Study On Water Salt Migration And Deformation Characteristics Of Sulfate Soil At Freeze-thaw Cycle

The climate in southern Xinjiang is dry,the degree of groundwater mineralization is high,it is a typical inland arid desert climate environment,widely distributed sulfate soil,the water salt migration and accumulation to the surface under the action of seasonal temperature changes,the phase change of the water and salt phase due to temperature change,so that the sulfate soil salt-frost heave deformation,causing major damage to the safety of the engineering structure,according to which the research on the migration and deformation characteristics of sulfate soil under the action of freeze-thaw cycle is carried out.Using the freeze-thaw cycle test system of water-salt temperature coupling,the freeze-thaw cycle test under the condition of anhydrous salt recharge,open system and closed system saline soil recharge was carried out for the artificial preparation of sulfate soil in Aral area,and the water-salt migration law and deformation characteristics of sulfate soil were analyzed,and engineering measures to block the migration of water and salt and prevent salt-frost heave deformation were proposed according to the construction needs of sulfate soil foundation engineering.The conclusions of the relevant research are as follows:(1)Matrix suction was used as an important parameter to measure water and salt migration,and the effects of different salt content,moisture content and temperature on matrix suction were studied.The results show that the matrix suction power at low temperature is greater than that of the substrate at positive temperature,and the moisture content is negatively correlated with the suction of saline soil substrate when the salt content is the same,and the test results show that when the temperature is-20 °C,the salt content of8% and the moisture content of 1% of saline soil matrix has the largest suction,which is 2600.49 k Pa.(2)The freeze-thaw cycle test of sulfate soil without anhydrous salt replenishment in the closed system showed that under the action of freeze-thaw cycle,the salt in sulfate soil accumulated on the surface with water migration;The deformation of soil increases first and then decreases with the increase of salt content,and the deformation of soil accumulates linearly with the increase of freeze-thaw cycles.The maximum deformation of sulfate soil with a salt content of 5% was 8.53 mm during the fifth freeze-thaw cycle.The test results of freeze-thaw cycle of sulfate soil replenished by saline soil in closed system show that the water and salt in the soil column migrate and accumulate from the saline soil area on the high temperature side to the non-saline soil area on the low temperature side under the action of freeze-thaw cycle,and the overall deformation of the soil column is affected by the change of salt content of the lower recharged sulfate soil,and the deformation is the largest at 1% salt content,which is-1.35 mm,and the deformation of the soil column is between-0.3 and-0.25 mm under the rest of the sulfate content.(3)The freeze-thaw cycle test of sulfate soil in the open system showed that the water salt migration and recharge intensity were the largest in the low-temperature freezing period,and the water migration was affected by the salt content of the recharge solution.The deformation of the soil is only 5%,the salt-frost heave deformation occurs,the maximum deformation is 0.2mm,the settlement value of the rest of the salt solution is lower than that of distilled water,and the sulfate solution replenishment has an effect on the soil deformation.(4)Through the comparative analysis of anhydrous salt recharge in closed system of saline soil with2% salt content,saline soil recharge in closed system and recharge with 2% saline solution with a concentration of 2% saline solution,the deformation was 1.24 mm,0.14 mm and 0.09 mm,respectively,that is,the deformation was sorted by size,respectively,the anhydrous salt recharge in the closed system> the open system > the saline soil recharge in the closed system,and the change trend of water and salt migration was consistent with the deformation change.