单轴荷载下砂岩波速特征与损伤演化规律研究

超声波波速变化是判定岩体裂纹扩展、损伤演化的重要手段。联合单轴压缩与超声波波速测试试验,探索了加载过程中砂岩试样的波速变化特征,并据此对砂岩的破裂发展及损伤程度开展了评价。结果表明,在压密和弹性阶段内,砂岩的波速和动弹性模量都呈增大趋势,表明砂岩结构随加载变得更加致密;而随加载进行由弹性阶段逐渐进入塑性阶段,波速和动弹性模量均开始下降;横波、纵波波速的转折点基本对应压密—弹性、弹性—塑形的转折点,而波速比的变化较符合岩心内部裂隙发展特征;对比发现,横波波速变化比纵波波速敏感性更大;在整个加载过程中,岩石的动弹性模量与应力应变曲线都呈现良好对应关系,表现为弹性阶段后期动弹性模量开始下降,而进入塑性阶段后,动弹性模量下降速率渐趋于最大值。该研究可为砂岩内部损伤演化规律及灾变预报预警等有益参考。

Research on Ultrasonic Velocity Properties and Damage Development of Sandstone under Uniaxial Compression

The variant of the ultrasonic velocity has become an important technical measurement to investigate the cracks propagation and damage evolution of the rocks. In conjunction with the uniaxial compression tests and the ultrasonic velocity measurements in laboratory, the ultrasonic velocities of sandstone under uniaxial compression had been analyzed, and the results were used to evaluate the fracture development and damage degree of sandstone. The results showed that: in the initial phases of loading, in compaction phase and elasticity phase, the shear wave velocity, transverse wave velocity, as well as rock damage variable values showed the similar development trends, all increased with increment of loading, indicating tight compaction of the sandstone matrix. With further increasing of loading stress, the rock passed from elastic phase into plastic phase, the rock velocity and damage variable value decreased gradually. The transitions in the shear wave velocity curve and in the transverse wave velocity curve basically corresponded to the transitions of compaction-elasticity phase and elasticity-plasticity phase, and the variants of wave velocity ratio corresponded to the fracture development morphology of rock. By compression, the changes of shear wave velocity were more sensitive than those of the transverse wave. During the entire phase of loading, the dynamic elastic modulus of sandstone had a good correspondence with the stress-strain curves, showing that the dynamic elastic modulus decreases in the end of elastic phase, and the decreasing rate of dynamic elastic modulus gradually reached its maximum in plasticity phase. The studies above can supply reliable references for the investigation of the fracture characteristics of rock and the forecasting and warning of the rock catastrophes.