Gaomiaozi (GMZ) bentonite has been confirmed as the buffer material in the Chinese disposal program of high-level waste. To investigate the thermal volumetric behaviour of compacted GMZ bentonite, several stress paths were performed on the specimens presaturated with NaCl solutions to obtain the scheduled OCR and verticle stress. Then multi-step heating-cooling tests were conducted. Test results show that thermal volume change strongly depends on the vertical pressure, OCR and concentration of the presaturation solution. For the specimens presaturation with deionized water, heating induces contraction below the transition temperature and followed by dilation at normal consolidation state, while only induces dilation at overconsolidation state. A larger vertical pressure leads to a larger transition temperature. For the specimens presaturated with NaCl solutions, heating basically induces dilation. The specimens with large vertical pressure accumulate a total contraction after a thermal cycle. For a given concentration and verticle pressure, the specimens cumulate a larger irreversible dilation at higher OCR. The influence of salt solution is non-monotonic. The dilute solution and high saline solution significantly promote the thermal expansion of saturated GMZ bentonite during heating.
GMZ bentonite Thermal volumetric behaviour Salt solution Vertical pressure OCR
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The authors are grateful to the National Natural Science Foundation of China (41422207 & 41772279), China Atomic Energy Authority (1051) and Fundamental Research Funds for the Central Universities.
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