An improved heat-water–vapor-salt based salt swelling model for unsaturated sulfate saline soil under cooling

The salt swelling destruction in arid sulfate saline soil areas represents a severe problem in road, railway, and foundation engineering. It is imperative to explore a potential solution to solve the salt swelling for the sulfate saline soil. However, vaporous water has a large effect on the forms of sodium sulfate present in the soil, which has not been taken into account by existing models. This work proposes an improved heat-water-vapour-salt based salt swelling model by considering the vaporous water effect. Experiments on unsaturated saline soils were conducted to validate the accuracy of the model. Besides, the effects of temperature, water content, relative humidity, and solute concentration on salt swelling were reasonably analyzed. The results show that the salt swelling rate increases to 64% when the relative humidity reaches 60–90%; once the relative humidity exceeds 90%, the swelling rate will decline to 0%. Moreover, the salt swelling rate follows an upward convex curve along the relative humidity and decreases with increasing liquid water content. When the liquid water content is above 10%, the salt swelling rate is stable at around 0.3. Overall, the improved model is more accurate in predicting salt swelling than the existing model, which shows exceptional promise in providing useful insight into understanding the mechanism of salt swelling and the prevention of salt swelling in saline soils.