Experimental Study Of Permeability Characteristics Of Modified Loess

Loess in China is widely distributed,continuous,with well-developed strata and large thickness.Most of Malan loess has loose structure,large pores and strong collapsibility and water sensitivity.The long-term infiltration process will cause the collapse of the framework structure of the loess,resulting in uneven settlement of the foundation and causing geological disasters.With the development of northwest China,loess has been widely used as the foundation of engineering construction,which puts forward higher requirements for loess engineering properties.As one of the important engineering properties of loess,permeability is closely related to the deformation and strength of loess,and has an important influence on the actual engineering construction.Therefore,it is of great significance to study the permeability improvement of loess.This article selects the shaanxi jingyang area of Malan loess as the research object,in the constant temperature box through a series of penetrant test reveal adding modifier under different ratio of blended influence on permeability of loess,at the same time through water chemical composition,mineral composition and microstructure changes of probing into the cause of the modified loess permeability coefficient variation law.The results show that:（1）Reconstituted loess soil is relatively loose,and easy to collapse.loess improved effects:lime>fly ash,when the mixture ratio of lime and fly ash is 15%,the ratio of lime-ash soil is 10:30:60,the improvement effect of loess is the best,The saturated permeability coefficient of the improved loess mostly decreases with time,especially when the ratio of lime to fly ash is 18%,it increases.（2）The exudate of soil and fly ash modified soil is weakly alkaline,At the initial stage of infiltration,the hydrochemical type of soil and fly ash exudate is slightly different,and in the later stage of infiltration,it is mostly HCO₃-Ca·Mg type.The exudate of lime and lime-ash soil ameliorated soil is strongly alkaline.Lime plays a leading role in lime-ash,and the hydrochemical type of soil is always CO₃-Ca type in the process of infiltration.（3）Before and after infiltration,the mineral composition of remolded and improved loess is mainly quartz,while the contents of plagioclase,calcite,illite and chlorite decrease in turn,and the contents of potash feldspar,dolomite and amphibole are less,mostly located below5%..Carbonation,sulphation and crystallization of calcium hydroxide have great influence on soil permeability,especially the calcite produced by carbonation reaction.（4）The skeleton grains of remolded loess are dominated by coarse particles with angular and semi-angular shapes and a small amount of fine particles.The contact modes between particles are mainly scaffold contact and Mosaic contact.The connectivity between pores is strong,and the degree of cementation is low.Improved soil skeleton particles type is given priority to with angular and half cone grinding,ash ratio increases,the coarse particle decrease,increase of degree of consolidation,the pore types mainly changed from elevated pores and intergranular pores to intergranular pores and cemented pores.The aggregates and agglomerates of lime and lime-lime improved soil increased significantly,and the particles were more and more closely arranged,and the pores became smaller and smaller,and the connectivity became worse.（5）The remolded loess belongs to loose soil,the contribution rate of large pores is the largest,and its structure is unstable and easy to collapse.The improved soil is mostly medium dense soil,and the contribution rate of Mesopores in the soil improved by lime and fly ash is the highest,followed by Small pores,and the contribution rate of Small pores gradually increases with the increase of the ash ratio.The variation trend of PAR of lime improved soil with the increase of ash ratio is consistent with the permeability coefficient,showing a"W"type.PAR of fly ash improved soil decreases with the increase of ash ratio.Compared with lime,the improvement effect is poor because of the large proportion of Macropores.When the lime content is constant,the content of fly ash increases,the Macropores disappear,the proportion of Mesopores decreases,the proportion of Small pores increases,and the soil compactness increases.