岩体贯切破坏在不同侧向自由边界的声发射演化

ACOUSTIC EMISSION EVOLUTION IN INDENTATION FRACTURE OF ROCKS UNDER DIFFERENT LATERAL STRESS-FREE BOUNDARIES

采用机械式隧道开挖可提升施工自动化与工程安全性的成效,但因机械式掘削刃口开挖过程的力学机制仍属浑蒙,而掘削机具与弱面位置的互制关系,对于岩体破坏行为有着重要的影响。以脆性岩体为研究目标,探求楔型刃口贯切受测岩体的接触破坏机制,为工程实际提供参考。由正向楔型贯切仪器的建置,并采用非损伤的声发射技术,以楔型刃口为尖状及90°楔角的试验条件下,改变不同贯切位置,以无侧围压方式进行模拟开口不连续的弱面状况,并采用裂缝开口位移控制,使加载于尖峰行为后,不致失稳开裂,以求取完整的贯切加载历程。试验结果显示,不同贯切位置的裂缝开裂路径,存在着几何相似特性;随着逐渐靠近侧向自由边界,其最大贯切力与最大贯切深度均随之降低,但对于标称贯切压力则影响不大。而声发射技术所接收的微震事件,可代表微观裂缝的生成,其与宏观裂缝的初裂与延伸作一比较,证实声发射定位结果十分良好;随着贯切位置逐渐靠近侧向自由边界,丛聚现象发生时机将提早发生,且弹–塑性交界半径则有减小的趋势。

Automatic efficiency and engineering safety are both enhanced by using mechanical excavation in tunnel construction; nevertheless, the mechanism for excavation by mechanical cutter is still uncertain. The interaction between the cutter and the position of weak plane during cutting is important for studying the behavior of rock fragmentation, so quasi-brittle materials were used to investigate the fracture mechanism of wedge indentation in order to provide references for the construction in practice. Equipment of a normal wedge indentation was established; and non-destructive acoustic emission（AE） technique was applied for the tests. It simulates discontinuous weak plane of the open joint under the lateral stress-free boundary for indentation at various positions by a wedge with a sharp-shaped tip at angle of 90°. In order to obtain a complete loading history, crack mouth opening displacement（CMOD） control was adopted to avoid unstable fracture after the peak level. From the experimental results, features of geometrical similarity were observed for the crack paths at different indentation positions. When positions approach to the lateral stress-free boundary, the maximum indentation force and the maximum indentation depth both decrease; however, the impact for nominal indentation pressure is not significant. Moreover, it is figured out that microseismic events received by the AE technique can stand for the initiation of the microcracks. Outcomes of AE locations are verified to be very precise by comparing the microseismic events with the macroscopic initial fracture and its development. Localization takes place earlier as indentation approaches to the lateral stress-free boundary; and the radius of elastoplastic interface becomes smaller.