高温-水冷后不同损伤度花岗岩双轴力学性能及声学特性试验研究

Experimental study on biaxial mechanical properties and acoustic characteristics of different damage granites after high temperature-water cooling

地下工程岩石遭遇高温-水冷后会产生不同程度的损伤,其力学特性关系着工程的安全稳定,其声学特性关系着岩石内部破坏的分析与预测预警,有关研究具有重要科学价值与工程意义。对高温-水冷后不同损伤度花岗岩,利用真三轴试验系统开展双轴压缩试验,采用声发射(AE)和微震(MS)系统监测岩石的破坏过程,分析不同损伤度花岗岩的双轴力学强度和变形、声信号演化特征和前兆信息等,讨论岩石初始损伤对其破裂类型的影响,对比微震和声发射信号的时频域特征。结果表明:(1)花岗岩的初始损伤度D越高,岩石的双轴强度和弹性模量越低,当D>0.4后二者降幅比D<0.4时显著增大。同时,岩样破坏由脆性向延性转变,内部破裂从张拉型为主向剪切型为主转变。(2)随着岩石损伤度D的增加,岩样的AE累积绝对能量大幅降低。声信号参数演化特征在岩石D>0.4和D<0.4时表现出明显差异。相较低损伤度岩样,高损伤度岩样的AE撞击、MS幅值演化曲线突增时间会提前,高幅值信号会增多,信号活跃期的持续时间也会变长。(3)基于AE和MS信号可分析获得岩石破坏的一些前兆信息以及岩石初始损伤度的有关判据。例如,MS分形维数在峰值荷载后出现明显的剧烈突增-突降现象可作为不同损伤度岩石失稳破坏的前兆信息,MS或AE b值突降至1以下可作为低损伤度岩石失稳破坏的前兆信息。声发射b值在塑性阶段数值降至1以下的现象多次出现,以及MS分形维数峰值荷载前出现明显的大幅突增-突降波动,可作为岩石初始损伤度较高的判定依据。有关研究成果可为地下工程中围岩稳定性的分析和岩石性状的评估提供参考。

The high temperature-water cooling effect causes different degrees of damage to rock in underground engineering.The mechanical properties of the damage rock are related to the safety and stability of the engineering,and its acoustic characteristics are related to the failure analysis,prediction and early warning of surrounding rock.Relevant research has important scientific value and engineering significance.In this study,the biaxial compression test of granite with different damage degrees after high temperature-water cooling treatment was carried out by using true triaxial test system.Acoustic emission(AE)and microseismic(MS)systems were used to monitor the failure process of rock.The biaxial strength and deformation,acoustic signal evolution characteristics and precursor information of granites with different degrees of damage were analyzed.The influence of initial damage of rock on its fracture type was discussed,and the time-frequency domain characteristics of microseismic and acoustic emission signals were compared.The main conclusions are as follows.(1)The higher the initial damage degree(D)of granite,the lower the biaxial strength and elastic modulus of rock are.When D>0.4,the decrease of biaxial strength and elastic modulus is significantly larger than that when D<0.4.At the same time,the failure of rock samples changes from brittle mode to ductile mode,and the rock internal fracture changes from tensile type to shear type.(2)With the increase of rock damage degree,the AE cumulative absolute energy of rock samples decreases greatly.The evolution characteristics of acoustic signal parameters show obvious differences when D>0.4 and D<0.4.Compared with the rock samples with low damage degree,the moment of first sudden increase of AE hits and MS amplitude evolution curves of the rock samples with high damage degree generally appears earlier,more high amplitude signals emerge,and the duration of signal active period sustains longer.(3)Based on AE and MS signals,some precursor information of rock failure and the criterion of rock initial damage degree can be concluded.For example,the phenomenon that the MS fractal dimension increases and decreases sharply after the peak load can be used as a failure precursory information of the rock with different damage degrees,and the sudden decrease of MS or AE b value below 1 can be used as a failure precursory information of the rock with a low damage degree.The phenomenon that the AE b value decreases to less than 1 in the plastic stage occurs many times,and the MS fractal dimension fluctuates sharply before the peak load,which can be used as the basis for judging the initial damage degree of rock.The research results can provide reference for the analysis of surrounding rock stability and the evaluation of rock damage degree in underground engineering.