Experimental study on salt frost heaving mechanical properties of fine-grained sulfate saline soil under freeze-thaw cycle conditions
Sulfate saline soil will produce the salt swelling phenomenon in the case of water loss or temperature reduction,which seriously affects the normal use of structures.In order to study the mechanical properties of salt frost heaving of fine-grained sulfate saline soil,the sulfate saline soil along the Ershilipu area of Qinghai Ledu highway section was selected,and the indoor freeze-thaw cycle test was carried out by using the self-made test box to analyze the effects of salt content and the number of freeze-thaw cycles on the normal salt-frost heave force.The experiment results show that during the freeze-thaw cycle,the salt solution in the soil migrates to the upper surface of the soil,and the salt crystals and ice crystals precipitated at the same time increase the concentration of sodium sulfate solution in the soil sample,thus causing the soil to expand and deform.The salt frost heaving force of fine-grained sulfate saline soil with compaction coefficient of 0.93 and water content of 20％increases with the increase of salt content and freeze-thaw cycles,and the growth trend of salt frost heaving force decreases with the increase of freeze-thaw cycles.In a freeze-thaw cycle,according to the law of salt expansion ratio and frost expansion ratio changing with temperature in salt frost heave force,the change of salt frost heave force is divided into four stages:salt expansion stage,salt frost heave coupling stage,frost heave stage and melting stage.The freezing temperature of fine-grained sulfate saline soil with a salt content of 1.5％～4.0％varies from 2～5 ℃,and the freezing temperature decreases with the increase of salt content.The freezing peak value and residual value of salt frost heave force increase with the increase of freeze-thaw cycles,indicating that the salt frost heave force of fine-grained sulfate saline soil is cumulative,and the greater the salt content,the stronger the accumulation.
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