Study On The Dispersive Soil Modified By Silica-calcium Compound Systems

Dispersive soil is a type of water-sensitive special soil that is susceptible to erosion,scouring,and pipe surges under the influence of flowing water or other forms of damage,posing a serious threat to the safety of water conservancy projects.In engineering practice,lime,fly ash,and cement are commonly used to treat and eliminate the dispersivity of modified dispersive soil.However,the use of these traditional materials can lead to environmental pollution during the application process.Therefore,people are increasingly seeking environmentally friendly modified materials or ways to reduce the pollution caused by conventional materials.This paper proposes two silica-calcium compound systems for modifying dispersive soil based on the reaction principle between nano-silica and calcium chloride or calcium oxide.To investigate the dispersivity and disintegration of modified dispersive soil using two silica-calcium compound systems,this study conducted various tests including dispersibility,disintegration,physical,chemical,and microscopic analyses,and reveal the modification mechanism.The results provide scientific and technological support for the utilization of silica-calcium compound systems in modifying dispersive soil.The main conclusions of this study indicate that:(1)For the single silica system,both nano silica sol and solid nano silica can effectively inhibit the dispersivity of soil,and the effective dosing of each is 25% and 4%,with the dispersivity gradually decreasing as the content of nano silica increases.For the single calcium system,both calcium chloride and calcium oxide are capable of inhibiting soil dispersivity,and the effective dosing of each is 0.4% and 0.8%,with the level of dispersivity decreasing as the dosage of calcium chloride and calcium oxide increases.However,larger dosages of modified materials are required under the single silicon system.(2)The modification of dispersive soil using the nano silica sol-calcium chloride compound system enables the significant reduction of the dosages of both nano silica sol and calcium chloride while effectively eliminating dispersivity.The disintegration characteristics of the modified soil differed significantly from those of the dispersed soil,mainly in the shortening of the final disintegration time,the smoother disintegration curve and the absence of abrupt change points,and the insignificant change of the disintegration rate with the dosage of nano-silica sol and calcium chloride.It is recommended that the dosage of nano silica sol in practical engineering should be at least 1% and the dosage of calcium chloride should be at least 0.05%.(3)The solid-state nano-silica-calcium oxide compound system can effectively modify dispersive soil,with the influencing factors including the calcium-silica ratio,solid dosage,and reaction time.When the calcium-silica ratio is low,the dispersivity of soil gradually decreases over time.As the calcium-silica ratio and solid dosage increase,the required time to eliminate dispersivity is shortened.The disintegration resistance of the modified dispersive soil is improved in certain degree,and the disintegration resistance decreases with the increase of calcium-silica ratio.Considering the dispersivity and disintegration of the modified dispersive soil,it is suggested that the calcium-silica ratio is 0.5 and the solid dose is 2% in the actual engineering.(4)The modification mechanisms of the two compound systems are slightly different due to the differences in reaction principles between the various reactants.The modification mechanisms of nano-silica sol-calcium chloride compound system mainly includes: acid-base reaction reduces the alkalinity of the soil,ion exchange reduces the exchangeable sodium ion content,the physical filling effect of silica sol,the accelerating sol-gel effect of calcium chloride and the generation of cemented hydrated calcium silicate.The modification mechanisms of the solid nano silica-calcium oxide compound system mainly includes: the generation of cemented hydrated calcium silicate,acid-base reaction reduces the alkalinity of the soil,ion exchange reduces the exchangeable sodium ion content,the filling effect of solid particles and the agglomeration of soil particles.