Effect of temperature on swelling behaviors of compacted bentonite in an annular technological void

To investigate the swelling behavior of compacted bentonite with a technological void and its microstructure evolution under the influence of different temperature, swelling pressure test was conducted on compacted bentonite in a annular technological void at different temperatures. After the closing of technological void, water content, dry density and microstructures was determined respectively. Results shows that the swelling pressure time-history curves shows a single-peak type that first increases to the peak and then falls down and eventually stabilizes. The dynamic equilibrium of the “wedge” force, formed by the thickening of bound water film, laminar cleavage, pore collapse and diffusion double layers thickening, dominates the evolution of the force state of bentonite from the vertical lateral limit to the constant volume. The law of increasing water content and decreasing dry density from the interior to the exterior was enhanced at high temperatures. The increase in montmorillonite expansive coefficient and water molecule diffusive coefficient with temperature enhanced the hydration and swelling behavior, and more inter-assemblage pores were occupied by the swollen montmorillonite. The entry of more water molecules into the montmorillonite interlayers at higher temperatures induced a higher degree of hydration reaction, lamellar cleavage, and pore collapse, which reduced the total void ratio and enhanced the swelling properties of bentonite. The research results can provide a scientific basis for analyzing the thermal-hydro-force coupling behavior of barrier materials, and provide a useful reference for the design and construction of bentonite engineering barriers in deep geological disposal reservoirs in China.