Effect of Temperature on Swelling Characteristics of Bentonite-Sand Mixtures

High temperatures are caused by radioactive decay during the operation of the geological disposal of high-level nuclear waste. Therefore, investigation of the swelling characteristics of compacted bentonite and its sand mixtures is of considerable importance in assessing the performance of the artificial engineering barrier system in the repository. Swelling tests were carried out on Gaomiaozi (GMZ01) bentonite and its sand mixtures containing 70% and 30% bentonite at variety of temperatures 25, 60, and 90 ℃. The results show that there is a linear relationship between montmorillonite expansion coefficient and temperature (K-T_c) for osmotic expansion, and the maximum expansion strain increases with increasing temperature. The volume deformation of the mixture with high bentonite content at the same temperature can be expressed by the e_m-σ_v fractal relationship, and the bentonite surface fractal dimension is not affected by temperature when immersed within deionized water; the presence of sand skeleton in the mixture with low bentonite content, e_m will deviate from the e_m-σ_v curve when the overlying stress exceeds the stress threshold of the specimen. Combined with the fractal model, a calculation method is proposed to predict the expansion deformation of bentonite-sand mixtures with different sand ratios at different temperatures.