Experimental Study On The Influence Of Medium Dissolved Salt On The Strength Of Structural Loess

In recent years,the reconstruction projects after the demolition of the loess area have gradually increased,and there are many cases of external salt intrusion into the loess foundation.The importance of studying the influence of salt content on the strength of the soil is self-evident.In this paper,the original chemical plants,sewage plants and landfill plants were demolished and reconstructed as the engineering background,and the Q2 loess in Xi’an area was taken as the research object,and the research on the change of the strength of the loess caused by the change of the dissolved salt content was carried out.In the research of this subject,the medium-dissolved salt CaSO4 solution was used as the salt environment,and the scanning electron microscope test was used to analyze the meso-mechanism of the undisturbed loess samples with different contents of the dissolved salt.Compression test(RTC)analyzes the stress-strain relationship and peak strength.Based on the binary medium model,the strength criteria of structural loess containing intermediate dissolved salt under two stress path conditions are established respectively.The research content and results are as follows:(1)Using anhydrous CaSO4 as the salt solution environment,set up 4 kinds of solution gradients(0%,0.1%,0.2%and 0.5%)of the middle-dissolving salt solution,and vacuum-saturate the undisturbed loess in the 4 solution concentration environments.Scanning electron microscope test(SEM)was carried out on the undisturbed loess with different salt content.The influence of the dissolved salt content on the pores of the loess structure was analyzed from a meso-level perspective,and the influence of the salt content on the pore number and area of the undisturbed loess was analyzed in combination with the PCAS system.The content of intermediate soluble salt acts on the mesostructure of undisturbed loess for research.The analysis shows that with the increase of the soluble salt CaSO4 content,the number of pores on the surface of the undisturbed loess structure decreases,the proportion of pore area decreases,and the bonding material between soil particles increases.(2)The undisturbed loess with different CaSO4 content in soluble salt was subjected to triaxial consolidation and undrainage tests under different confining pressure conditions and conventional compression and reduced confining pressure compression.The test sets the confining pressure levels as 25kPa,50kPa,100kPa,200kPa and 400kPa,and the stress-strain relationship and peak strength of the sample are studied.The test results show that:a.In the CTC test,the shear soil in the confining pressure environment below 200kPa shows strain softening,and the shear soil in the 400kPa confining pressure environment shows strain hardening;in the RTC test,under the low confining pressure of 25kPa and 50kPa,The peak strength of structural loess is much lower than the deviator stress value of the soil under the conventional triaxial test in the same confining pressure environment,the shear soil under the confining pressure of 100kPa and 200kPa shows a strain softening phenomenon,and the shear soil in the 400kPa confining pressure environment The body showed obvious strain hardening phenomenon;b.Shear deformation of the soil sample found that under the same confining pressure condition,the CTC and RTC test soil samples have the same failure form,but the damage degree is different.In the environment of relatively low confining pressure(25kPa and 50kPa),the damage of the sample shows the shape of cracks,and the cracks of the RTC test soil sample are shallow;at 100kPa and 200kPa,the test soil sample damages obvious shear bands,and the confining pressure increases.When it reaches 400kPa,the failure form of the sample becomes swelling;c.According to the results of the triaxial test under the two stress path conditions,it is found that the peak strength of loess increases with the increase of the dissolved salt content in the soil.(3)Based on the theory of the binary medium model,the test results are used to study the shear resistance sharing rate of the undisturbed loess containing moderately soluble salts under conventional triaxial compression and triaxial confining pressure reduction conditions,and establish two stress paths in Xi’an area containing moderately soluble salts.The strength criterion of salt-structured loess provides a certain theoretical basis for the calculation of soil strength under similar working conditions.