盐溶液中膨润土的剪切强度理论及其试验验证研究

Deep repositories of high-level radioactive waste (HLRW) are foreseen to be excavated well below the groundwater table in suitable natural rock formations. Engineered barriers will be subjected to a number of nontypical environmental stresses including high temperature, changing groundwater chemistry, varying air pressure and varying crustal stresses. In the most critical situation, high-salinity water may inhibit the mechanical capacity of the material to compromise the safety of the repository. The study of the shear strength of bentonite in saline solution is still scare. In this project, the mechanism of the reduction in shear strength is revealed based on the surface fractal model for bentonite under changing groundwater chemistry, varying air pressure and varying stresses. The effects of groundwater chemistry are expressed by ostomic suction, and the matric suction is calculsted from the air pressure. The modified effective stress is proposed by the coupling of osmotic suction, matric suction and crustal stress. The shear strength of bentonite in saline solution is expressed by the modified effective stress firstly proposed in this project. The triaxial compression tests are performed under high pressure using the modified triaxial apparatus with the saline concentration controlling system. This project is an academic innovation in geological engineering, and has a large practical significance. The research results of this project can be widely applied to the design, construction and maintenance of the bentonite buffer in nuclear waste repository.

作为高放废物深层地质处置库工程屏障的膨润土缓冲/回填层，受到高温、地下水化学、高地应力和高气压影响，导致膨润土膨胀能力丧失、剪切强度下降，危及高放废物地质处置库的安全。目前有关地下水化学对膨润土剪切强度影响的研究成果很少，本项目基于膨润土表面的分形模型，揭示地下水化学、高地应力和气体压力对膨润土剪切强度影响的机理；采用渗透吸力表示水溶液化学作用的影响，根据气体压力计算基质吸力，提出考虑渗透吸力、基质吸力和地应力耦合的修正有效应力公式，建立盐溶液中膨润土的剪切强度理论。采利用改装的高压三轴仪进行不同浓度盐溶液的膨润土剪切试验，验证盐溶液中膨润土的剪切强度理论。本项目既是工程地质的基础理论研究，又解决地质工程的实际问题，不仅具有创新的理论意义，也具有保护环境、造福子孙的社会意义和经济价值，研究成果可应用于保障高放废物处置库安全。

我国高放废物处置库建设还处于选址和实验室建设阶段，当前深入分析膨润土缓冲/回填层在地下复杂环境中的力学性能十分必要，研究膨润土在盐溶液中的剪切强度理论对于高放废物处置库工程屏障的设计和施工均具有举足轻重的作用。本项目基于申请者对膨润土分形结构的研究成果，将室内试验与理论研究相结合，针对高放废物地质处置库环境的特点，从膨润土微观结构特性出发，研究化学作用和温度对膨润土剪切强度的影响机理，揭示地下水化学、气体和地应力对膨润土剪切强度的影响，建立高放废物地质处置库环境中膨润土的剪切强度理论，探究高放废物地质处置库膨润土缓冲/回填层的破坏模式。本项目既是对工程地质基础理论的补充，也为解决实际重大工程问题提供理论支撑；既具有理论创新意义，也具有工程实用价值，研究成果具有广阔的应用前景。