Mechanical characteristics of sandstone containing arc prefa- bricated fissures

The natural rock mass is rich in similar arc-shaped crack defects,and the arc-shaped crack is prone to gen-erate new cracks under external load,and the growth of new cracks will easily lead to the instability of rock engineering structure. However,the mechanical characteristics of rock containing arc-shaped prefabricated frac-tures are not com-prehensively understood. Based on this,the arc-shaped fractures with different γ values (arc-shaped height and diame-ter ratio) were prefabricated in the sheet yellow-sandstone sample to study the me-chanical characteristics of sandstone containing arc-shaped prefabricated fractures. Using high pressure water jet cutting machine to cut arc-shaped fractures with different γ values in complete sheet yellow-sandstone samples,the effects of different arc-shaped fractures γ under uniaxial compression on peak strength,mean modulus and secession modulus,acoustic emission,failure process,initia-tion mode,initiation stress and failure mode of yellow-sandstone were studied by the YNS-2000 electro-hydraulic servo control test system,DS2 acoustic emission and digital photographic acquisition system. The complex function was used to solve the Riemann-Hilbert problem in the curved fracture stress field. The experimental results show that:① The bearing capacity of the sample after peak decreases gradually and the peak strength,average modulus and secant mod-ulus of the sample generally decrease with the increase of γ. The maximum peak intensity was 27. 09 MPa when γ = 0. 2 and the peak intensity was at least 18. 99 MPa when γ = 1. ② The inclination γ of arc crack has an important in-fluence on the initiation stress, initiation position, fracture evolution, acoustic emission characteristics and failure modes. The crack initiation stress of the test specimen decreases in general with the increase of the antithesis value. The average crack initiation stress of the test specimen was at least 4. 99 MPa when γ = 0. 8,and the average crack in-itiation stress of the sample was 11. 08 MPa with the maximum average crack initiation stress when γ = 0. ③ With the increase of γ,the failure mode of the sample changes from the mixed failure of tension and shear to the tensile failure. The sample is subjected to tension and shear failure when γ = 0. The specimen is tensile failure when γ is within the range of 0. 2-1. 0. The initial crack growth is not the cause of the ultimate failure of the sample,but the secondary crack growth and free surface penetration are the causes of the overall failure of the sample. The expression of the stress intensity factor was derived from the discussion of the crack propagation mechanism of the curved crack,and the corresponding value was obtained according to the expression. In this paper,only through uniaxial compression study, it is found that arc-shaped fracture has obvious influence on the mechanical parameters,fracture evolution process and failure mode of sandstone. In order to fully study the failure characteristics of sandstone containing arc-shaped fracture under external load,the mechanical characteristics of rocks containing such defects will be further studied by changing the loading form and loading path.