Abstract: In order to explore salt expansion properties of sulfate saline soils under the decrease of water content, 11 sets of indoor simulation tests under one time decrease of water content, lasting for 2 868 hours, have been carried out using the self-developed experimental equipment. It is shown that the salt content of swelling initiation of sulfate saline soil is 1.2%. The volume of sulfate saline soil shrinks when the salt content of sulfate saline soil is less than 1.2%, and there is an approximate second-degree lower convex parabola correlation between salt expansion rate and salt content. The drying shrinkage rate of sulfate saline soil reaches the maximum value when the salt content is 0.5%. When the salt content is greater than or equal to 1.2%, the volume of sulfate saline soil swells. The salt expansion rate increases with the increase in salt content and there is a linear correlation between the two. The sensitive water content range of salt expansion, slightly influenced by salt content, is generally stable when salt content increases from 1.5% to 4.0%. It can also be concluded that the decrease rate of water content is negatively correlated with the salt content, and the decrease rate of water content in the same salt content decreases with the decrease of water content. Based on the above test results, 4 sets of salt expansion tests have been carried out under single cooling. It is shown that the temperature range initiating swelling of sulfate saline soil gradually goes up and the interval range of salt sensitive temperature range gradually expands with the increase in salt content. According to the test results from two kinds of test conditions, the salt expansion rate of single cooling is higher than the salt expansion rate of one time decrease of water content. However, the difference between the salt expansion rate of the two testing conditions is basically constant with the increase in salt content. It is expected to provide guidance for evaluation on salt expansion of the foundations of residual sulfate saline soil with high salt content in the northwest region of China.

Key words: sulfate saline soil, salt expansion, drying shrinkage, water content, one time decrease, single cooling