Experimental Study On Dispersion During Saline Water Flow Through Clay-bearing Soil

The North China Plain is the political, economic, cultural and transportation center of China, and there are severe contradictions between supply and demand of water resources. The main water resources of the North China Plain is groundwater. The thickness of Quaternary system of this area is 450-600 m, containing 4 water-bearing layers:the first one is called shallow(superficial) saline water, and the other three layers are deep fresh water. The fact that saline water is in the superficial and fresh water is deep makes the water quality structure of this area. The deep water no longer discharged to superficial water and turned to accept the recharge from shallow water because of the long-time over pumping. The salinity of deep water did not arised although there entrained a lot of shallow saline water. The equilibrium analysis of salt shows that the shallow saline water turned fresher because of the leakage flow. The aim of this paper is to study on dispersion during saline water flow through clay-bearing soil, which is an important application of the exploitation and protection of deep water resources. Study on dispersion effect by indoor experiment and calculation and lay the foundation to study the mechanism of "the desalting of saline water".There are several theories about the desalination of soil:Bredehoeft hole the opinion that the soil partical refrained the passage of anion and, at the same time, the cation can not pass since the attraction of anion. As a result of that, only water molecule whose ionization degree is small. Hanshaw, et al. explain the fact in the other way. When solution pass through soil layer with pressure, the side of soil pore will have electric potential. The side flowing out is positive electrode and the side flowing in is negative electrode. Cation can not move to the side flowing out since the exclusion of electron charge. At the same time, there are theories of electric double layer in the surface of soil particles, et al.This paper study the mechanics, process and influencing factor of the reaction between saline water and soil during the leakage of saline water by indoor experiment. The theory of experimental model is similar to Darcy seepage experiment's. The soil samples and core(原状土)are from Shijiazhuang and Caofeidian in Hebei province and Yizhuang in Beijing. The samples for column experiment is oven-dried, pulverised and sieved which is promised to smaller than 0.1 mm. At the same time, osmotic experiment of soil core from Caofeidian is proceeded by TST-55 osmoscope. Concentration breakthrough curve is drawed and dispersion parameter is calculated.Analyze the data from different soil samples and experiment equipment could get the conclusion that the soil samples whose hydraulic conductivity is smaller and the flow velocity in it is slower have smaller dispersivity. Under the same experimental condition, the soil samples whose dispersivity is smaller could retain more salt ions from the solution flow through the soil.The fact that soil samples in these experiments could retain salt ions also explains the phenomenon before that although in the big scale of the North China plain there is leakage flow from the shallow saline water to deep fresh water, the salinity of deep water did not arised.