Deformation properties of coarse-grained sulfate saline soil under the freeze-thaw-precipitation cycle

Salt expansion deformation is the main engineering hazard of saline soil, which restricts the application of coarse-grained sulfate or sulfite soil as roadbed filling. The main factors affecting salt expansion deformation are change of salt, water and temperature. The principal research objectives of this paper is to offer a basic data reference for the structural design of coarse-grained sulfate saline soil roadbed. To investigate the deformation properties of coarse-grained sulfate saline soil under the freeze-thaw-precipitation cycles, the large-scale sample experiments under the freeze-thaw-precipitation cycles and the freeze-thaw cycles were carried out with self-designed experiment equipment. The results showed that under the same freeze-thaw-precipitation cycles experiment conditions, the minimum temperatures of these samples with 1.5% and 3.0% soluble salt contents at a depth of 20 cm were 3.32 °C and 3.56 °C, respectively. In addition, it took less time for the lower salt content (1.5%) sample to reach the same low temperature compared to the higher salt content sample (3.0%). However, after seven freeze-thaw-precipitation cycles, it was shown that deformation of the sample with 1.5% soluble salt content was 32% higher than that with 3.0% soluble salt content. The maximum deformation amount of the coarse-grained sulfate saline soil after repeated freeze-thaw-precipitation cycles experiment was approximately 1.9–9.4 times larger than that after repeated freeze-thaw cycles experiment, which indicated that precipitation had a serious impact on the deformation of the sample. However, there was almost no difference between the lower salt content and higher salt content samples in the residual deformation caused by the cumulative effect of salt expansion in each cycle. Furthermore, the results showed that under the influence of precipitation, a high-level soluble salt content did not necessarily promote expansion deformation of coarse-grained sulfate soil. Water, salt, and temperature have complex coupling effects.