基于围压因素的分级应力扰动下砂岩损伤破裂特性试验研究

Experimental study on damage and fracture characteristics of sandstone under graded stress disturbance based on confining pressure factor

受制于采掘活动的频繁应力扰动,地下工程围岩的稳定性问题日渐突出,严重制约了地下矿产资源的安全高效开采。为了探究不同埋深下岩体在应力扰动过程中的损伤破裂机制,以常规三轴试验为基础,开展4组围压下的分级应力扰动室内试验,基于力学分析、声发射分阶段定位及损伤评价指标演化特征,确定分级应力扰动下岩石力学的损伤劣化规律及细观裂纹发育特征,建立岩石损伤状态—微观裂纹发育特征—损伤评价指标变化三者之间的关联。结果表明:(1)分级应力扰动下,岩石峰值强度和峰值轴向应变随围压升高逐渐增大。应力扰动各阶段轴向应变增量均呈现初期小幅波动,中期缓慢增加,后期快速增加的趋势;平均弹性模量呈现初期小幅波动后快速降低的趋势。(2)围压通过限制裂纹扩展降低岩石损伤累积速率,高围压下岩石能承受更多级应力扰动,且恒压阶段蠕变特征更明显。(3)加载前期,岩石内部裂纹发育仅在既有损伤区域的重复压密破坏和临近区域少量微裂纹的发育,扰动后期随着轴力的升高会使得围压限制作用减弱造成裂纹快速扩展。(4)岩石内部在加载不同阶段微裂纹发育的数量、尺度的变化能有效的体现在声发射b值和ΔF值,与岩石损伤程度耦合度较高,可用来定量评估岩石损伤状态。研究结果可为工程岩体的围岩稳定和损伤评估提供一定的指导和借鉴。

Due to frequent stress disturbances caused by mining activities,the stability of surrounding rock in underground engineering is becoming increasingly prominent,which seriously restricts the safe and efficient mining of underground mineral resources.In order to explore the damage and fracture mechanism of rock mass in the process of stress disturbance under different buried depths,based on conventional triaxial tests,graded stress disturbance laboratory tests under four groups of confining pressures were carried out in this paper.Based on mechanical analysis,acoustic emission(AE)source phased location and evolution characteristics of damage evaluation indexes,the rock mechanics damage degradation law and meso-crack development characteristics under graded stress disturbance were determined,and the correlation among rock damage state,meso-crack development characteristics and the change of damage evaluation indexes was established.The results show that:(1)The peak strength and peak axial strain of rock increase with the increase of the confining pressure under the disturbance of graded stress.The axial strain increment of stress disturbance in each stage shows a slight fluctuation in the early stage,a slow increase in the middle stage,and a rapid increase in the late stage.The average elastic modulus increases slightly at the beginning and then decreases rapidly.(2)The confining pressure reduces rock damage accumulation rate by limiting crack propagation.The rock can withstand more stress disturbances under high confining pressure,and the creep characteristics of constant pressure stage are more obvious.(3)In the early stage of loading,the crack development in the rock is only the repeated compaction failure in the damaged area and the development of a few microcracks in adjacent areas.In the late stage of disturbance,with the increase of axial force,the limiting effect of confining pressure will be weakened,resulting in rapid crack propagation.(4)The changes of the number and scale of microcracks in rock at different loading stages can be effectively reflected in the AE b value and AEΔF value,which are highly coupled with the rock damage degree and can be used to quantitatively evaluate the rock damage state.The research results can provide some guidance and reference for the stability and damage assessment of engineering rock mass.