Engineered barriers are used in the containment of hazardous materials and are usually a composite of compacted clayey soil and a synthetic membrane. Containment elements such as landfill liners should be designed to control or prevent leachate migration or groundwater ingress. Engineering specifications for a compacted clay liner are based mainly in a hydraulic conductivity less than 10-9 m/s and the need for stability during construction and operation of the landfill. Sandbentonite mixtures are often used as a barrier material. The addition of relatively small amounts of bentonite (5-15%) can improve the performance of a granular material providing both a low permeability and an enhanced mechanical stability. However not all the possible compaction conditions produce a low permeability and mechanically stable material. Changes in water content after compaction can cause swelling or collapse depending on the stress and suction conditions before the water content change occurs. A laboratory investigation of the swelling-collapse behaviour of compacted mixtures of Sand-bentonite has been undertaken. Compaction and suction characteristics were established. The suction and volume change characteristics were investigated through a series of oedometer tests. The central part of the experimental programme focused on the detailed investigation of the processes of swelling and collapse during controlled wetting.To do this, a significant number of modifications were required to the existing apparatus. Fabric studies including Environmental Scanning Electron Microscopy and Mercury Intrusion Porosimetry were also undertaken. Intrinsic behaviour and the relationship between suction and water content were comprehensively studied. A parametric study of the influence of bentonite content and sand grading was also undertaken. The results are presented and analysed. Recommendations for future research are made.