Effect Of Wood Ash On Slope Mechanical Stability Of Sandy Subgrade

Wind-blown sand disaster is the main reason for the low stability of subgrade slope of sand-crossing highway in Mu Us desert.Sand shrubs are planted on both sides of the road to prevent wind and fix sand.Because sammophytic shrubs are not easy to be planted and grow slowly,plant ash is often used to fertilize them to accelerate plant growth and development.In this thesis,the author studied the impact of wood ash content on the mechanical stability and microstructure of sand-crossing highway in Mu Us desert slopes,aiming at providing a basis for the application of wood ash in roadbed slopes.This paper takes the sandy soil at the top,middle,and bottom of the slope at the junction of National Highway G338 and Provincial Highway S215 as the research object,and shear damage as the research background.Firstly,it starts from the soil body physical properties experiment,the particle gradation characteristics and natural dry density of the sandy soil under different slopes are studied;Secondly,the influence of various amounts of wood ash admixture on the heavy compaction characteristics is studied by compaction test;then,the influence of the quantity of wood ash(5%,10%,15%,20%)and stress conditions(50,100,200,300 k Pa)on shear mechanical properties of wood ash mixed with sandy soil is investigated by direct shear test;Finally,the influence of wood ash content on the microstructure and pore characteristics of compacted soil and its formation mechanism are explored by scanning electron microscope.This study can provide a basis for the engineering application of wood ash in roadbed slopes.The main research contents and results are as follows:(1)Wood ash can increase the maximum dry density under the optimum moisture content of its mixed sand.(2)The peak shear stress or horizontal displacement of the sand soil in the slope to the due shear stress are all larger than that of the sand soil on the top and bottom of the slope under the same vertical pressure.The effect of vegetation ash on the internal friction angle of mixed sandy soil on each slope is small,which shows a wavy line,and the increase or decrease of the internal friction angle is about 10% compared with that of plain soil.When the content of vegetation ash is about 15%～20%,the cohesion and shear strength of the mixed sand soil increase obviously.When the content of vegetation ash is15%,the cohesion of the mixed sand soil increases most.When the content of plant ash is 15% and stress is 200 k Pa,the shear strength can be improved greatly.(3)The SEM microscopic images of the specimens with different amounts of wood ash are obtained by scanning electron microscopy,and it is observed that the microstructure of the mixed sand soil is mainly "skeletal",and the wood ash particles fill the pores between the sand grains,reduces the proportion of small and medium pores,and effectively changes the pore size and particle size in the mixed sand soil.The rise of wood ash particles not only leads to the increase of the proportion of large pores,but also strengthens the breathability and permeability of soil.