北山花岗岩热破裂室内模拟试验研究

岩石热破裂是高放废物地质处置工程中需深入研究的课题。对我国高放废物重点预选场址甘肃北山的花岗岩开展室内热破裂模拟试验研究，采用多通道温度测试仪、声发射、波速层析成像和数码显微镜等手段研究了该花岗岩热破裂过程。试验表明，（1）热破裂从试件端部开始产生，逐步向内缓慢扩展，表现出分段性和独立性；（2）根据声发射撞击率可将热破裂可分为稳定热损伤、宏观裂纹形成、宏观裂纹扩展、裂纹冷却闭合4个阶段，声发射定位的时空演化规律清楚地揭示了裂纹从试件上端部向内部扩展的规律；（3）波速层析成像指示了宏观裂纹位置及高温对岩石造成显著损伤的区域，热应力产生的损伤集中在试件边界，范围小，损伤严重，高温造成的损伤集中在钻孔附近高温区，范围较大，损伤略轻微；（4）监测多通道温度，获得了试件内的温度场并为数值模拟参数选取提供验证，采用有限元程序进行了热力耦合数值模拟，从机制上初步解释了热破裂现象，研究认为综合声发射实时监测热破裂过程和波速层析成像能实现对热损伤的量化的特性可实现岩石热破裂的动态监测和损伤量化，为今后地下实验室相关试验的开展和认识高放废物处置长期稳定性做了有意义的探索。

Laboratory simulation test of thermal cracking of Beishan granite

Thermal cracking of rock is a critical subject in high radioactive waste disposal engineering. A laboratory simulation test was conducted to study the thermal cracking of Beishan granite. The temperature measuring device, acoustic emission (AE) system, ultrasonic computer tomography(CT) and microscope were applied to the test. The results show that the macrocracks originated at the outer edges of the specimen and then extended inward. The growth of cracks was mutational, and the latter cracks were suspected little impact of the former cracks. Four stages were observed during the test: stable thermal damage stage, macrocrack formation stage, macro-crack growth and the crack closure stage during cooling period. The evolution of AE locations reveals the growth of cracks’ propagation process. The ultrasonic imaging of the cooled sample was obtained by the elastic wave CT. The cracks’ positions and area suffered heat damage could be visualized in the CT imaging. The study shows that system combined AE and ultrasonic CT is effective to characterize the evolution of thermal-cracking process and quantify the damage. Temperature field obtained from a group of thermal couples can be used to verify the parameter for numerical simulation. The results of numerical simulation show that the high tensile stress at the time of macrocrack appearing is consistent with the tensile strength of Beishan granite. Thermal induced damage and thermal-mechanical induced crack are analyzed systematically, so as to provide reference for the future related tests conducted in underground laboratory.