花岗岩热损伤抗拉强度和声发射特征试验研究

Experimental study on characteristics of tensile strength and acoustic emission of granite after thermal damage

针对核废料处置库、地热开采工程、煤炭地下气化等地下工程围岩结构高温稳定性问题,研究花岗岩在25~700℃加热后的抗拉强度变化和声发射特征,并分析花岗岩的微裂纹损伤特征和宏观破坏模式。试验结果表明:试样的应力时间曲线表现为明显的近线性增长和迅速破坏特征,应力近线性增长速率随温度增加先缓慢上升后下降;花岗岩的抗拉强度随温度增加不断减小,其中在300~400℃抗拉强度下降最快;随温度增加声发射b值波动更为剧烈,声发射累计振铃计数在不同温度下也表现出差异性增长特征,声发射能量随温度总体上是不断减小的,声发射事件数水平和出现频率在高温条件下显著增大;随温度增长裂纹出现越早,裂纹损伤应力门槛比值则是先减小后增大;花岗岩破坏模式在不同温度下均是以主裂纹为主,断裂面的粗糙度、不平整度随温度不断增大。

For the change of stability of surrounding rock under high temperature in underground engineering included nuclear waste disposal repository,geothermal exploration engineering,underground coal gasification,the tensile strength and acoustic emission(AE)characteristics of granite heated at 25-700℃was studied,and analyzed the macro failure mode and micro crack damage characteristics,the test results show that:the stress~time curve of the sample showed the obvious nearly linear growth and rapid destruction features,stress nearly linear growth rate rose slowly before downward trend with temperature;The tensile strength of granite decreased with temperature,and decreased most rapidly at 300-400℃.The evolution law of AE b-values changed and became more severe fluctuations with temperature,accumulated AE counts at different temperature also showed different growth characteristics of and AE energy was reduced constantly with temperature.And overall number of level and frequency of AE events under high temperature significantly increased.The development of stress threshold ratio of crack indicated that the crack appeared earlier with the increase of temperature,the stress threshold ratio of crack damage decreased first and then increased.The failure mode of granite was dominated by the main crack at different temperatures.The roughness and unevenness of the fracture surface increased continuously with temperature.