升温路径对花岗岩超声波传播特性影响的试验研究

Experimental Study of Effects of Heating Path on Ultrasonic WavePropagation Characteristics Across Granites

地热能开发以及核废料处置等深部高温岩体工程中,岩石破裂行为和损伤特征受升温路径影响显著.超声波传播速度和振幅等参数可以综合反映岩体破裂和损伤状态,具有重要的工程价值.为探究升温路径对岩石超声波传播特性的影响,开展了600℃下不同加热速率和恒温时间热处理后花岗岩的超声波透射和SEM扫描试验.研究结果表明:岩石超声波波速、幅值和频谱振幅等特征参数在不同升温路径下有较大差异.岩石超声波传播特性与加热速率具有明显的阶段依赖性,当加热速率低于9℃/min时,岩石超声波传播特征参数随加热速率增加显著降低;当加热速率高于9℃/min时,其降低幅度减缓.恒温时间对岩石超声波特性的影响存在阈值,当恒温时间小于3 h时,超声波传播特征参数随着恒温时间增加而减小,当恒温时间大于3 h时,其变化不明显.不同升温路径下岩石热裂纹扩展模式的差异是影响热处理岩石超声波传播特性的主要原因.超声波传播特征参数中首波幅值对升温路径变化的敏感性最高,适宜作为评价花岗岩体破裂行为和损伤程度的最优指标参数.研究结果对高温岩体工程损伤程度和稳定性评价具有一定的指导意义.

The fracture behavior and damage characteristics in deep rock engineering under high temperature conditions(e.g.,geothermal development and disposal of nuclear waste)are significantly affected by the heating path.The parameters such as ultrasonic wave velocity and amplitude can comprehensively reflect the fracture and damage states of rock masses,with an apparent engineering value.To investigate the effects of the heating path on the ultrasonic wave propagation characteristics,ultrasonic transmission and SEM mesoscopic scanning tests were performed on granites after thermal treatment with different heating rates and heating durations at 600℃.Results show that the characteristic parameters including ultrasonic wave velocity,amplitude and peak spectrum varied under different heating paths.The ultrasonic wave propagation characteristics and heating rate were significantly phase-dependent.When the heating rate was less than 9℃/min,the parameters of ultrasonic wave propagation characteristics decreased substantially with the increasing heating rate.In comparison,the reduction in magnitudes became moderate when the heating rate was higher than 9℃/min. There was also a threshold for the heating duration. Specifically,when the heating duration was below 3 h,the parameters of ultrasonic wave propagation characteristics sharply declinedwith the increasing heating duration,while the corresponding changes were not obvious when the heating durationwas longer than 3 h. The variation in the expansion pattern of thermal cracks was the main reason for changes inultrasonic wave propagation characteristics under different heating paths. Furthermore,the initial wave amplitudewhich is most sensitive to the heating path can be considered as the most effective indicator to evaluate the behavior ofthermal fracture and the degree of thermal damage for granites. The findings in this paper are of significance to theevaluation on the damage degree and stability of rock engineering under high temperatures.