双向受压岩石在扰动荷载作用下致裂特征研究

FRACTURING BEHAVIOR STUDY OF BIAXIAL COMPRESSION OF ROCK SUBJECTED TO DYNAMIC DISTURBANCE LOAD

采用频率为2Hz,幅值分别为6,10,14,18和22MPa的正弦疲劳荷载作为动力扰动,来研究受双向静荷载并达到极限屈服状态的岩石在动力扰动荷载作用下致裂破坏的力学特性。试验结果发现:双向静载屈服状态红砂岩试件在动态周期荷载作用下,疲劳寿命明显短于在弹性阶段进行的疲劳测验的寿命。试件的疲劳寿命离散性较大,即使在同一动载幅值下也表现出很大差异,但相同应力幅值下最终破坏点处的变形量却基本相同,并且随着动载的幅值的增大而减小。研究还显示:具有相对较长疲劳寿命的试件的轴向变形量与循环次数(或时间)的关系曲线呈现出明显的3个阶段特性,其变化趋势与岩石蠕变曲线基本相同。岩石的最终破坏是由3个阶段的疲劳损伤累积所致,各阶段变形量占总变形量的比例、破坏模式和块度分布均与受到的动载应力幅值有关。

The influence of stress amplitudes of cyclic dynamic disturbance on the fracturing behavior and other dynamic response of rock is investigated.Red sandstone specimens used in the testing are subjected to a preloaded biaxial compression load which reaches rock yield strength and then coupled with a cyclic fatigue loading.Sine wave cyclic loads with of frequency 2 Hz and five different stress amplitudes of 6,10,14,18 and 22 MPa are adopted as dynamic disturbance.The obtained results show that fatigue life of specimen is usually no more than several decadal cycles under present loading conditions;the fatigue life of rock,when the preloaded biaxial compression load is beyond its yield strength,is much shorter than that when the preloaded biaxial compression load is within the elastic limit.Large disperse of fatigue life can be found in the tests,even for the cyclic loads with the same stress amplitudes.However,the total axial deformation at failure point for the fatigue loads with the same stress amplitude is almost the same.It is worthy noting that the axial deformation will decrease with the increasing of stress amplitude.For the specimen with a relatively longer fatigue life,their characteristic curves of axial deformation versus fatigue cyclic times can be divided into three stages and they are quite similar to that of rock creep curves.The accumulative deformation of three stages will lead to the final failure of the rock specimen,and the proportion of each stage in total deformation,failure mode and size distribution of rock fragments are all greatly affected by the stress amplitudes.