单轴压缩下热处理花岗岩的损伤特征:来自主/被动超声技术的见解

Damage characteristics of thermally treated granite under uniaxial compression: Insights from active and passive ultrasonic techniques

为了探明热处理对花岗岩损伤破裂的影响,对室温(25℃)及热处理(200,300和400℃)花岗岩试样进行单轴压缩试验,并采用主动超声和被动声发射监测技术研究试样的损伤特征。研究结果表明:与未进行热处理的试样相比,试样经200℃处理后单轴抗压强度(UCS)无明显变化,经300℃处理后UCS增加12.65%,经400℃处理后UCS降低4.97%。随着热处理温度由25℃升至400℃,试样初始P波速度由4909 m/s逐渐降低至3823 m/s,未加载时花岗岩试样的波速各向异性ε由0.03增至0.09。随着轴向荷载增加,ε受预存裂纹(包括热致裂纹)和应力诱发裂纹影响,在裂纹闭合阶段和不稳定开裂阶段迅速增大。超声波主频幅值在垂直方向(轴向)随应力增大而增大,在水平方向随应力增大而减小。此外,经热处理后试样的声发射事件定位震级减小,低频事件和高振幅事件增多。然而,没有足够的证据表明400℃以下的热处理对声发射时序特征、震源位置和b值有显著影响。

To explore the effects of thermal treatment on cracking processes in granite, granite samples were thermally treated at 25-400 ℃ and then loaded under uniaxial compression. Active ultrasonic testing and passive acoustic emission(AE) monitoring were combined to monitor the damage characteristics of the samples. The uniaxial compression strength(UCS) of the sample treated at 200 ℃ shows no apparent change compared with that of the nonheated sample, while the UCS increases at 300 °C and decreases at 400 ℃. As the temperature increases from 25 to 400 ℃, the initial P-wave velocity(Vp) decreases gradually from 4909 to 3823 m/s, and the initial Vpanisotropy ε increases slightly from 0.03 to 0.09. As the axial stress increases, ε increases rapidly in the crack closure stage and unstable cracking stage. The attenuation of ultrasonic amplitude spectra also shows an obvious anisotropy. Besides, the main location magnitude of AE events decreases after thermal treatment, and low-frequency AE events and high-amplitude AE events increasingly occur. However, there is insufficient evidence that the treatment temperature below 400 ℃ has a significant effect on the temporal characteristics, source locations, and b-values of AE.