Strength And Deformation Characteristics Of A Sandy Sulfate Saline Soil

Saline soils are widely distributed in Northwest China.Due to the large temperature difference between day and night in this area,the sodium sulfate in the saline soil is easy to crystallize and precipitate during the cooling process,resulting in salt swelling and deformation of the soil.Therefore,the disease of the salt expansion engineering of sulfate saline soil in northwest China is very prominent.The deformation of the soil salt expansion will cause uneven deformation of the roadbed,which poses a great threat to the safety of train operation.Based on the purpose of providing a basis for the prevention and control of saline soil engineering diseases,this paper aims at a typical saline silt soil in Northwest China to study the deformation and strength characteristics of saline soil under freeze-thaw cycles through laboratory experiments and the following main conclusions are drawn:(1)Based on the theoretical analysis of the crystallization law of sodium sulfate,the main indicators affecting its dissolution characteristics were obtained.The critical crystallization temperature of sodium sulfate increases with the increase of salt content and decreases with the increase of water content.(2)The shear tests were carried out under the same conditions with different moisture contents.After analyzing the indoor shear test data of the soil,it can be concluded that the strength properties deteriorate with increasing moisture content.As the moisture content increased to 9.5%,the shear strength decreased by an average of25%.With a further increase in moisture content to 11.5%,the shear strength also decreased by an average of 28%.(3)According to the results of the direct shear test,the influence of salt content on the strength characteristics is analyzed,and it can be concluded that the salt content only affects the cohesion and does not affect the internal friction angle without considering the effect of freeze-thaw cycles.As the salt content increases,the water does not meet the dissolution conditions.It turns out that excess salt crystallizes and forms cements between soil particles,increasing soil cohesion.(4)According to the research results of the effects of freeze-thaw cycles,we found that the salinity,water content and the number of freeze-thaw cycles had a greater impact on soil cohesion,but less on the angle of internal friction in the soil.According to the results of 1-2 freeze-thaw cycles,the cohesion of the soil decreases.After 4-8 freeze-thaw cycles,the strength properties of the soil samples increased and tended to stabilize.The maximum strength index corresponds to a soil with a moisture content of 7.5%.(5)The salt swelling deformation of saline soil increases with the increase of salt content.Freeze-thaw cycles can greatly exacerbate soil salinity deformation.After many freeze-thaw cycles,the saline body with a salt content of 5% can strain up to 35%.By revealing the important engineering properties such as strength and deformation characteristics of this typical saline silt soil,the obtained research results can provide important scientific support for the engineering application of saline soil in Northwest China and the prevention and control of salt damage.