加载速率影响下板裂化脆性岩石失稳破坏试验研究

Experimental study on instability destruction of slab-failure brittle rock under influences of loading rates

深部脆性岩体开挖常发生板裂破坏,并可能进一步发生片帮剥落、岩爆等工程灾害,严重威胁深埋隧(巷)道施工安全。在深部岩体工程中,受构造应力、开挖条件和工程扰动等因素的影响,岩体开挖后应力重分布的速率、来压快慢均存在差别。为探究加载速率对板裂围岩失稳破坏的影响,采用脆性岩石加工成的板裂试样进行单侧限单轴压缩试验,对不同加载速率下试样宏观破裂、强度特性、声发射(AE)特征以及能量机制进行综合研究。结果表明:(1)低加载速率下试样发生大块剥落,整体失稳并发生分离,高加载速率下试样未发生大块分离,但有小块动力弹射现象;(2)低频、高幅信号的增多及b值的变化表明试样产生了突发式的裂纹失稳扩展,且这个过程中大小尺度破裂不断交替产生;(3)在平稳加载阶段,高加载速率使试样AE活动更加剧烈,而临近失稳及失稳破坏阶段则相反,且低加载速率下低频信号、大尺度破裂事件占比更大。因不同开挖方案、施工方法导致的围岩应力重布快慢差异,在工程上会导致围岩发生板裂后,进一步诱发不同模式破坏。

Excavation of deep brittle rock often leads to slab failure,and may further to flake spalling,rock explosion and other engineering disasters,which is a serious threat to the safety of construction of deeply buried tunnels.In deep rock mass engineering,the rate of stress redistribution after excavation varies due to the factors such as tectonic stress,excavation conditions and engineering disturbances.In order to investigate the effects of loading rates on the destabilization damage of slab-failure surrounding rock,the unilateral limit uniaxial compression tests are conducted using brittle rock processed into slab-failure specimens,and the macroscopic rupture,strength characteristics,acoustic emission(AE) characteristics and energy mechanism of the specimens are comprehensively investigated under different loading rates.The results show that:(1) The specimens exhibit large pieces of spalling,overall instability and separation under low loading rates.The specimens did not separate in large pieces under high loading rates,but there are small pieces of power ejection.The compressive strength of the specimens increases with the increase of the loading rates.(2) The increase of low frequency and high amplitude signals and the change of b-value indicate that the specimens have a sudden failure instability propagation,and the large-and small-scale fractures are alternately generated during this process.(3) At the steady loading stage,the high loading rates make the AE activity of the specimens more intense,while the opposite is true at the near destabilization damage stages,and the lowfrequency signal and large-scale fracture events account for a greater proportion under low loading rates.The difference in the speed of stress re-distribution due to different excavation schemes and construction methods in engineering is the cause of further damage in different modes after the occurrence of slab failure in the surrounding rock.