Study On The Loess Microstructure In Jingyang Xiushidu Profile

This paper relies on the project of national natural science foundation of China"reconstructing the law and mechanism of loess permeability change",taking the loess section of the south Jingyang Plateau in ShaanXi province?Xiushiduadu Village?as the research object,this paper started with the research methods of macroscopic mechanics and microstructure.By usingMastersize-2000 laser particle size analyzer and GUANTA-200Environmental Scanning Electron Microscope and other instruments,systematic study of the grain size composition,microstructure characteristics and physical properties of loess in Xiushidu section.Combined with the distribution law of loess granularity and the basic physical properties measured by laboratory geotechnical tests,the structural characteristics and pore distribution of the loess were analyzed in detail,and the law of the microstructure change with depth was obtainedThe main conclusions are as follows:?1?According the results of particle size analysis of loess particles,the composition of loess is mainly composed of coarse silt,followed by clay,in which the coarse silt content in loess layer was 53.23%,while the coarse silt content in paleosol layer was 45.25%,the content of clay in ancient soil layer is more than loess layer,and the clay content increases with depth.the microstructure of the soil was observed and photographed by ESEM,and the skeleton shape,structure type,cementation form and pore characteristics of the soil were described.?2?By analyzing the microstructure images of the whole section loess,the description and analysis of the basic unit element,contact mode,and cementation type of the skeleton particles were analyzed.The variation of microstructure characteristics of loess with depth were summarized.The basic unit element in loess microstructuren composite can be sumed up as granular unit and aggregated unit,other strata were composed of loess matrix particles in the form of their common existence,only L₁ and L₂ layers of loess skeleton particles are composed of coarse clastic elements.?3?The fluctuation amplitude of the type of soil structurewith the increase of the buried depth in the section decreases gradually,the structural type of the soil from thelishi loess was less fluctuating than the Malan loess.Moreover,the soil structure types of the loess-paleosoil contact zone are large and volatile.?4?The pore area ratio by using IPP6.0 image processing software and porosity were verified.Finally,the optimal magnification and threshold value of the microstructure image were determined respectively as the 800X andthe first number of the peak value of grayscale distribution curve respectively.According to the pore area ratio as a feature of the two-dimensional cross-section of the pore,the ratio of the pore area is taken as the main evaluation parameter in the microstructural study process.The pore area ratio of horizontal plane and vertical plane of soil sample is fitted with linear equation,the pore area ratio decreased with the increase of buried depth.?5?The horizontal plane and vertical plane of the loess were mainly micro-pores and small pores,In loess strata in the content of micro pore less than ancient micropore content in soil formation,with the increase of loess sample depth,the pore size and pore size decreased with the increase of buried depth.?6?By analyzing the fractal dimensions of the pores,the pore distribution of the soil tends to disperse with increasing depth.The lower the degree of collectivization,the smaller the distribution density and the more complicated the pores.