不同应力路径下岩桥试验的声发射特征研究

Acoustic emission characteristics of rock bridge test under different stress paths

岩质边坡中岩桥贯通是导致边坡失稳的重要因素,通过开展不同岩桥长度岩样的常规三轴加荷、三轴卸荷以及三轴加卸荷试验,研究在不同应力路径下岩桥贯通破坏过程中的声发射特征,以及围压和岩桥长度对声发射特征的影响。结果表明:岩石压密阶段与线弹性变形阶段声发射事件较少,塑性阶段声发射事件明显增多,破坏阶段声发射计数率、累计能量以及幅值均达到峰值。声发射特征的明显变化可为紧接的岩样破坏提供预警作用,幅值变化较其他指标更为敏感,因此幅值的监测对于各阶段演化以及破坏预警更有效。本试验中,岩桥试样达到峰值强度后不会立即跌落至残余强度,而是出现2次应力跌落,应力跌落均对应声发射特征达到峰值,2次应力跌落中会出现"平静期"或"峰后回升"现象,其声发射特征与塑性阶段相似,但幅值、计数率与累计能量均大于塑性变形阶段,表明在这一阶段岩样裂纹仍以较快速率扩展,最终导致岩桥贯通破坏。不同应力路径下累计能量由大到小依次为:三轴加卸荷、三轴卸荷和常规三轴。随着岩桥长度与围压的增加,声发射计数率峰值和累计能量逐步增长,破坏程度更加剧烈。

The failure of rock bridge in rock slopes is an important factor for the instability of a slope. The triaxial loading, triaxial loading-unloading and triaxial unloading tests of different length of rock bridges were carried out. Acoustic emission（AE） characteristics of rock bridge during failure process under different stress paths was described, and the influence of confining pressure and rock bridge length on the AE characteristics was analyzed. The results showed that AE events are low during the compression and elastic deformation phase. AE events increased significantly during the plastic phase, and AE counts, the accumulated energy and amplitude reached their peak during failure phase. Significant changes in AE characteristics can be used as early warning for failure of rock sample, the variation of amplitude is more sensitive than other AE indicators. Therefore the monitoring of the amplitude is more effective for the failure warning. In this experiment the rock bridge is not immediately dropped to the residual strength after the peak strength, but two stress drop occurred after peak stress, each sudden drop of stress corresponds to the AE signal peaks. The phenomenon of ＂quiet period＂ or ＂post-peak rebound＂ occurred in the two stress drop, and AE characteristics of the ＂post-peak rebound＂ and ＂quiet period＂ is similar to the plastic phase. However, its amplitude, count rate and the accumulated energy are greater than plastic deformation stage which indicates the rock crack is still in a relatively rapid rate expansion, and resulting in the failure of rock bridge. Accumulated energy from the large to small are triaxial loading-unloading, triaxial unloading and triaxial loading under different stress paths. With the increase of length of rock bridges and confining pressure AE count rate peak and cumulative energy increased, and meaning more severe failure of rock bridge.