Influence Of Alkali Pollution On Physical And Mechanical Properties Of Red Clay And Expansive Soil

China’s industrialization process has brought great soil pollution to the environment.At present,it is very important to study the physical and mechanical properties and engineering characteristics of contaminated soil for practical projects.In this paper,the physical properties,mechanical properties and micro-morphology of red clay and expansive soil before and after being polluted by Na OH are studied and discussed.The main work and research contents are as follows:(1)Referring to the existing preparation method of alkali-contaminated soil,Na OH crystals are used as pollutants,the initial water content of soil samples is controlled at 28%,and the concentration of contaminated liquid is controlled at 0%,1%,2%and 4%.The basic property index and mineral composition of red clay and expansive soil samples used in the test were measured.(2)The physical properties of red clay and expansive soil before and after pollution were tested,and the variation laws of liquid-plastic limit,clay content,specific gravity and specific surface area of polluted soil samples were obtained in turn.It was found that the variation trends between the two soils were basically the same,but the variation effects were different.This is mainly because expansive soil is affected by its own expansive characteristics.Under the erosion of Na~+,chemical corrosion and positive and negative charges play an obvious role,resulting in particle breakage and particle transformation effects,resulting in different effects of Na+on the physical properties of red clay and expansive soil.(3)The mechanical properties of red clay and expansive soil under alkali pollution were studied by direct shear test and indoor shrinkage test.The test data show that the cohesion,linear shrinkage and shrinkage coefficient of the polluted red clay and expansive soil increase and the friction angle decreases.Alkali pollution reduces the strength of soil and increases the vertical deformation,which is due to the dissolution of cement in soil,the collapse of micropores and the destruction of the soil skeleton of clay.Because of the different mineral composition,it is considered that alkali liquor mainly affects amorphous iron oxide in red clay,while in expansive soil it affects the interlayer lattice distance of montmorillonite.The test results show that the mechanical properties of expansive soil are stronger than those of red clay.(4)In order to better explain the macroscopic physical and mechanical change mechanism of red clay and expansive soil,micro-characterization test XRD diffraction test and scanning electron microscope test were used to explain that the clay mineral content of the two soils decreased,and expansive soil was obvious,and the connection mode between soil particles also changed.Red clay changed from broken particles to honeycomb structure,while expansive soil changed from flaky broken particles to layered aggregates,which was mainly caused by the chemical interaction between ions and the change of mineral composition activity.From micro to macro,it is more systematic and comprehensive to study the influence of alkali pollution on the physical and mechanical properties of red clay and expansive soil.