高放废物地质处置大尺度单裂隙花岗岩应力-渗透特性研究

Research on the granite from Beishan site, Gansu province, where is considered as the most potential site for China's High-Level nuclear Waste (HLW).Based on the large scaled granite seepage testing system developed independently, the coupling mechanism of stress-seepage test has been prepared. And the 3D topography of fractured rock surface has been reconstructured, by using the 3D laser scanner. Combined with the two tests, the stress-seepage coupling mechanism of the large sacled granite has been researched deeply and completely, as the inner factor (geometry of the fracture surface) and the outer factor (3D stresses), both influencing the permeability of the granite, has been considered. From the roughness of the single surface of the rock, the new parameter has been introduced, and it can describe the 3D topography of the granite surface quantify. Imposing the defferent normal stress and shear stress, the peameability of the granite under defferent topography will be obtained. Then the coupling mechanism of the topography-normal stress-shear stress-seepage will be analysed elaborately. And the influence of the seepage force (include static water pressure and seepage drawing force) on the stress (include normal stress and shear stress) will be illurated exactly. Finally, the coupling mechanism of the stress-seepage of single fractured granite will be detected. At the same time, the testing results will be compared and verified with the mechanism. From the fundamental research, the seepage field will be realized and it can support the selection and design of the Underground Research Laboratory (URL) and the final repository of the high level radioactive waste. And it also can provide the theoretical and technical support to the stability analysis and the radionuclide migration of the URL.The achievements can also be extended to other geomaterials and engineering fields.

通过自主研制的大尺度单裂隙花岗岩渗透试验设备，针对高放废物地质处置重点预选区-甘肃北山的花岗岩，开展渗流-应力耦合试验，并结合由三维激光表面扫描仪而重构的裂隙岩体表面三维形貌，分别从影响裂隙岩体渗透系数的内部因素（裂隙表面的几何表征）和外部因素（应力表征），深入全面的研究大尺度单裂隙花岗岩应力-渗透耦合机理。在单一表面粗糙度参数的基础上，通过引入新的衡量参数，得到裂隙表面三维形貌的定量化度量。在不同的法向应力、不同的剪切应力条件下，获得不同表面形貌情况下大尺度单裂隙花岗岩的渗透系数，探究大尺度裂隙花岗岩渗透性受裂隙表面粗糙度、法向应力、剪切应力影响的机理，并分析渗流作用力（渗流静压力与渗流拖曳力）对法向应力与剪切应力的耦合作用，最终揭示单裂隙渗流情况下渗流场的变化规律及应力-渗流耦合机理，与实际试验结果进行对比、分析、验证。本研究可以为高放废物地质处置工程的选址与设计、稳定性分析提供依据。

本项目为国家自然科学基金委资助的青年科学基金项目“高放废物地质处置大尺度单裂隙花岗岩应力-渗透特性研究”。针对裂隙介质渗透特性的试验及理论进展，结合裂隙介质渗流诱发的工程问题，详细介绍了自主研发的裂隙介质渗透试验台架；该台架可实现裂隙介质在法向、切向的同步、异步加载, 其最大加载位移均为100mm，最大加载荷载均为1000kN。密封技术是决定裂隙渗流试验成败的关键技术，通过相关调研及研究，针对本次试验所用的大尺度岩样，提出了全新的密封试验技术（“岩石表面内外放置密封圈”），采用此技术实现了大尺度裂隙介质渗透试验的密封。同时，基于渗流达西定律及立方定律，得到了适用于该试验台架的裂隙介质渗透系数计算方法。进一步地，利用该渗透台架，采取“岩石表面黏贴细砂”的方法模拟岩石表面的粗糙性，初步开展了大尺度单裂隙花岗岩的渗透试验。并基于流量平衡原则，剔除无效试验数据，获得了该单裂隙花岗岩渗透系数的变化规律，其随着渗透时间的增加，渗透系数逐渐增大，并稳定至某个数值。深入分析了渗透系数变化的影响因素，认为裂隙介质表面黏贴的细砂对其渗透性有着决定性的影响。同时进行了裂隙介质的表面为光滑、无黏贴细砂状态下的渗透试验，与之相对比，验证了裂隙表面的粗糙性是影响裂隙介质渗透系数的重要因素。渗透试验结果表明：此渗透试验台架采用该计算测试方法获得的参数是准确可信的，可以应用于地下核废料处置、水利水电地下硐室、水下隧道、采矿等工程有关问题的研究中，为能源的开发利用提供有效的研究手段。