红砂岩三轴加载过程中波速变化及能量演化规律试验研究

Experimental study on wave velocity variation and energy evolution of red sandstone during triaxial loading process

为研究红砂岩在三轴加载过程中的波速变化及能量演化规律,基于Rock Top多场耦合试验仪和JSR-DPR300超声测试系统,展开不同围压条件下红砂岩全应力-应变过程中的纵、横波速测试试验。研究表明:(1)纵、横波波速整体随围压增大呈幂函数关系增大,非线性特征增强,波速数据点分布在一条狭长的区间内;围压仅对岩石宏观强度具有增益效果,微观差异依然十分明显。(2)三轴压缩过程中,纵波波速可分为连续增长、震荡、快速衰减3个阶段;横波波速在高围压环境下,波速阶段性特征不明显,曲线近似线型且较为平滑。围压越大,轴向加载过程对于波速增益越弱,纵、横波速的衰减具有同步性,其中纵波波速对应力差状态更为敏感,不同围压条件下,能量密度曲线总体形态一致,波速衰减区间对应耗散能主要增长区间。(3)岩石损伤应力之前,纵、横波速之间具有较好的线性相关性,纵、横波速曲线拐点可作为判断损伤应力的标志。(4)随轴向应变增大,不同围压条件下的动弹性模量总体呈先增大,后相对平稳,再急速下降的过程;动泊松比总体呈增长态势,进入IV阶段后曲线剧烈震荡,动泊松比迅速增大;两曲线的阶段性特征并不明显。

In order to study the change of the wave velocity and the law of energy evolution of red sandstone under triaxial loading,compression and shear wave velocity tests of red sandstone in the full stress-strain process under different confining pressures were carried out by using the Rock Top multi-field coupling tester and the JSR-DP300 ultrasonic testing system. The results show that the compression and shear wave velocities increase as a power function of the confining pressure,accompanied by increasingly nonlinear characteristics,and that the wave velocity data points are distributed in a long and narrow interval. The confining pressure only has a gain effect on the macroscopic strength of rock,and the microscopic difference is still very obvious. In the process of triaxial compression,the compressional wave velocity can be divided into three stages including continuous growth, oscillation and rapid attenuation. Under the condition of high confining pressures, the phase characteristics of the shear wave velocity are not obvious,and the curve of the shear wave velocity is nearly linear and relatively smooth. The greater the confining pressure is,the weaker the gain of the wave velocity is in the axial loading process. The attenuations of the compression and shear wave velocities are synchronous,and the compression wave velocity is more sensitive to the state of stress difference. Under different confining pressures,the overall shapes of the energy density curves are consistent,and the attenuation interval of the wave velocity corresponds to the main growth interval of the dissipated energy. Before the rock damage stress,there is a good linear correlation between the compression and shear wave velocities,and the inflection point of the compression and shear wave velocities can be used as a mark to judge the damage stress. With increasing the axial strain,the dynamic elastic modulus under different confining pressures generally increases at first,then keeps relatively stable,and finally rapidly decreases. The dynamic Poisson’s ratio shows an overall growth trend. After entering the IV stage,the curve fluctuates violently and the dynamic Poisson’s ratio increases rapidly. The stage characteristics of the two curves are not obvious.