峰后冷热循环下砂岩破坏过程力学特征及能量演化规律

Mechanical characteristics and energy evolution law of sandstone failure process under post-peak cold and heat cycle

在煤火治理中常因复燃等原因而多次注浆/水灭火,围岩经历反复升温遇水冷却,致使强度降低,发生破坏,延伸地表形成塌陷、裂缝,造成安全隐患,为此研究了峰后高温冷热循环下岩石力学变化情况;以砂岩为研究对象,测试了岩样超声波波速与吸水率,开展了单轴压缩试验,分析了砂岩力学损伤特征,并进一步探究了其能耗演化规律。结果表明:峰后500℃开始,岩样超声波波速衰减率与吸水变化率由正转为负,波速变小,吸水率增加;500℃为峰后高温岩样力学突变的阈值温度,之后应力应变曲线峰值点快速右移,峰值应力大幅衰落,冷热循环造成的初始热损伤加剧,延性破坏突出;在岩样承压破损不同阶段,能耗演化特征不一;峰后500℃开始,峰前耗散应变能占比逐渐大于弹性应变能,耗散应变能与力学强度负相关。

In coal fire control,grouting/water extinguishing is often repeated for reasons such as re-ignition.The surrounding rock undergoes repeated heating and water cooling,resulting in strength reduction and damage,and collapse and cracks on the extended surface,resulting in potential safety hazards.Therefore,the change of rock mechanics under high temperature and cold cycle after peak is studied.Taking sandstone as the research object,the ultrasonie wave velocity and water absorption rate of rock samples were tested,and the uniaxial compression test was carried out.The mechanical damage characteristics of sandstone were analyzed,and its energy consumption evolution law was further explored.The results show that:from 500℃after the peak,the attenuation rate of ultrasonic wave velocity and the change rate of water absorption of rock samples change from positive to negative,the wave velocity decreases and the water absorption increases;500℃is the threshold temperature of mechanical sudden change of high-temperature rock sample after the peak,and then the peak point of stress-strain curve moves rapidly to the right,the peak stress declines greatly,and the initial thermal damage caused by cold and hot cycles intensifies,and the ductile failure is obvious;the evolution characteristics of energy consumption are different in different stages of rock samples under pressure.From 500℃after the peak,the proportion of dissipated strain energy before the peak is gradually larger than that of elastic strain energy,and the dissipated strain energy is negatively correlated with the mechanical strength.