热-水-力共同作用下非饱和压实膨润土的宏微观行为研究

This project focuses on the macroscopic and microscopic thermo-hydro-mechanical behaviour of GMZ bentonite, which has been selected as the candidate Chinese buffer/backfill material of the geological repository of HLW. A series of macroscopic tests, including swelling tests, water retention tests, suction-controlled oedometer tests, unsaturated permeability tests, etc., will be conducted at different temperatures using several self-developed apparatus, which has been specially designed for bentonite tests and has the capacity of the application in high temperature. Microstructure evolution in the above macroscopic tests will be investigated systematically and quantitatively using mercury intrusion porosimetry (MIP) and environmental scanning electron microscopy (ESEM). Based on test results, a microstructure model will be proposed to describe the microporosity evolution with suction, stress and temperature. Utilizing the microstructure model, a series of microstructurally based hydraulic and mechanical constitutive models will be developed based on existing and well-evaluated macroscopic models, and will be incorporated into the finite element code developed previously by the applicant for the coupled thermo-hydro-mechanical analysis of unsaturated soil. The research results of this project can be utilized not noly to analyse the complex macroscopic behaviour of unsaturated bentonite using quantitative information of microstructure alteration, but also to predict the microstructure state of bentonite in the real geological repository condition. It is expected that understanding of buffer/backfill material will improved in both macroscopic and microscopic sense through this project.

本项目结合我国高放废物地质处置研发的实际工程需求，以我国处置库首选缓冲/回填材料高庙子膨润土为对象，拟对其在热、水、力共同作用下的宏微观行为开展系统的试验与理论研究。在宏观试验方面，利用自主研发的系列膨润土高温试验设备，开展不同温度下的膨胀、非饱和固结、持水、非饱和渗水/渗气等试验；在微观试验方面，以压汞分析与环境扫描电镜为手段，研究宏、微观孔隙在不同热-水-力作用路径下的变化规律。根据宏微观试验结果，建立热-水-力共同作用下微观孔隙演化模型；基于所建立的微观演化模型，构建考虑微观结构变化的非饱和持水、渗透及变形本构方程，并将其融入申请人已建立的热-水-力多场耦合数值模型及程序加以应用。本项目研究成果不仅可分析非饱和膨润土微观结构变化引起的复杂宏观行为，并且能用于预测实际地质库热-水-力耦合条件下非饱和膨润土中的微观结构变化，有助于深化对膨润土在处置库中的实际工作性能与安全状态的认识。

在高水平放射性废物地质处置库中，受到热、水、力的共同作用，作为缓冲/回填材料的压实膨润土会经历复杂的宏微观变化。本项目以我国高水平放射性废物处置库首选缓冲/回填材料高庙子膨润土为对象，开展了不同温度下的三向膨胀力特性、不同温度下的膨胀变形特性、不同温度下的非饱和压缩特性、温度循环变化下的持水特性、考虑Klinkenberg效应的非饱和渗气特性、不同温度下的渗水特性、热-水-力共同作用下的微观结构变化特征、考虑微观结构的非饱和热-水-力多场耦合模型等方面研究。研究结果表明：（1）膨胀力均与干密度大致呈指数关系；温度升高会引起膨胀力减小；膨胀力的各向异性与干密度、温度均无显著的相关性，水平膨胀力约为竖向膨胀力的90%。（2）随着温度、荷载增大，膨胀变形时程曲线的“双S型”特征愈加显著，且与最大膨胀变形量具有良好的相关性；膨胀变形与竖向荷载之间大致呈对数函数关系，且在半对数坐标中各温度下的关系曲线大致平行；在相同竖向荷载下，膨胀变形随温度升高大致呈线性减小。（3）温度升高会导致非饱和屈服应力的降低，但对非饱和变形系数基本没有影响。（4）持水能力随温度升高而下降，且含水率越高，温度影响越显著；在温度循环变化过程中吸力呈现出滞后性。（5）当渗气系数小于1.0E-14 m2时，压实膨润土中的Klinkenberg效应较为显著；气体滑脱因子随Klinkenberg渗气系数与体积含气率之比的变化满足幂函数关系；Klinkenberg渗气系数与体积含气率在双对数坐标中呈线性关系，且其斜率与含水率基本无关。（6）渗水系数随温度的升高有所增大。（7）膨胀前后发生显著的微观结构变化；膨胀前后团粒间孔隙比改变量，与竖向荷载之间满足对数函数关系，且随温度升高大致呈线性减小；膨胀前后团粒内孔隙比改变量基本不随竖向荷载、温度而变化。（8）通过区分团粒间孔隙与团粒内孔隙对力学、渗透、持水等的不同贡献，构建了考虑微观结构的多场耦合模型，并进行了初步的应用。