Prediction of the hydraulic conductivity of clays using the electric double layer theory

A model to predict the hydraulic conductivity of consolidated clay, simulating clay liners compacted wet of optimum, is presented. The concept that clays exist as clusters and the electrical double layer theory are used to predict the hydraulic conductivity of clays for permeants of known composition. The model relates the physical properties of clays, such as its surface area, with the overburden pressure and the concentration of ions in the permeant. The model can be used to predict the hydraulic conductivity of bentonitic clays with monovalent as well as divalent exchangeable cations. The model is valid within the range of applicability of the Gouy-Chapman electric double layer theory. The variation in the number of clay particles per cluster with the consolidation pressure and concentration of ions in the permeant has been discussed. The model has been calibrated and verified using published experimental data. However, the model in its present form is valid only for homoionic clays and permeants with the same valency. With an increase in concentration of ions in the permeant, the precision of the model has been found to decrease. Key words: clay, clusters, hydraulic conductivity, double layer, model, permeant, concentration.