岩石节理峰前循环直剪试验颗粒流宏细观分析

利用二维颗粒流(PFC2D)程序较为完善地实现了考虑二阶起伏体岩石节理的峰前循环数值直剪试验,并分别从宏观和细观角度分析了节理峰前循环直剪试验中节理累积损伤特征与抗剪强度的变化规律。对比分析已有的室内试验成果,验证了计算方法的可靠性。研究表明:①随着岩石节理一阶起伏角、法向压力的增大,节理的破坏模式按爬坡—爬坡啃断—啃断趋势发展,且抗剪强度随着一阶起伏角、法向压力的增大总体上呈增大趋势。②低幅值的循环荷载对节理剪切强度的影响极为有限,甚至可以忽略,但随着循环加载幅值的增加,节理起伏体上裂纹的扩展贯通程度、裂纹的数量均显著增多,表明循环加载幅值的大小是决定节理起伏体累积损伤速度的关键因素。③节理裂纹数量随循环加载次数的增大而增加,且有增速的趋势,在循环加载次数增加到某个量级时,裂纹出现激增的现象,表明节理疲劳裂纹的扩展贯通有累积后突变的演变特征;不同破坏模式下,节理的峰值抗剪强度均随着循环加载次数的增加呈现出先增后减的变化趋势,表明有限次数的循环加载有利于增大节理的峰值抗剪强度,但循环加载最终会因节理的累积损伤造成其抗剪强度的劣化。研究结果丰富了室内试验成果,有助于进一步认识岩石节理在微震频发作用下的累积损伤与强度劣化规律。

Macroscopic and microscopic analysis of particle flow in pre-peak cyclic direct shear test of rock joint

The pre peak cyclic numerical direct shear test of rock joints considering second order asperity was implemented using two dimensional granular flow (PFC2D) program.The cumulative damage characteristics of rock joints and variation law of shear strength were respectively analyzed from the macroscopic and mesoscopic view.The reliability of the calculation method was verified by comparing and analyzing the existing laboratory test results.The results are as follows:① as the first order asperity or the normal stress increases,the failure mode of the rock joint has the tendency to change from climbing to climbing cutting to cutting,and the shear strength of rock joint shows the trend to increase generally.② The effect of low rising value of cyclic loading on the joint shear strength is extremely limited and can be neglected,while the propagation and interpenetration extent and number of cracks in the rock asperities are largely increased as the value of cyclic loading increases,which indicates that the value of cyclic loading is an important factor determining the rate of cumulative damage.③ As the pre peak cyclic loading times increases,the number of cracks in the rock sample increases and so does the increase rate of it,and the surge phenomenon of cracks occurs when the number of cyclic loading increases to a certain level,showing that the propagation and interpenetration of cracks have the characteristic of mutation after accumulating.As the cyclic loading times increase,the peak value of the joint shear strength has the variation trend of increasing firstly and decreasing latterly,which shows that the limited number of cyclic loading is beneficial to increase the peak shear strength of joints,but the cyclic loading will eventually cause the degradation of shear strength due to the accumulation of joint damage.This study enriches the indoor test results and helps to further understand the accumulated damage and strength deterioration rule of rock joints under the action of frequent microseisms.