较低功率微波辐射三类硬岩失水升温损伤规律与声发射特征

Damage law and acoustic emission characteristics of three types of hard rocks under low power microwave irradiation

微波辅助破岩是实现硬岩高效低损伤开挖的新方法,不同硬岩的吸波能力、失水、升温与损伤规律有一定的差异,对不同硬岩的对比研究对精准高效破岩有重要的理论与工程意义。以花岗岩、石灰岩、砂岩三类硬岩为研究对象,通过对比预处理和微波辐射前后试件的质量变化,获得三类硬岩的失水规律;通过红外热成像仪监测微波场内硬岩表面升温和破裂全过程,获得不同含水状态下三类硬岩升温和宏观裂纹扩展特性;通过干燥状态下三类硬岩辐射不同时间后的纵波波速、声发射及SEM微观结构的变化阐述了硬岩损伤随辐射能量递增机制。结果表明:在较低功率微波辐射300 s内,水对硬岩质量和升温的影响明显,具体表现为:水的蒸发溢出是质量损失的主导因素、水对升温有明显促进作用、含水状态对表面区域平均温度的影响程度按辐射时间分为较小(0~50 s)、较大(50~200 s)和稳定(200~300 s)3个阶段,其中,饱和吸水对升温影响最显著,且饱和吸水率高的砂岩和石灰岩分别在55,240 s时于腔体内炸裂。干燥状态下不同硬岩随升温的损伤规律表现为:石灰岩因表面温度差异大导致裂纹扩展较砂岩和花岗岩更为明显;COMSOL数值模拟持续辐射420,600,720 s的升温速率和实验获得的损伤因子二者变化趋势关联性好;损伤后,三类硬岩试件声发射呈现平稳→增长→破坏3个阶段、单轴抗压强度折损由快趋稳的共性特征,以及振铃计数与能量出现数量级变化的差异特性;微观尺度下,微波辐射720 s后的花岗岩和砂岩断口出现熔融矿物黏结,导致纵波波速降幅趋缓,解释了损伤趋稳的内因;随辐射时间增加,质量损失、由波速表征的损伤因子和数值模拟获得的升温速率及强度折损均呈现由快趋缓的一致性变化规律,且出现由快趋稳的拐点。研究结果可为不同硬岩的差异化、低能耗、高效率损伤研究提供一定的借鉴与参考。

Microwave-assisted rock breaking is a new method to achieve efficient and low-damage excavation of hard rocks.There are some differences in the wave absorption capacity,water loss,warming and damage laws of different hard rocks,and the comparative study has important theoretical and engineering significance for accurate and efficient rock breaking.By comparing the mass changes of the specimens before and after pretreatment and microwave radiation,the water loss law of the three types hard rocks were obtained.The whole process of surface temperature rise and fracture of hard rock in microwave field is monitored by infrared thermal imager,and the temperature rise and macro crack propagation characteristics of three types of hard rock under different water content were obtained.The mechanism of hard rock damage effect with increasing radiation energy was elaborated by the changes of longitudinal wave velocity,acoustic emission and SEM microstructure of three types hard rocks under different time of radiation in dry condition.The results show that the effect of water in the lower power microwave radiation within 300 s is as follows:the evaporation of water is the dominant factor in the mass loss of hard rock,water has a significant role in promoting the warming of hard rock,and the degree of influence of water content on the average temperature of the surface area is divided into three stages according to the radiation time“small(0-50 s),large(50-200 s),stable(200-300 s)”,in which the saturated water absorption has the most significant effect on the temperature rise and the sandstone and limestone with high saturated water absorption burst in the cavity at 55 s and 240 s respectively.The damage law of different hard rocks with temperature rise in dry state is as follows:the crack propagation of limestone is more obvious than that of sandstone and granite due to large surface temperature difference.COMSOL numerical simulation of continuous radiation for 420,600 and 720 s has a good correlation with the change trend of the damage factor obtained from the experiment.After the three types of hard rock damage,the acoustic emission of the specimens presents three stages of stability,growth and failure,and the uniaxial compressive strength loss is from fast to stable,and the ring count and energy are different in order of magnitude;At the micro scale,the fracture surface of granite and sandstone after 720 s of microwave radiation appears the bonding of molten minerals,which leads to the slow reduction of the longitudinal wave velocity,which explains the internal cause of the damage stabilization;With the increase of the radiation time,the mass loss,the damage factor characterized by the wave velocity,the heating rate and the strength loss obtained by the numerical simulation all show a consistent change law from fast to slow and a“inflection point”from fast to stable.The research results can provide some reference for the differentiation,low energy consumption and high efficiency damage of different hard rocks.