考虑温度效应的泥岩各向异性细观损伤机制研究

The decay process of high level radioactive waste will be accompanied by the appearance of a lot of heat. In the deep geological repository with the surrounding rock of mudstone， the temperature rise will lead to change of the meso-structure, anisotropy, strength and deformation characteristics of the surrounding rock, and then influence its damage evolution and failure mode. This project aims at mudstone in the alternative preselected area for China's high level radioactive waste disposal. Under different temperatures and different loading angles (the angle between the loading direction and the mudstone bedding surface), uniaxial compression tests and triaxial compression tests with different confining pressures will be carried out. Combined with several micro structure observation methods such as X ray diffraction, scanning electron microscopy (SEM), CT scanning and acoustic emission technology, the effect of temperature on the physical mechanical properties of anisotropic mudstone will be studied, and the meso-mechanism of the damage evolution and failure mode will be revealed. Based on the experimental results and theoretical analysis, an anisotropic damage model of mudstone considering temperature effect is established. It is then embedded into a numerical simulation tool to realize the thermal mechanical coupling simulation of anisotropic mudstone. Through comparison of laboratory test and numerical simulation results, the model’s rationality and validity are verified. The research methods and conclusions provide a theoretical basis for the site selection and conceptual design of high-level radioactive waste disposal repository, and also provide reference experience for the construction of deep underground engineering in anisotropic surrounding rock.

高放废物的衰变过程会伴随产生大量的热量，在以泥岩作为围岩的深地质处置库中，温度上升会导致围岩的细观结构、各向异性及强度变形等特征发生变化，进而影响其损伤演化规律和破坏模式。本项目拟针对我国高放废物泥岩处置库备选预选区泥岩开展不同温度、不同加载倾斜角（加载方向与泥岩层理间的夹角）条件下的单轴压缩试验及不同围压条件下的三轴压缩试验，结合X射线衍射、电镜扫描、CT扫描和声发射技术等细观结构观测方法，研究各向异性泥岩物理力学性质的温度效应，并揭示其损伤演化和变形破坏的细观物理机制。基于试验结果和理论分析，建立考虑温度效应的泥岩各向异性损伤模型。并将其嵌入到数值模拟工具中，对比验证其合理有效性，实现各向异性泥岩的热力耦合模拟。研究方法及结论为高放废物处置库的选址及概念设计提供理论基础，也为其它各向异性岩石的深部地下工程建设提供参考经验。

高放废物的衰变过程会伴随产生大量的热量，在以泥岩作为围岩的深地质处置库中，温度上升会导致围岩的细观结构、各向异性及强度变形等特征发生变化，进而影响其损伤演化规律和破坏模式。本项目获得了我国高放废物泥岩处置库备选预选区泥岩的基本物理力学特性和关键力学参数，通过开展考虑温度效应的三轴试验，发现随着热处理温度的升高，岩样在三轴应力条件下的力学性能有所下降，且在经历循环加卸载时力学性质劣化更明显，在实时高温试验条件下，上述温度效应更明显，即热处理所产生的影响在恢复到室温后会部分恢复。随后通过不同加载倾斜角（加载方向与泥岩层理间的夹角）条件下的直剪试验，结合电镜扫描和三维激光扫描等细观结构观测技术，研究揭示了温度影响下，具有薄层理构造的各向异性泥岩损伤演化和变形破坏的物理机制。平行层理面方向的抗剪强度要低于垂直层理面方向的抗剪强度，并且剪切破坏面更加平缓光滑。在30~200℃范围内，热处理对泥岩的影响以水分蒸发和矿物膨胀为主，增强了矿物颗粒之间的摩擦性，从而提高了泥岩的抗剪强度参数。这种效果在层理内比在层理间表现更为明显，因此温度升高也进一步增强了泥岩力学性质的各向异性。基于所建立的能够反映软岩薄层理构造特征的横观各向同性本构模型，对隧洞开挖支护及长期蠕变进行了数值模拟，围岩与支护结构的应力分布和变形很大程度上受水平构造应力和岩层产状影响，软岩蠕变导致洞周围岩应力松弛，支护结构相应承受更大荷载。通过对比分析不同支护方案的长期服役性能，在传统一衬和二衬之间添加轻质混凝土缓冲层有利于围岩变形及应力释放，可以作为优选的支护结构形式。本项研究的相关成果不仅为高放废物泥岩处置库的场址评价和概念设计提供关键参数和理论基础，也为其它各向异性岩石中的深部地下工程设计、施工提供了参考和技术支持。