Experimental Study On Engineering Property And Modification Mechanism Of Dispersive Soil Modified By Fly Ash

Dispersive clay is one of the problematic soil concerned in geotechnical engineering recently.Dispersive clay has low erosion resistance ability and the process of destruction is rapid and secluded,so it does great harm to water projects in dispersive clay area.As a coal-fired power plant secondary product,the fly ash has a certain activity and cohesion.So the fly ash can be used as modifier for dispersive clay because of its low compressibility,high strength,and well water stability.Based on mechanism of dispersity of cohesive soil,the pinhole,crumb,compression,unconfined compressive strength,seepage deformation,SEM and MIP tests had been investigated in different fly ash contents,curing period and compaction degree,so as to study the effect of fly ash on the dispersity,deformation property,strength property,impermeability and microstructure characteristics.The modification mechanism of fly ash also had been analysed in this reasearch.The conclusions of this study are as follows.(1)The fly ash had a great modification effect on the dispersibility of dispersive soil.The influencing factors mainly included the fly ash contents,curing period and compaction degree.With the increase of the contents of fly ash,the extension of the curing period and the improvement of the compaction degree,the dispersibility of the dispersive soil was disappeared gradully,which the first was the transitional soil,and then was the non-dispersive soil.In the actual project,the fly ash should be more than 4%,the curing period more than 7 days,and the compaction degree above 96%.(2)The fly ash could effectively reduce the compression deformation,improve the strength and impermeability of dispersive soil.With the increase of fly ash contents and curing period,the compressibility of soil gradually decreased.After 7 days of curing period,the compressibility of the soil was basically in a stable state.At the early stage of curing period,the fly ash contents had no effect on the unconfined compressive strength of dispersive soil.The unconfined compressive strength increased with the increasing of the curing period and the fly ash contents.The impermeability of the soil was enhanced and the permeability stability of the soil could be improved when the fly ash were added into the dispersive soil.(3)The main mechanisms of dispersive soil modified by fly ash included hydrolysis and hydration reaction,ion exchange reaction,hardening reaction,etc.Accompanied by these reactions,the compressibility of soil was obviously reduced,the unconfined compressive strength and impermeability were significantly improved.The SEM tests showed that the quantity of hydration products change significantly with the increasing of fly ash contents and curing period,leading to an increase in contact area between framework grains,a reduction in intergranular pore and a transformation from point-contact to surface-contact.The MIP tests demonstrated that the quantity of soil pores with diameter of 1 to 10 ?m decrease,but the quantity of soil pores with diameter of 0.1 to 1 ?m increased with the increasing of fly ash contents and curing period.