Volume change characteristic of compacted bentonite during hydration upon high suction change: Experimental study and constitutive simulation

The assessment and predicting of volume change characteristic in compacted bentonite during hydration upon high suction change are crucial considerations in the design and construction of geological repositories. However, the mechanism for volume change behavior of bentonite upon suction change path is not yet well understood. Existing elastoplastic models show some limitations for describing hydration deformation of compacted bentonite upon high suction change path. In this work, suction-controlled hydration deformation tests were conducted on compacted GMZ01 bentonite under constant vertical stresses. The various forms of void ratio-suction curves observed suggested that the swelling-collapse behavior during hydration was influenced by the over-consolidation ratio (OCR). Furthermore, it was observed that each hydration deformation curve (e-lns) exhibited a saturation suction value. When the suction decreased to the saturation suction, the bentonite reached a state where further hydration was no longer possible, resulting in the absence of additional swelling or collapse deformation. The unique relationship between saturation suction and stress applied, i.e. critical saturated state (CSS) curve was proved to existed, which dividing the stress space (s-p plane) into unsaturated and saturated zones. A model framework with the concept of CSS curve was introduced and the suction-induced volume change equation was determined based on the tests results. The simulation results of hydration deformation tests demonstrated excellent agreement with the experimental data. The test results in this work provide the important mechanical parameters for the design and construction of geological repositories. Meanwhile, the proposed model could describe volume change characteristic of compacted bentonite during hydration upon high suction change, showing great significance for the safety assessment of repositories.