters of the cross cracks are the length of the secondary crack and the angle between the secondary cracks and the maximum principal stress.The specimens under the two conditions are loaded in two loading modes:uniaxial loading modes and biaxial loading modes.The test results show that the adjacent cracks have a great impact on the failure mode of the underground cavities.Different crack forms and different crack parameters make the cavities produce different failure modes.According to the test results,the following main conclusions can be drawn.When there are adjacent cracks around the cavities,the expansion fractures will first be generated from the vault around the cavity,rather than from the crack tip of the adjacent cracks.Compared with the uniaxial loading mode,the expansion fractures of the specimens under the biaxial loading mode are more easily attracted by the adjacent cracks.When the adjacent crack mode is a single crack and the length of the adjacent crack is the same,the smaller the distance between the single crack and the cavity,the stronger the attraction ability of the single crack tip to the expansion fractures;When the distance between the single crack and the cavity is the same,the longer the single crack length,the stronger the single crack's ability to attract the fractures.When the adjacent crack is cross cracks,and the angle between the secondary crack and the maximum principal stress is small,in this paper,a=0°,the cavity vault only generates one expansion fracture,and the expansion fracture easily expands to the secondary crack along the maximum principal stress;When the angle between the secondary crack and the maximum principal stress is large,in this paper,a=450 and 90°,the cavity arch is prone to generate two expansion fractures.And when a=45°,the attracting capacity of the primary and secondary cracks is similar and expands.The fractures propagate towards the primary crack and secondary crack at the same time.In the case with a single crack and in the case with cross cracks with a=0°,the failure mode of the rock of the cavity is shear failure;in the case with cross cracks,when a=450 and 90°,the failure mode of the rock is prone to produce cutting body.