真三轴压缩下硬岩破裂过程超声波演化特征

Ultrasonic Evolution Characteristics of Hard Rock Fracture Process Under True Triaxial Compression

为研究真三向应力下硬岩破裂过程3个主应力方向超声波波速变化规律及其与岩石破裂的关系,对云南砂岩开展了一系列真三轴试验,获得了砂岩破裂过程中3个主应力方向的波速变化特征,发现了3个方向波速具有明显差异,主要表现在三个方面:最大波速、波速初始下降时的σ和峰后波速变化特征。波速分析表明,最小主应力方向波速最能够反映岩石破裂过程。将基于最小主应力方向波速计算的损伤变量与裂纹体应变进行了对比分析,发现损伤变量能较好地反映岩石破裂演化过程。为了更好地描述岩石破裂演化过程,用Power函数拟合了岩石破裂增长阶段损伤变量的演化曲线,建立了多阶段破裂演化方程。试验数据拟合结果表明,该方程与试验数据拟合良好。

In order to study the evolution laws of ultrasonic wave velocity in three principal stress directions during the fracture process of hard rock under true triaxial stress and its relationship with rock fracture,a series of true triaxial tests were carried out on Yunnan sandstone to obtain the variation characteristics of wave velocity in three principal stress directions during the fracture process of sandstone.It is found that there are obvious differences in wave velocity in three directions,which are mainly manifested in three aspects:the maximum wave velocity,σwhen the wave velocity decreases initially and the wave velocity after peak.The analysis shows that wave velocity in the direction of minimum principal stress can best reflect the rock fracture process.The damage variable calculated by the wave velocity in the direction of the minimum principal stress is compared with the crack volume strain,and it is found that the damage variable can better reflect the evolution process of rock fracture.In order to better describe the evolution process of rock fracture,the evolution curve of damage variable in rock fracture growth stage is fitted by Power function,and the multi-stage fracture evolution equation is established.The fitting results of experimental data show that the equation is in good agreement with the experimental data.