A Laboratory Study on the Geotechnical Characteristics of Sand–Bentonite Mixtures and the Role of Particle Size of Sand

Mixtures of sand and bentonite are generally used as a liner material at the waste disposal site. Sand is added to bentonite to achieve a higher compaction density and lower desiccation shrinkage. A review of the literature showed that most of the past research works has focused to study the influence of bentonite on the various geotechnical properties of sand–bentonite mixtures. Although sand occupies a larger proportion in a sand–bentonite mixture, the effect of proportion of sand and its particle size on the characteristics of the sand–bentonite mixture is still unclear as very little information is available. This study is an attempt to understand the effect of the particles size of the sand on the behaviour of various sand–bentonite mixtures mixed in different proportions. Various mixtures of fine sand–bentonite and medium sand (MS)–bentonite were prepared by varying the sand content from 50 to 90 % by dry weight of the mix. Mixtures were tested for Atterberg limits, compaction characteristics, swelling and hydraulic behaviour. Results indicated that variation in liquid limit is not linear even though the clay content in the mixes varied linearly; mixtures with fine sand (FS) displayed relatively higher liquid limits compared to MS counterparts. FS mixtures exhibit relatively high optimum moisture content and low maximum dry density. Consolidation test indicated that irrespective of the sand particle size, mixes with bentonite content <20 % showed a general lack of appreciable swelling. This implied that bentonite content available was not sufficient for filling the voids created by sand skeleton. For the same bentonite content, mixtures with FS displayed relatively higher swelling pressure and lower hydraulic conductivity. For a given void ratio, FS mixtures exhibited lowest hydraulic conductivity for all bentonite contents.