Research On Regional Variation Of Three-dimensional Microstructure Of Loess In The Loess Plateau

Taking the Loess Plateau as the research area,this paper selected the Malan loess in16 areas such as Bailu tableland and Baiyin in the Loess Plateau region and the loess strata L₁,S₁,L₂,S₂,L₆,L₇,L₈ and L₉ in Luochuan.Through field investigations and related experiments,the basic physical and mechanical properties and microstructure characteristics of loess in the Loess Plateau are basically mastered,and then the three-dimensional microstructure model and quantitative index parameters are established,and the distribution characteristics and regional variation characters of three-dimensional microstructure of loess in the Loess Plateau are studied.The following achievements were obtained in this paper.(1)Based on the microstructure experiment,the three-dimensional microstru-cture quantitative index parameters of loess particle size,major and minor axis,sphericity,orientation distribution and its pore volume,pore size,throat size are established.The quantitative analysis of three-dimensional microstructure parameters of loess in the Loess Plateau is carried out.The results show that the three-dimensional microstructure parameters of loess in the Loess Plateau have specific probability density distribution characteristics.The probability density of particle equivalent diameter(Eq-Diameter)satisfies Rational distribution,and the probability density of sphericity satisfies Beta distribution,and the morphology ratio,pore equivalent radius(Eq-Radius)and throat channel length all Satisfy Gamma distribution,and throat equivalent radius satisfies Gaussian distribution.(2)The three-dimensional microstructure of Malan Loess in the Loess Plateau has obvious regional distribution character.1)The Malan loess in the northern part of the Loess Plateau contains more large particles,while the Malan loess in the southwest has more small particles.On the whole,the particle size shows a trend of gradually decreasing from north to south.2)The three-dimensional morphology types of Malan Loess particles are mainly thin-slice,long-strip,multi-angular,sub-angular,sub-spherical and spherical.On the whole,most of them are sub-angular,followed by sub-spherical.3)In the belt of Shuozhuo-Lvliang-Yan'an-Qingyang-Longxian-Tianshui on the Loess Plateau,the particles are approximately vertical and tend to distribute in the northeast direction,while in the northwest of the Loess Plateau,the particles tend to distribute in the northwest direction.4)The regional variation character of pore Eq-Radius,throat Eq-Radius and throat Channel length is closely related to the loess particle Eq-Diameter and its regional variation character,showing a decreasing trend from north to south gradually.5)The microstructure of Malan loess can be divided into three types:single-particle aerial structure,aggregated-particles aerial structure and flocculation structure.Moving from the north of Loess Plateau to the south,the three structures show the characteristics of gradual decrease,first increase and then decrease,gradual increase one by one.(3)The three-dimensional microstructure of loess in different strata of Luochuan has obvious regional distribution character.1)With the increase of the strata depth,the particles size,pores and throats size gradually increase,while the sphericity and the morphology ratio gradually decrease.The results show that the material sources of each strata are basically the same,but the environment in the strata process is different.2)In L₁-L₉ strata,the Phi angle and Theta angle of the particles have basically the same changing trends.The loess particles in the deeper strata are not easy to deposit vertically,but tend to deposit gently or horizontally,and most of the particles in each strata are distributed in northeast direction.3)The physical properties of loess in Luochuan are closely related to its microstructure parameters.In L₁-L₉ strata,loess density and the mode of its equivalent diameter all become larger generally with the increase of strata depth,showing a positive correlation;the liquid-plastic limit has a negative correlation with the mode of morphology ratio of particles;the permeability coefficient has a negative correlation with the mode of pore Eq-Radius,throat Eq-Radius and throat channel length.