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| Cyclic shear mechanical properties of 3D rough joint surfaces under constant normal stiffness(CNS) boundary conditions |
| LIU Richeng1,2,YIN Qian1,2,YANG Hanqing1,JING Hongwen1,JIANG Yujing2,YU Liyuan1#br# |
| (1. State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology,Xuzhou,Jiangsu 221116,China;2. Faculty of Engineering,Nagasaki University,Nagasaki 852–8521,Japan) |
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Abstract In this study,the effects of the normal stiffness(0–7 GPa/m) and the number of cyclic shearing(1–10) on the shear stress,normal deformation,normal stress,shear stress path,surface resistance index,acoustic emission responses and surface wear characteristics of joint surfaces were revealed through conducting cyclic shear tests on 3D rough joint surfaces under constant normal stiffness(CNS) boundary conditions. The experimental results indicate that the shear stress-shear displacement path exhibits typical normal stiffness-dependent characteristics. When the normal stiffness is small,the shear stress declines gradually after the initial peak value,showing a stress softening behavior. With increasing the normal stiffness,the increase extent of the normal displacement declines gradually,while the increase extents of both shear-induced shear stress and normal stress present a gradual increase,characterized by a stress hardening behavior. When the number of cyclic shearing is 1,with an increase of the normal stiffness from 3 GPa/m to 7 GPa/m,the apparent cohesion and apparent internal friction angle of the joint surfaces increase by 22.40% and 26.84%,respectively,while the surface resistance index remains generally stable. With continuous increasing the number of cyclic shearing,the initial peak shear stress declines gradually,while the decrease extent becomes slow down and gradually stabilizes. Especially,the decrease extent of the initial peak shear stress experiences the largest reduction(24.93%–60.91%) with increasing the number of cyclic shearing from 1 to 2. During the cyclic shear process,due to cutting and wearing of the asperities,the joint surfaces tend to be smooth,resulting in gradual reduction of the increase extents of both the dilatancy deformation and the normal stress. When the shear displacement is larger,compared with the normal stress,the attenuation of the increase extent of the shear stress is more sensitive and the surface resistance index increases gradually. The cumulative acoustic emission energy declines with the number of cyclic shearing. However,while the normal stiffness increases from 0.5 GPa/m to 7 GPa/m,the cumulative acoustic emission energy in the stable stage shows an increase by a factor of 2.298,and the ratio of the shear area increases by 72.02%–97.11%.
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