Effect of salt vertical distribution on sulfate-affected soils deformation.

Sulfate heave caused by salt swelling behavior poses a threat to engineering safety. The salt vertical distribution has a significant impact on the salt swelling behavior of sulfate-affected soils. A series of laboratory tests were conducted to explore the law of salt swelling and deformation of sulfate-affected soils under different salt vertical distributions. The results indicated that the salt swelling deformation mainly occurred in the initial rising and falling temperature stage. Residual accumulation formed as the salt swelling deformation increased over cyclic times. Salt swelling deformation increased with the increase in water content and salt-water ratio. The salt swelling deformation of sulfate-affected soils with a decreasing salt vertical distribution was larger than the other two forms. The maximum salt swelling also decreased as the water content and salt-water ratio reduced. In the 15 % water content samples with the vertical distribution of salt decreasing with depth, the maximum decrements were 34.78 %, 70.43 %, and 85.10 % as the salt-water ratio reduced, respectively. The sulfate-affected soils with the gradually decreasing salt distribution formed a great radial expansible strain. However, the soil with uniform salt distribution had a larger contractive strain. While the contractible strain increased with the reduction in water content, the expansible strain dropped. This work reveals the law of salt swelling deformation under the effect of salt vertical distribution, providing an important reference for subgrade engineering in sulfate-affected soils.