Microscopic Scale Study On Soil-water Characteristics Of Unsaturated Anisotropic Silty Sand

Soil-water characteristics are one of the core problems in the study of unsaturated soils,and pore structure is an intrinsic indicator reflecting changes in physical and mechanical properties of soils.In this paper,high-resolution micro-CT is used to perform three-dimensional scanning imaging of Nanjing silty-fine sand samples with different water content under water loss conditions.By means of simulating dynamic scanning,the scanning images of Nanjing silty-fine sand in dry state,saturated state and with mass moisture content of 30%,25%,20%,15%,10%,5%and 0%were obtained.And the soil sample matrix suction was measured and Permeability is obtained by the lattice Boltzmann method.The following conclusions were obtained:(1)During the process of adding water to the saturated state and then gradually losing water,the pores of the Nanjing silty-fine sand are gradually shrinking due to the suction of the matrix,and the shrinkage phenomenon is gradually weakened.The direction of the pore shrinkage displacement is mainly downward and inward displacement,and the overall displacement of the pores The change was small and the maximum displacement of the pores was 591.5 ?m.There is a large displacement in the boundary pores,and a block-type concentrated displacement phenomenon occurs in other parts,and the overall distribution of the block-type concentrated displacement is relatively uniform.And,the pore structure parameters fluctuated slightly under different water content conditions.(2)When the water is saturated,the soil sample shrinks obviously and appears the center of shrinkage,and the displacement of the shrinkage center is small.At the same time,the shrinkage effect makes the soil pore throat smaller,the connectivity worse,and the porosity,coordination number,average pore volume,average pore radius,average throat radius and throat length decrease,The number of pores increases.In addition,duing to the degree of anisotropy of the matrix suction,the volume shrinkage of some pores and throats is reduced,and the volume of some pores and throats is increased,resulting in larger pores and throats,resulting in maximum pore volume and maximum pore volume,Radius,aperture variance,maximum throat radius,and pore throat ratio increase.At the same time,the typical small pores evolved into large pores,and the morphological features changed significantly.The pores increased significantly and the shape became regular.(3)During the process of losing water from saturation to a water content of 20%,the matrix suction is small,the soil sample shrinkage is not obvious,and the pore displacement is small.(4)When the water content is 20%dehydration to 10%,it exhibits a more obvious contraction state under the action of larger matrix suction,and the pore displacement is relatively large.(5)When the soil sample loses water from the state of water content of 10%to the moisture content of 0%,the larger matrix suction makes the soil sample shrink obviously,the pore displacement is larger,and the shrinkage center appears at the same time.(6)The influence of pore structure parameters on the permeability of Nanjing silty sand is ranked from the largest to the smallest:average throat radius,average pore radius,throat length,porosity,average pore volume,pore throat coordination number,maximum pore radius,and throat.The cross-sectional area shape factor,the maximum throat radius,the aperture variance,the porethroat ratio,the number of pores,the pore cross-sectional shape factor,and the maximum pore volume.