Study On Mechanical Characteristics And Microscopic Mechanism Of Loess Under Water And Salt Action

Under the action of water seepage,salt enters the porous medium of the soil in the form of ions,which changes the structure and mechanical characteristics of the soil,which is called water-salt effect.In nature,there is some salt in the infiltration liquid of loess,and the inherent salt in loess makes the mechanical properties of loess more complicated due to the water-salt interaction.This article uses desalinated Q2 loess and quartz sand as the test materials,using different concentration gradients of NaCl and CaCl2 solutions,through variable head penetration test,confined compression test,uniaxial compression test,and cross plate shear test.Changes of mechanical properties such as permeability coefficient and strength of loess under water-salt effect.And through microscopic test methods such as scanning electron microscope test and nuclear magnetic resonance test,the microscopic mechanism of the change of soil mechanical characteristics under the action of water and salt and its influence on the mechanical properties of soil are explored.The main innovations and results of this research are as follows:(1)Considering that the clay and salt content of loess in various regions are quite different,and related researches still correspond to loess in a specific area,it is difficult to reveal the mechanics of loess with different texture and sand content under the action of water-salt.The study of characteristics provides a scientific basis.In this paper,desalinated Q2 loess and quartz sand are used as test materials,and the effects of water-salt interaction on the mechanical properties of sand loess are explored by adding quartz sand,and the test results are further expanded.It is found that the pore ratio,sand content and salt in the pore fluid of the soil have an effect on the permeability and strength of the loess.Under the action of water-salt,the permeability of loess increases and the strength decreases,but the salt concentration increases the permeability of the loess.Sex and strength have little effect.(2)At present,the microscopic research on the water-salt interaction in loess is very limited,and most of them are focused on the qualitative interpretation of the microstructure of loess.Analyze the changes in the microstructure of the soil,and use nuclear magnetic resonance technology to quantitatively evaluate the pore distribution and free water content of the soil under the action of water-salt.Nuclear magnetic resonance tests have found that the sand content of the soil and the salt in the pore fluid will change the pore distribution of loess.Under the action of salt,the large pore size distribution of the soil increases,which means that the permeability of the soil becomes stronger and the strength becomes weaker.And through the analysis of the T2 spectrum curve obtained in the nuclear magnetic resonance test,the free water content and the bound water content distribution of the soil under different conditions are obtained.It is found that when sand and pore fluid are mixed into the soil as a salt solution,the content of bound water in the soil decreases and the content of free water increases.NMR test results can explain the changes in soil mechanical properties from a quantitative perspective.(3)At present,the application range of the characterization formula for judging the change trend of the mechanical index of the soil under the action of water and salt is relatively small.In this paper,based on the relevant experimental data,using theoretical analysis and theoretical derivation methods,by using quartz powder-bentonite as an analog loess,the concept of clay void ratio(e_c)is established to study the undrained shear strength and permeability of loess under water-salt Characterization of coefficients.The formula for evaluating soil permeability coefficient and undrained shear strength with ec/e L as an index can simplify the acquisition process of index parameters,and has a good effect on the unified characterization of soil permeability coefficient and undrained shear strength under different pore liquids.And its extended application to the characterization of the permeability coefficient of loess under the action of salinity has also achieved good results.