Abstract
A new method for calculation the membrane efficiency coefficient w of compacted clay is proposed in this paper. The influence of fixed negative charge on the surface of clay minerals is considered. What’s more, the change of porosity during deformation is considered. Based on the chemical potential of specimens, the true ion concentration in pore-water is obtained. Based on the true ion concentration in pore water, the disjoining pressure considering fixed negative charge inside soils and the change of void ratio is proposed. A new calculation method for the membrane efficiency coefficient of compacted clay is established. The test data of w considering different porosity are calculated and the calculated results are compared with the traditional calculation methods. The new calculation methods of w provide a more physical-based theory for environmental geotechnical engineering.
Highlights
Membrane efficiency coefficient is the behaviour of porous medium to restrict the migration of solutes
Due to the semi-permeable membrane behaviour, compacted clay has been used as the engineering barriers in environmental geotechnical engineering to inhabit the migration of solutes harmful to humanity [1]
Where cK+ and cCl- are the true concentration of K+ and Cl- in pore-water, n is the porosity of the compacted clay, c is the measured pore-salt concentration, cfix is fixed charge density, which can be calculated by the following equation c fix 10 CEC d
Summary
Membrane efficiency coefficient is the behaviour of porous medium to restrict the migration of solutes. The membrane efficiency coefficient of compacted clay can be affected by many factors (such as the porosity, the concentrations of ions in pore-water, the mineral composition). Experimental results have shown that the membrane behaviour of compacted clay would be enhanced with the decrease of the porosity [6,7], the increase of the bentonite content [8], and the decrease of pore-fluid concentration [9,10,11]. Until now, the van’t Hoff equation has been used to calculate the theoretical pressure difference of the tested specimen by most researchers [14]. What’s more, the true ion-concentration in pore-water and the effect of deformation are not considered by the above theoretical chemico-osmotic pressure difference. The true ionconcentration in pore-fluid and the effect of deformation are considered in the new theoretical chemico-osmotic pressure difference and membrane efficiency coefficient
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