Effect of adding natural clay on the water retention curve of sand-bentonite mixtures

Abstract

Sand bentonite mixtures are used in liners for many geo-environmental and waste containment applications. The gain in achieving appropriate hydraulic conductivity is commonly accompanied by unwanted swelling and cracking properties related to bentonite. Replacing part of the bentonite by natural clay of lower activity was found appropriate and improves the compressibility and cracking. This study is aimed at investigating the effect of partial replacement of bentonite with natural clay on the water retention capacity of sand-bentonite mixtures. The Soil Water Characteristic Curves (SWCC) for mixtures consisting of pure sand, 15% natural Qatif clay, 15% clay mixture (66.7% Qatif: 33.3% bentonite), 15% clay mixture (33.6% Qatif: 66.7% bentonite) and 15% bentonite were constructed using pressure plate tests. Fitting curves were performed using Fredlund and Xing equation. The general trends were examined and the effects of adding natural clay on the main features of the curves are listed. The SWCC can be used as a useful tool in predicting the flow through unsaturated sand-bentonite mixtures. The water retention capacity and SWCC profile of the sand bentonite mixtures are altered. The results provide a guide to predict changes in SWCC by adding different amount of natural Qatif clay.