现场岩体直剪试验声发射特征及其破坏机制

Acoustic Emission Characteristics and Failure Mechanism of Rock Mass in Field Shear Test

尽管应用声发射对岩石破裂过程的研究取得了诸多成果,但主要集中于小尺寸(≤10 cm)的岩块,对较大尺度(≥50 cm)岩体破坏机理研究还较少。采用最新的SAMOS声发射系统,对节理岩体现场直剪试验过程进行声发射测试。通过现场岩体直剪破坏过程中声发射特征参数与频谱特性研究,揭示了节理岩体破坏机制,深化了对岩体破坏机理的认识。测试结果表明节理岩体破坏过程中,声发射信号的主频范围为40～120 kHz,其直剪破坏过程可分为4个阶段:①弹性变形阶段,岩体内部没有声发射事件;②起裂阶段,声发射事件很少,岩体内部仅有少量的裂纹产生;③扩展阶段,声发射事件缓慢增加,岩体内部微裂纹不断扩展;④破坏阶段,声发射事件大量增加,微裂纹不断扩展贯通,岩体出现宏观破裂。根据研究结果可知:与传统的破裂从前端开始的观点不同,岩体试件中后端最先出现声发射定位事件,表明微破裂开始发生在岩体试件的中后端;随着剪应力的增加,声发射定位事件逐渐前移,当岩体进入破坏阶段后,微破裂集中于剪切面局部,岩体产生局部破裂化。

Although many achievements have been made on the application of Acoustic Emission（AE） technique to monitoring crack propagation in rock mass,these studies mainly focused on rock block of small size（≤10 cm）.Only a few investigations have been done to research the failure mechanism of larger rock mass（≥50 cm）.The SAMOS acoustic emission instrument was employed to study the failure process of jointed rock mass in field shear test.Based on analysis of AE parameters and frequency spectrum acquired from the shear failure process of jointed rockmass,its failure mechanism can be revealed.The results showed that during the failure process of jointed rock mass,the main frequency of AE signals varied from 40 kHz to 120 kHz.The shear failure went through four phases： first,elastic deformation phase,during which no AE events happened in rock mass;second,crack initiationphase,in which a few AE events occurred and only a few cracks were generated;third,crack propagation phase when AE events increased slowly and cracks propagated steadily;and fourth,crack coalescence phase when AE events increased apparently,cracks propagated and coalesced and macro fractures appeared.Different from the traditional viewpoint,which deems that the crack appears at the forward section of rock specimen,this research finds that the initial cracks appears at the middle and back-end of the specimen.With the increase of shear stress,the locations of new cracks move to the forepart.However,during the crack coalescence phase,the cracks fastened on local positions of the shear surface.Local cracking happened in jointed rock mass.