Abstract：The volume change of the buffer/backfill materials in geological repositories is affected by several factors during the long-term operations. For example，the variation of ion concentration in groundwater caused by the fluctuation of groundwater level and temperature，the variation of additional stress caused by the changing geological tectonic activity and geological environmental，and the backpressure from the restriction of surrounding rock and waste container. To simulate the volume change of the buffer/backfill materials affected by above-mentioned factors，a serial of swell-compression-rebound tests have been conducted on as-prepared compacted bentonite specimens with initial dry density of 1.6 g/cm3 using high-pressure consolidometer. Deionized water and NaCl solutions with different degrees of concentration were used as infiltration solutions. And these tests were performed under different chemo-mechanical stress paths. The volume change behaviours of the compacted bentonites under coupled chemo-mechanical conditions in these tests were systematically analyzed from the macro and micro perspectives. The results show that the final swelling strain and compression index of bentonite samples decrease with increasing NaCl solution concentration. By comparing the volume change behaviours of samples underwent desalination-salinization cycle with those did not undergo this cycle，it is found that the plastic behaviour of macrostructure is irreversible，while microstructural behaviour is reversible. For the samples under the desalinization cycle，with the increase of solution concentration and decrease of vertical stress，the final cycle swelling strain increases.
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2019, Vol. 38 
