大尺寸岩石在低频周期扰动载荷下的力学特性试验研究

Testing study on mechanical properties of large-size rock under low-frequency periodic disturbance load

岩石长期处于高静应力状态且频繁受到周期扰动载荷的影响是引发各种地质灾害的关键因素。利用自制的CX-8568冲击扰动围岩试验系统对大尺寸红砂岩开展了低频周期扰动载荷下的力学特性试验,分析了高应力状态下不同扰动平均应力、不同扰动载荷幅值下岩石的应变、损伤变量的演化规律。结果表明:岩石在周期扰动载荷下的破坏存在门槛值,其载荷低于门槛值时岩石不会发生破坏,岩石弹性模量存在强化现象;高扰动平均应力、高扰动载荷幅值均为岩石破坏的不利因素;当扰动上限应力超过岩石单轴抗压强度后,扰动平均应力和扰动载荷幅值的增大对岩石破坏时的循环次数影响愈发显著;当扰动上限应力相同,但扰动平均应力和扰动载荷幅值不同时,岩石破坏对扰动平均应力的敏感度高于扰动载荷幅值;周期扰动载荷下岩石破坏较静态加载更剧烈;随着扰动平均应力或扰动载荷幅值的提高,岩石破坏形态由以拉剪破坏为主导过渡至以拉伸劈裂破坏为主导。

Rocks are in a state of high static stress for a long time and are frequently affected by periodic disturbance loads, which are the key factors leading to various geological hazard.The low-frequency periodic load mechanical tests of large-size red sandstone under different average stresses and different disturbance amplitudes are tested by self-developed CX-8568 impact disturbance rock testing system.The evolution laws of rock strain and damage variables under different disturbance average stress and different distur-bance amplitude with high stress state are analyzed.The results show that the failure of rock under periodic disturbance load has a threshold value.When the load is lower than the threshold value, the rock will not be destroyed, and the elastic modulus is strengthened.It is concluded that high average stress and high disturbance amplitude are unfavorable factors for rock failure.When the upper limit stress exceeds the unia-xial compressive strength, the influence on failure cycle times of rock with average stress and distur-bance amplitude increasing is more obvious.With the upper limit stress being same, the average stress and disturbance amplitude being different, the sensitivity of rock failure to average stress is higher than the disturbance amplitude.The rock failure under periodic disturbance load is more violent than that under static load.With the increase of average stress or disturbance amplitude, the rock failure form changes from tensile-shear failure to tensile splitting failure.