Coupled Thermo–Hydro–Mechanical Characteristics of Compacted GMZ Bentonite: Parameters Identification and Validation

Abstract

Compacted Gaomiaozi (GMZ) bentonite has been considered as the first choice of buffer materials in the deep geological disposal of high-level radioactive wastes (HLW) in China. During the long-term lifespan of the repository, the bentonite barriers will simultaneously undergo a coupled thermohydromechanical (T-H-M) process, which induces complex volume changes. In this study, the constitutive model of GMZ bentonite with consideration of THM coupling was established, using the framework of the BExM model along with a thermal volume change model for unsaturated soils. New formulations for the interaction between micro and macrostructures (fI and fD) and the thermal loading yield surface (TY curve) were adopted. Emphasis was placed on the identification and validation of the material parameters based on a series of experimental results. A comparison between the simulated and measured values show that the improved model with parameters calibrated successfully represents the main features of volume changes observed in the laboratory and during wetting-drying cycles, elastic thermal expansion, and plastic thermal contraction under various suctions and stresses, as well as compressibility under various suctions and temperatures.