Experimental Research On Salt Expansion Properties Of Sulfate Saline Soils Under One Time Decrease Of Water Content

Majorities of the researches on salt expansion properties of sulfate saline soils are experimental study on salt expansion under the variable temperature condition(single cooling,multiple freeze-thaw cycles).However,the actual conditions are usually complicated in saline soil area.The cyclic variation of soil moisture content,caused by rainfall,evaporation of surface water and rise and fall of the water table,is another important factor leading to the occurrence of salt expansion of sulfate saline soil.For example,in the wintering period of inland saline soil area,the characteristics of the climate shows that the ground temperature continues to decline,the amount of precipitation is very low and the evaporation is large(precipitation is in the form of snow and the depth of infiltration is very shallow).The ground(about 2~4m depth)shows the characteristics of single decline in moisture content and single cooling.Salt expansion occurs during the phenomenon.Obviously,salt expansion tests under multiple freeze-thaw cycles and single cooling has certain limitations for the salt expansion characteristics of sulfate saline soil.In order to explore salt expansion properties of sulfate saline soils under the one time decrease of water content,11 sets of indoor simulation tests under one time decrease of water content,lasting for 2868 hours,have been carried out using the self-developed experimental equipment.The following conclusions can be drawn:(1)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%,there is an approximate second-degree parabola correlation of the lower convex between salt expansion rate and salt content.The drying shrinkage rate of sulfate saline soil reaches the maximum 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.(2)The sensitive water content range of salt expansion,slightly influenced by salt content,is basically stable when salt content increases from 1.5% to 4.0%.(3)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 in the decrease of water content.Based on the above test results,4 sets of salt expansion tests have been carried out under single cooling.The main conclusions are as follows:(1)The temperature range beginning to swell of sulfate saline soil gradually goes up and the interval range of salt sensitive temperature range gradually expands with the increase in salt content.(2)The salt expansion rate under single cooling is higher than the salt expansion rate under one time decrease of water content.However,the difference between the salt expansion rate of the two test conditions is basically constant with the increase in salt content.It is expected to provide guidance for evaluation on the salt expansion of the foundations of residual sulfate saline soil with high salt content in the northwest region.