Compacted bentonite–sand mixture is proposed widely as backfill in geological repositories for disposal of radioactive waste in many countries because this material has significant swelling capacity and low water permeability. Development of the swelling pressure of backfills upon hydration is related closely to the stability of the host rock in the geological repository. No systematic experimental studies have been carried out to explore the effect of a water phase on the swelling pressure and water retention of bentonite–sand mixtures with insignificant osmotic suction. The objective of the current study was to examine experimentally the influence of a water phase involving liquid water and water vapor on swelling pressure and water retention of a bentonite–sand mixture with insignificant osmotic suction. Swelling-pressure tests with suction control and water-retention measurements under constant-volume conditions were performed on the compacted bentonite–sand mixture with a dry density of 1.80 g/cm³. Osmotic and vapor equilibrium techniques were used to make identical specimens adsorb liquid water and water vapor, respectively. The experimental results showed that the water phase had almost no effect on the swelling-pressure patterns of the unsaturated bentonite–sand mixture upon hydration over a suction range from 27 to 3 MPa. The swelling pressure increased significantly with decreasing suction from 27 to 3 MPa, regardless of the mixture adsorbing either the liquid water or water vapor. Nevertheless, the water phase had a considerable impact on both the swelling pressure and water retention of the unsaturated bentonite–sand mixture upon hydration over the same suction range. For a given value of suction in the range above, the swelling pressure and the water content of the bentonite–sand upon adsorption of liquid water were greater than those upon adsorption of water vapor. The influence of the water phase on the swelling pressure and the water retention of the bentonite–sand mixture with insignificant osmotic suction is related mainly to the hydration or swelling mechanism of Ca-rich bentonite.

由于压实膨润土砂混合物具有显着的膨胀能力和低透水性，因此许多国家广泛建议将其作为放射性废物处置地质处置库的回填材料。充填体水化膨胀压力的发展与地质处置库中母岩的稳定性密切相关。尚未进行系统的实验研究来探讨水相对渗透吸力微弱的膨润土-砂混合物的膨胀压力和保水性的影响。本研究的目的是通过实验检验包含液态水和水蒸气的水相对渗透吸力微不足道的膨润土-砂混合物的膨胀压力和保水性的影响。对干密度为 1.80 g/cm ³的压实膨润土-砂混合物进行吸力控制膨胀压力测试和定容条件下的保水性测量。使用渗透和蒸汽平衡技术使相同的样品分别吸附液态水和水蒸气。实验结果表明，在 27 至 3 MPa 的吸力范围内，水相对不饱和膨润土-砂混合物水合时的膨胀压力模式几乎没有影响。无论混合物吸附液态水还是水蒸气，随着吸力从 27 MPa 降低至 3 MPa，膨胀压力显着增加。然而，在相同吸力范围内水合时，水相对不饱和膨润土-砂混合物的膨胀压力和保水性有相当大的影响。对于给定的吸力值在上述范围内，膨润土砂吸附液态水时的膨胀压力和含水量大于吸附水蒸气时的膨胀压力和含水量。水相对渗透吸力较小的膨润土-砂混合物的膨胀压力和保水性的影响主要与富钙膨润土的水化或膨胀机制有关。