| Saturated-unsaturated soil water infiltration is an important part in the circulation of nature water.In the process of infiltration,with the convection and diffusion of the soil moisture,pollutants in surface water can rapidly infiltrate into groundwater through weakly-protected strata,recharge zones,directly-exposed groundwater skylights,and other zones that have direct hydraulic connections with groundwater,and can also consistently accumulate diffuse down through strongly-protected strata to cause groundwater pollution.Consequently,river channels or ditches that convey polluted surface water inevitably become the main sources of groundwater contamination.The "Cenozoic aquifer",caused by the infiltration of surface water and the recent large-scale leakage is usually the most contaminated groundwater.About nearly70% of China's population is using groundwater.The polluted groundwater will have severe influence on human health and even social stability.Therefore,it becomes an important project to prevent surface pollutants from migrating into deeper layers of soil or groundwater through soil-water convection,and to control ground water pollution from surface pollutants.Based on Shanxi River Management and Protection Services Program under Sci.2012-1,Jincheng City Science and Technology Development Project under No.201202238 and Shanxi Province Science and Technology Development Project under No.20150313002-2,the paper took the riverbed sediment matrix from the mainstream and branches of Fenhe River in Shanxi Province as experiment matrix,and analyzed the process of water infiltratinginto riverbed sediment matrix,the pollutants migration process,and the interception effects of pollutants in wastewater when cement infiltrating into riverbed sediment matrix.In the research,we first compared the permeability-reducing effects of different fine particulate matters such as fly ash,clay,cement,blast furnace slag,when they infiltrating into sediment matrix respectively,and then choose cement as fine permeability-reducing material due to its better permeability-reducing effect and operability.Furthermore,we analyzed the interception effects of various nutrient elements and pollutants in wastewater when cement infiltrating into the sediment matrix.The results show that:The fine particulate matter can obviously reduce the moisture infiltration capacity when it is smaller than the principal component particles of sediment matrix,and can effectively infiltrate into the riverbed sediment matrix;And the permeability-reducing effect depends on the comprehensive performance of sediment matrix and fine particles;By comparing the permeability-reducing effect of selected fine particulate matters,the results show that the cement has the best permeability-reducing effect,and the effect of clay,fly ash,blast furnace slag decreasing in turn.Cement is one of ideal permeability-reducing matter because of its economy and practicability.Clay,fly ash and blast furnace slag are not suitable due to smaller proportion,poor gelling property and so on.There are many factors influencing the permeability-reducing effect of cement infiltrating into the riverbed sediment matrix,but the initial waterhead of cement infiltration,the postponing time of water supply,dry density of the sediment matrix,sediment matrix texture and cement addition quantity etc.are the main factors.Through the simulation analysis with SPSS,we found that the selected dominant factors can be used as the independent variables to determine the multivariate linear model and multivariate nonlinear models and to predict thepermeability-reducing effect of cement infiltrating into the riverbed sediment matrix.The average prediction errors are 5.86% and 6.16%.The multiple linear prediction model,with simple form but relatively high precision,can be used in the earlier study.Sediment substrates had certain interception effect on the pollutants in the infiltration wastewater mainly migrating down by convection;Cement infiltrating in sediment can improve the interception effect of sediment substrates;Based on the analysis of the seepage water at 1 m of embedded depth,the interception effect on SS can be increased by about 70% on the condition of cement infiltrating into sandy sediment substrates;The interception effect on NO3--N,NH4—N and heavy metals can be improved by over 40%;The interception effect on TP,SO42-and Cl-can be enhanced by about 20%.As for the TDS content in sewage,cement infiltrating in sediment did not show obvious interception effect.There are strong effects on the longitudinal distribution trend of the pollutants in the sediment matrix under the condition of cement infiltrating into sediment matrix,but insignificant influence on the longitudinal distribution trend of and TP etc;The longitudinal distribution trend of SO42 – salt and heavy metal elements shows the phenomenon called " Shallow accumulation & surface gathering”,and the impact is obvious;In different depth of soils,the contents of various pollutants in treated samples are less than that in the reference samples to a certain extent.Cement infiltrating in sediment matrix has certain inhibition effect on the total amount of exogenous pollutants into soils.Detailed mechanism analyses are made based on the study results.The results show that selected Portland cement,with 91% of the particles in the 3-32?m diameter range and the proportion being up to 3.1,can easily infiltrate into the soil matrix.Before or in the process of polluted water infiltration,cement infiltrating in the river sediment matrix can fill the pores between the soilparticles,and then reduce the porosity and increase the resistance of the water flow in the pores.With good hydraulic coagulability and adsorption to soil moisture,cement infiltration can form the compact permeability barrier of poor permeability and high hardness,which has obvious interception effect on pollutants in the infiltration sewage such as nutrient elements,salt and heavy metals etc.and its interception effect is above 35%;Therefore,it is an effective measure to control groundwater pollution.The study provides guidance for using modified soil to influence soil permeability characteristics and reducing and controlling the groundwater pollution caused by the river and canal sewage pollution.Because of the restrictions of test condition and experiment cycle,only the physical factors influencing cement infiltrating into the sediment substrates were studied in this paper.The study of other factors and the interaction,mathematical relationship and prediction models still need to be carried in the future. |
PDF Full Text Request