Development of a predictive model for the hydraulic conductivity of clay liners

The hydraulic conductivity is the most significant property of compacted clay used for waste disposal pits, solid waste landfills and retention ponds. Geotechnical engineering has experienced difficulties with the reliable prediction of hydraulic conductivity in the field. This study establishes a model for the prediction of the hydraulic conductivity of clay liners (compacted clay) based on its water content and dry unit weight. One of the frequently used methods of controlling the hydraulic conductivity of compacted clay is based on the above mentioned parameters employing laboratory and graphical means. The established model simplifies the process of predicting the hydraulic conductivity of compacted clay or clay liners.; General linear and polynomial regression analyses were carried out on data obtained from hydraulic conductivity tests on thirteen compacted clay soils used for clay liners at landfills throughout the United States. Of the 195 cases, 149 were used for model development and 46 for validation. The cases had collated data for hydraulic conductivity (K), water content (W), dry unit weight (D) and initial saturation (SI). Several models were fitted using the general linear regression modeling method with K as the dependent variable and W, D, SI or their combinations as independent variables. The dependent variable K was transformed to ln K (natural logarithm of K) for the general linear regression modeling. After rigorous analyses, diagnostics, and validation, three of the models, SI, WD and DSI were chosen as good predictors for the hydraulic conductivity of clay liners. However, model WD is recommended as the best based on statistical characteristics, the theory of hydraulic conductivity and practicality.; Ranges of water content and dry unit weight have been established for model WD to avoid predictions being made outside the scope of the model. Within the established region, the model can be used to predict the hydraulic conductivity for all levels of compactive effort. Therefore, it can be used to predict the hydraulic conductivity of laboratory compacted clay or field compacted clay. As such the model can be used for predictions during the design or construction monitoring stages of clay liners. Predictions made with the model are within the 95 percent confidence interval.; The probabilistic nature of the model WD and the consistency with which the model predicts the hydraulic conductivity make it more superior than existing models. The difference between predicted and measured hydraulic conductivity is 0 or 1 order of magnitude for model WD, while the difference for existing models established by researchers like Benson and Trast, and Harrop-Williams varies from 2 to 4 in the order of magnitude.