动态扰动对应力松弛岩石变形行为影响的试验研究

Experimental study on influence of dynamic disturbance on deformation behavior of rock under stress relaxation

利用自主研发的岩石松弛-扰动试验装置,测试了岩石加载、松弛、动态扰动和扰动后4个阶段的轴向应力、轴向应变和声发射响应,观察到了岩石试样在动态扰动后应变增加、应力降低的现象,砂岩试样的这种特征比花岗岩明显。初步分析认为,产生该现象的原因一方面由于松弛-扰动过程导致岩石内部出现不可逆的损伤,另一方面则是扰动去除后试样的残余变形。在初始压密和弹性阶段,砂岩试样的声发射撞击数少;在接近应变峰值阶段,撞击数骤增;在应力松弛阶段撞击数骤减;在动态扰动阶段,撞击数骤增。声发射是由于岩石损伤引起的,声发射数据反映了岩石的损伤是引起松弛试样在动态扰动后应变增加、应力降低的一个原因。另外,基于砂岩和花岗岩的准静态循环加、卸载试验,对砂岩、花岗岩在不同应变等级下的残余应变进行了定量化;砂岩的残余应变远高于花岗岩,这与砂岩试样在历经松弛-动态扰动后应变增加、应力降低较为明显的趋势相对应。同时,无论是松弛-动态扰动试验还是准静态循环加、卸载试验,岩石的残余变形都会随着卸荷初始应变的提高而增加。岩石的损伤与残余变形是密切相关的,两者的综合作用引起了动态扰动后岩石试样的应变增加、应力降低现象。

The self-developed stress relaxation-dynamic disturbance test apparatus was used to measure the axial stress, axial strain and acoustic emission of rock subjected to loading and stress relaxation, dynamic disturbance. From the experimental results, it was found that the stress of rock specimen declined and its strain increased after the dynamic disturbance. In addition, the characteristics of sandstone were more obvious than that of granite. The preliminary study suggests that one reason for this phenomenon is likely related to the irreversible damage in the rock during the stress relaxation-disturbance process. Another reason is related to residual strain induced by the dynamic disturbance. During initial compaction and elastic phase, it is found that AE hits seldom occurs, while in the peak near the peak stress, AE hits instantly increases; during stress relaxation phase, the AE hits decrease, and it may increase instantly when triggered by dynamic loading. Clearly, the acoustic emission signal is induced by the damage evolution of rock, thus the AE data may reflect that the induced rock damage is one reason for the phenomenon of stress decline and strain increase. In addition, the quasi-static cycling loading and unloading test is conducted to quantify the residual strain of rock under the different loading levels. The residual strain in sandstone specimen is much larger than that in granite specimen, which corresponds well with the obvious phenomenon of stress decline and strain increase. In addition, the residual deformation increases with the rising initial unloading deformation both in stress relaxation-disturbance testing and quasi-static cycling loading and unloading test. Also, it should be mentioned that, the damage in rock is closely associated with residual strain, thus the both the rock and residual deformation may contribute to the phenomenon of stress decline and strain increase of rock specimen during stress relaxation-dynamic disturbance test of rock.