Effects Of Infiltration Water Hydrogeochemistry On Permeability Of Remolded Malan Loess

Loess is the Quaternary period,to wind-carried yellow powder deposits.In China,it is mainly distributed in Gansu,Ningxia,Shaanxi,Shanxi,Henan,Xinjiang,and other arid and semi-arid monsoon climate zones.In recent years,with the continuous promotion of urbanization and the continuous development of industry and agriculture,China has carried out a large number of engineering construction activities in loess areas,which has produced a large amount of remodeled loess,which has greatly changed the regional hydrogeological conditions,including the original regional soil infiltration characteristics,as well as infiltration,runoff,and drainage conditions.The research was conducted on the changes in the permeability of remodeled loess,the changes in water and soil chemistry during infiltration,and the calculation of the permeability coefficient using hydrochemical methods.In this study,the permeability of remodeled loess under infiltration of different chemical solutions and the hydrochemical reactions occurring during infiltration were investigated by using percussion tests,one-dimensional vertical saturation infiltration experiments,and hydrochemical experiments with the help of hydrogeochemical simulation techniques.A new way to calculate the infiltration coefficient of loess soils by the hydrochemical indexes of infiltration and percolation solutions was explored.The following conclusions were mainly obtained:（1）Deionized water infiltration conditions,the saturation permeability coefficient of the specimen with the experiment continues to become smaller,Mg Cl₂ solution infiltration conditions,saturation permeability coefficient growing,Ca Cl₂ solution infiltration conditions,the saturation permeability coefficient of the specimen with time growth,but the growth trend is relatively slow.The decrease of deionized water permeability coefficient is mainly affected by the clogging of large pore mineral dissolution and loss of cohesive force of soil particles by soil water erosion.the relative permeability coefficients of Mg Cl₂ and Ca Cl₂ solution infiltration show an increasing trend with time mainly due to the large hydration number of Ca²⁺and Mg²⁺,which makes soil particles produce coagulation causing clay layer dispersion and swelling,increasing the pore space between soils,and making the permeability coefficient increase.The infiltration coefficient increases.（2）Under the three dry density conditions,the p H,conductivity（EC）,and redox potential（Eh）of different infiltrating solutions were similar in the infiltration process.Under different solution infiltration conditions,the ion concentration of the leachate was high in the early stage and decreased and stabilized in the later stage,i.e.,the migration capacity of salt leaching became weaker with time.Under the deionized infiltration conditions,the trends of Cl^-,Na⁺,K⁺,Ca²⁺,Mg²⁺,SO₄^2-and Eh are basically the same,and they are leached out in large quantities at the early stage of infiltration,and the detected concentration of leachate decreases rapidly into the stable period.Under the conditions of infiltration of Mg Cl₂ and Ca Cl₂ solutions,Na⁺,K⁺,Ca²⁺,Mg²⁺,SO₄^2-and Eh follow the same trend,and are leached out at the beginning of infiltration,and the detected concentration of the leachate decreases rapidly into the stable period.period.However,the large amount of Ca²⁺and Mg²⁺infiltration affects the reaction of other cations in the soil column,and the homoion effect and ion exchange reaction will also lead to a slow increase of Na⁺and K⁺ions in the late infiltration.（3）The mineral composition of the loess soil was analyzed,and it was clear that the minerals involved in the reaction during solution infiltration were rock salt,fluorite,dolomite,calcite,sodium feldspar,gypsum,potassium feldspar.The mineral saturation indices of rock salt and dolomite were less than 0 under the infiltration conditions of deionized water,which indicated that the infiltrated solution would continue to dissolve the minerals in the soil,and the reverse simulation results indicated that the dissolution of rock salt and dolomite and the cation exchange of Ca X₂ and Na X.Under the conditions of Ca Cl₂ solution infiltration,except for dolomite,the saturation indices of all minerals were larger than those of deionized water infiltration,and the ion exchange reactions of rock salt,dolomite,CO₂（g）dissolution,and Mg²⁺ion exchange mainly occurred.reactions.（4）Calculation of the permeability coefficients of deionized water,Mg Cl₂ solution,and Ca Cl₂ solution under infiltration conditions by means of the water chemistry method of calculating the permeability coefficients of each of them was found:the difference between the permeability coefficients of infiltration of deionized water and the permeability coefficients calculated by hydraulics was large in the early stage,which was due to the destruction and collapse of pores caused by leaching,and the sudden change of pores between soils in a short period of time under the erosion of the infiltrating solution,resulting in The difference between the two methods was only 11.75%at the end of the experiment;the difference between the infiltration coefficient of Mg Cl₂ solution and the infiltration coefficient calculated by water chemistry was larger;under the infiltration conditions of Ca Cl₂ solution,the infiltration coefficients calculated by the two methods were more consistent with each other and the change trend was 25.6%.Thus,the conditions for the use of permeability coefficient calculated by hydrochemical index in loess soil are obtained as follows:the content of the calculated ionic components occupies a part of the total amount of solution ions,and the permeability coefficient calculated by using hydrochemical methods under such conditions is more reasonable;when the formula of permeability coefficient is calculated by water chemistry,the reaction of each ionic-mineral component in the percolation system is stable,and there is no sudden entry of new components into the system by water chemical solution in the middle;Groundwater seepage process should ensure that the reaction minerals are more stable and uniform,and there are no unknown minerals in the calculation process to influence the soil-water system.