岩石加载过程声波波速变化规律实验研究

Experimental Study on Change in Acoustic Wave Velocity When Rock Is Loading

通过对花岗岩、片麻岩、大理岩和砂岩进行加载,探寻岩石波速随应力变化的响应特征.实验结果表明:花岗岩和片麻岩在线弹性加载阶段,波速-应力呈线性上升;波速达到峰值之后,波速-应力为二次函数非线性变化,再继续加载则岩样发生破坏.大理岩及砂岩在整个加载过程中波速基本保持恒定.依据成岩类型将波速变化分为两种类型:Ⅰ型,波速线性增加—峰值波速—缓慢下降—突然下降(破坏);Ⅱ型,波速不变—突然下降(破坏).在循环荷载作用下,岩石在线弹性加载阶段,波速呈线性上升;当增加到一定载荷,波速突然下降,岩样发生破坏.以上研究表明,在线弹性加载阶段,波速增加主要是密度变化引起的,裂纹萌生、扩展、贯通直接影响波速随应力的变化规律.

Different rock samples were loaded up to explore the response characteristics of the acoustic wave velocity（AWV） in rock with stress changing. The testing results showed that the relationship between AWV and stress goes up linearly in the linear elastic load phase of granite and gneiss, and the relationship becomes nonlinearly quadratic if AWV comes up to its peak value and, finally, rock failure comes true if loaded further. As to the marble and sandstone, AWV keeps constant basically in the whole loading process. The AWV change in rock could be divided into two types according to the diagenesis of different rock, i.e., Type Ⅰ ： linear increasing-peak AWV-slow decreasing-abrupt decreasing （failure）; Type Ⅱ： keeping constant-abrupt decreasing（failure）. It means that under cycling load AWV goes up linearly in elastic load phase then goes down abruptly if the load is increased to a certain extent and, further, rock failure happens. The reason why the AWV increases during elastic load phase is mainly due to density variation in rock samples. The process from initiation and propagation to breakdown of micro- cracks directly affects the rule of AWV change with stress.