Investigation Of The Microstructure Effect On The Permeability And Mechanical Property Of Compacted Loess

With the implementation of the national strategy and initiatives of"Western Development"and"One Belt One Road",a large number of infrastructure projects have been carried out in the loess region.In the loess hill and valley regions,land resources are extremely limited and space available for urban development is limited due to the influences of topography and terrain.To overcome this limitation,a large number of projects in which the tops of mountains were removed to fill the valleys were unavoidable.This kind of deep excavation and high filling project inevitably caused many geotechnical engineering problems during the construction and operation of high filling area,such as excessive settlement deformation and slope instability,the occurrences of which were highly related to the permeability and mechanical property of the loess.Based on the loess high filling project in Yan’an new area,this paper systematically studied the microstructure,permeability,mechanical property of the loess materials in the filling area,analyzed the effects of initial dry density and water content on their permeability and mechanical property,and revealed the microscopic mechanism of permeability and mechanical property.The main content of this research is as follows:（1）The microstructure characteristics of compacted loess with different initial dry densities and water contents were investigated through mercury intrusion porosimetry（MIP）and scanning electron microscopy（SEM）tests.Based on the pore size distribution curve and mercury withdrawal curve obtained from MIP test,the pore size boundaries of the large,medium and small pore groups of compacted loess were determined as 2μm and 0.2μm,respectively.In combination with morphology of soil particles and pores observed by SEM test,it was thought that large pore groups corresponded to large pores between aggregates,small pore groups corresponded to small pores inside aggregate,and medium pore groups fell in between these two groups.The variations of the compacted loess structure with dry density and water content were analyzed.（2）The variation of saturated permeability coefficient of compacted loess with initial dry density and water content was studied by laboratory saturated permeability test,and the empirical relationship between the total porosity ratio,effective porosity ratio and saturated permeability coefficient was established.The influence mechanism of bound water content and dry density on saturated permeability coefficient of compacted loess was investigated.（3）The soil-water retention curves（SWRCs）of compacted loess with different dry densities in a wide suction range were measured using filter paper method.The SWRCwas divided into two parts with a suction boundary of s_d,namely s_min-s_dand s_d-10⁶k Pa.By fitting the SWRC using Fredlund&Xing model,the unsaturated permeability coefficient of compacted loess was determined.（4）Through high pressure consolidation and direct shear tests,the variations of compression parameters and strength indexes of compacted loess with the initial dry density and water content were analyzed,and the empirical formula for estimating compression parameters and shear strength indexes of compacted loess based on initial dry density and moisture content was established.（5）Based on the pore size distribution curve and SWRC and in combination with SEM microstructure images,the influencing mechanisms of initial dry density and water content on permeability and mechanical property of compacted loess were revealed.