Experimental And Numerical Modeling Of Chemical Osmosis In The Clay Samples Of The Aquitard In The North China Plain

The problem of groundwater flow and solute transport in low permeable cohesive clay and sediment is one of the research topics of the groundwater field.Different with the traditional high permeable agent of groundwater problem,the low permeable agent exerts "semipermeable membrane"property which is similar to the biological membrane.The inner groundwater not only get the driving of hydraulic gradient but also receive the driving form component conjugate gradient of concentration gradient(chemical osmosis),voltage(electro-osmosis)and temperature difference(thermo-osmosis).The chemical osmosis is the most obvious problem among groundwater flow issues.In the recent years,this low permeable agent coupling flow problem which is drived by different gradients is applying to more and more various researches,however,the research of clay semipermeable membrane effect's chemical osmosis phenomena seldom have been involved.This thesis discusses the point of view from chemical osmosis phenomena on move-down mechanism of North China Plain typical brackish water termination.The assay firstly summarizes the research background,meaning and the chemical osmosis phenomena research of clay semipermeable membrane effect,which includes indoors experiment,field test and the field evidence of chemical osmosis phenomena.In allusion to the clay's "electrical double layer",we sum up with different assessments of?clay membranous discontinuity models.According to the contrast test,? increases with Cation Exchange Capacity(CEC);decreases by the increasing of porosity and solution concentration.For more intuitively comprehending the semipermeable membrane effect of clay,this thesis makes use of the rigid wall permeameter to measure the permeability and the reflection coefficient ?from the undisturbed clay of North China Plain typical saline water area and the remolded clay which is made by it.After the permeability test,which the concentration difference is 0.152M,we measure the undisturbed clay's ois 0.013 and the remolded clay's ?is 0.089.Although both of the clay samples have the same compound and porosity,the membranous of undisturbed clay is littler than the remolded clay's.This shows when the clay particles arrange in a more order way,the clay would exert higher membrane property.After the reverse osmosis(ultrafiltration)test,which the head difference is 10m and the concentration difference is 0.1092M,there is no ?measured cause the undisturbed clay breaks when the water head rose and the remolded clay's ois 0.28;when the head difference is 20m,the remolded clay's ?is 0.238.Acquiring bigger ?than the chemical reverse osmosis.In the meanwhile,the assay discusses what measured by different discontinuity models and compare with the test results,and indicate the Bresler Model seems be better matched up with the actual results.To fit the time-varying relation between the pressure difference and differential concentration in the experiment,we introduce a continuous model.And then modeling the indoors test results by this continuous model.The model fit the test results quite good when there are logical parameters.What s more,this continuous model also fit the Noy(2004)field test result really good.Analyzing the sensibility of every parameters in this model to making sure the different degrees of influence from various parameters to the evolutionary process of the pressure curve.And in the test,?mainly influences the number of pressure peak,the dispersity D mainly influences the rate of decay after the pressure curve reach the peak,and the clay's permeabilty kand the elastic storativity Ss of porous stone have great influence to the peak time of the pressure curve.Taocheng district Hengshui City where located at the brackish water typical area of North China Plain,we compare our brackish water surface move-down situation with previous research,and we find out the move-down speed is relatively slow.Considering there is a membrane properties of this area's clayey stratum and there may form a typical chemical infiltration system in the underground aquifer system of this area,and the chemical osmosis pressure offset the downward water head difference which caused by excessive collection of deep fresh water to some extent,and then decrease the moving down rate of the brackish water surface.In the meanwhile,modeling the evolution of osmosis pressure at the North China Plain typical brackish water section,and the east part of the section has higher up osmosis pressure because of higher concentration,while the third and fourth aquifer reach the pressure peak later than the second aquifer because of bigger thickness.On the circumstance of taking no account of human factors and other geological structure influence,the osmosis pressure peak number can reach near 60m in some areas.So there are ubiquitous chemical osmosis phenomena existing in the brackish water aquitards on the North China Plain.Obviously,when studying the move-down mechanism of brackish water surface of this area,we cannot ignore the influence that the chemical osmosis effect of brackish water clayey to the moving down of its surface.