Creep characteristics of fractured Beishan granite under the condition of multi-field coupling
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摘要: 高放废物处置库运行后, 近场围岩将长期处于热—水—力耦合环境中, 其力学及渗透特性对处置库性能评价至关重要。我国高放处置库北山预选区围岩是典型的稀疏裂隙花岗岩体, 含裂隙花岗岩的蠕变特性直接关系着处置库的长期安全性能。为此, 首先通过水射流和线切割技术、裂隙表面封堵和岩样端部组合密封, 解决了热—水—力耦合三轴试验中含裂隙花岗岩样品的制备和密封难题。在此基础上, 开展了分级加载三轴蠕变试验。试验结果表明:在多场耦合条件下, 含裂隙花岗岩三轴蠕变强度约为三轴强度的80%, 蠕变变形随轴向荷载水平的升高而增大, 且横向蠕变比轴向蠕变更明显; 对应岩样的压密段和裂纹扩展段, 轴向应变率和渗透率均呈现先减小后增大的趋势; 渗透压差相等时, 裂隙内部较大的渗透水压会导致岩样峰值强度降低, 并产生更大的横向蠕变变形。该成果为处置库选址和围岩评价、处置库工程设计和建设提供了科学保障。Abstract: After a disposal repository for high-level radioactive waste operates, the near-field surrounding rocks will be long in a thermal-hydrological-mechanical coupling environment. Therefore, their mechanical and permeability characteristics are crucial to the performance evaluation of the disposal repository. The surrounding rocks of the Beishan preselected area for the disposal of high-level radioactive waste in China are typical sparsely fractured granites, whose creep characteristics are directly related to the long-term safety of the disposal repository. Using water jet and wire cutting techniques, along with fracture surface blocking and combined sealing at rock sample ends, this study addressed the challenges of the sample preparation and sealing of fractured granite in thermal-hydrological-mechanical coupling triaxial tests. Based on this, multi-loading triaxial creep tests were conducted. The test results indicate that under the condition of multi-field coupling, the triaxial creep strength of the fractured granite was approximately 80% of its triaxial strength. Creep deformation increased with the axial load level, with lateral creeps more pronounced than axial creeps. For the compacted and crack propagation sections of the rock samples, both the axial strain rate and permeability decreased initially and then increased. In the case of consistent osmotic pressure difference, a higher osmotic water pressure within fractures would lead to decreased peak strength of the rock samples and result in greater lateral creep deformation.The results provide scientific support for the site selection, surrounding rock evaluation, engineering design and construction of the repository.
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