Experimental Study On Shear Mechanical Properties Of Rock Joints Under The Pre-peak Cyclic Shear Loading And Unloading

Cyclic shearing at low stress levels caused by microseism,engineering blasting and so on has an important influence on the instability and failure of jointed rock mass engineering.In order to study the shear mechanical characteristics of rock joints under pre-peak cyclic shearing,the RDS-200 rock shear test system was used to carry out direct shear tests on artificial splitting yellow sandstone joints under the pre-peak cyclic shearing condition.Compared with the shear mechanical characteristics of rock joint without pre-peak cyclic shearing,the influences of pre-peak cyclic shear on the pre-peak shear stiffness,peak shear strength,peak shear displacement and residual shear strength are obtained.The results show that: after pre-peak cyclic shearing,the pre-peak shear stiffness of rock joints increases when the normal stress is 2 MPa;but when the normal stress is 4～10 MPa,the pre-peak shear stiffness of rock joint within the cyclic shear stress amplitude increases,and the pre-peak shear stiffness of rock joint beyond the cyclic shear stress amplitude decreases.After pre-peak cyclic shearing,the peak shear strength decreases by 10%～20%,and the decrease percentage increases logarithmically with the increase of normal stress.The peak shear displacement increases by 2%～40%,and the increase percentage decreases as a logarithmic function with the increase of normal stress.After pre-peak cyclic shearing,the residual shear strength of rock joint doesn’t have a significant change,the difference between peak shear strength and residual shear strength decreases,and the loss percentage of work done by the post-peak shear stress also decreases.Acoustic emission signal acquisition was carried out at the same time of shearing test.By analyzing the variation of acoustic emission signal characteristics during shearing,the results showed : In terms of cumulative AE counts curve and cumulative AE energy curve,the no-cycle group and the pre-peak cycle group samples have different curve types,the difference is mainly reflected in the cycle stage.After the pre-peak cyclic shear loading and unloading,the pre-peak cumulative acoustic emission counts and energy of the samples in the pre-peak cyclic group is generally greater than that of the samples in the no-cycle group,and it shows a decreasing trend as the normal stress decreases.The research results provide certain reference for the stability evaluation of jointed rock mass under low stress cyclic loading,and have practical significance for rock engineering construction and disaster prevention.73 pictures,12 tables,85 references.