峰前循环剪切作用下岩石节理剪切力学特性

Shear mechanical properties of rock joints under pre-peak cyclic shearing condition

微震、工程爆破等低应力循环剪切荷载作用对节理岩体工程失稳破坏具有重要影响。为研究峰前循环剪切加卸载作用下岩石节理剪切力学特性,采用RDS-200型岩石节理剪切试验系统对人工劈裂黄砂岩节理进行了峰前循环剪切下的直剪试验。通过与未进行峰前循环剪切加卸载时岩石节理力学参数预测值对比,得到峰前循环剪切加卸载作用对峰前剪切刚度、峰值剪切强度、峰值剪切位移与残余剪切强度的影响。结果表明:(1)峰前循环剪切加卸载后,当法向应力为2MPa时,岩石节理峰前剪切刚度增大,当法向应力为4~10MPa时,岩石节理峰前剪切刚度在循环剪切应力幅值范围内增大,在超出循环剪切应力幅值时减小;(2)峰前循环剪切加卸载后,峰值剪切强度降低了10%~20%,降低百分比随法向应力增大整体呈对数函数增大;峰值剪切位移增加了2%~40%,增加百分比随法向应力增大整体呈对数函数减小;(3)峰前循环剪切加卸载后,岩石节理残余剪切强度无明显变化,峰值剪切强度与残余剪切强度差值减小,峰后剪切应力做功损失百分比降低。

Cyclic shearing at low stress levels caused by microseism, engineering blasting 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:(1) 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.(2) 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.(3) 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.