Study On The Structure Of Soft Plastic Loess Under Wet-Dry Cycle

The structure of loess is formed by the interconnection of soil particles and pores through cemented substances,which is the sum of the particle arrangement,particle connection,and pore distribution,and could reflect the arrangement and connection of loess particles and pore size characteristics such as number,quantity and so on.The climate of the Loess Plateau is arid,precipitation is the main source of groundwater supply,the natural environment is susceptible to a state of wet-dry cycles,and soft plastic loess happens to be located in the aquifer position,thus engineering properties of soft plastic loess will follow changed during the period of wet-dry cycles of the natural environment,and changes in engineering properties of loess are structural issues ultimately.Therefore,research on the response of soft plastic loess structure to the effect of wet-dry cycle is helpful to reveal the structure characteristics of soft plastic loess under the effect of wet-dry cycle,and provide data and theoretical references for the operation and maintenance of soft plastic loess engineering buildings.In this article,soft plastic loess is taken as the research object.Firstly,samples are taken at different mileages of the project site,basic physical and chemical tests are conducted.Then,four initial water content which is 10%,15%,20%,25%respectively and 0,1,2,3 wet-dry cycle processes were set,the response of structural parameters to the effects of wet-dry cycle was mainly revealed while analyzing the compression deformation properties of soft plastic loess.Then,the response of the soil water characteristic curve to the wet-dry cycles was carried out,and based on this,a theoretical analysis of the pore size distribution characteristics was carried out.Finally,the microscopic scanning electron microscopy and physical adsorption test were carried out,the response of microstructure and pore size distribution of soft plastic loess to wet-dry cycle were analyzed,combining with the macro-structural characteristics,the response of Soft plastic loess structure to the effect of wet-dry cycle was discussed.Physical and chemical properties test results showed that:The water content,density,dry density,plastic limit and liquid limit of soft plastic loess are distributed respectively at the range of 25.6%-28.6%?1.91g/cm³-2.00g/cm³?1.48g/cm³-1.57 g/cm³?18%-21%?30%-34%;among the mineral components,the content of quartz is the highest,with a mass fraction of 51%-52%;in the particle size composition,the proportion of clay and powder content is higher than that of sand content;the main chemical components are Cl^-and Ca²⁺,with average contents of about 3.3 and 14.5,respectively.Compression deformation performance and structural parameter test results showed that:After the wet-dry cycle,the compressibility of Soft plastic loess is increased,and the larger the initial water content,the smaller the effect of wet-dry cycles on compressibility;under the same number of dry and wet cycles,the larger the initial water content,the smaller the structural parameters;under different wet-dry cycle numbers,the larger the initial water content,the smaller the sensitivity to the increase in the number of wet-dry cycles.Soil water characteristic curve and pore structure test results showed that:With the increase of the number of wet-dry cycles,the soil-water characteristic curve of Soft plastic loess has a tendency to lean to the lower left,and the water holding performance continued to decrease.However,the soil-water characteristic curves after 2 wet-dry cycles is approximately coincide,and the matrix suction and water holding performance is basically stable,and it is predicted that with the increase of the number of wet-dry cycles,the small and medium pores in the Soft plastic loess will continue to decrease while the large pores will continue to increase,but the pore changes will not varied after2 wet-dry cycles.Micro test results showed that:The smaller the initial water content,the more dry and wet cycles are required to stabilize the microstructure and morphology;with the increase of wet-dry cycles,the number of pores in the soft plastic loess showed a steady decrease trend,while the apparent porosity showed an increase trend,and the smaller the initial water content,the more wet-dry cycles are required to slow the change trend;and under the same initial water content,from 0 to 3 wet-dry cycles,these three indicators showed an increasing trend.