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Desiccation crack formation is a key process that needs to be understood in assessment of landfill cap performance under anticipated future climate change scenarios. The objectives of this study were to examine: (a) desiccation cracks and impacts that roots may have on their formation and resealing, and (b) their impacts on hydraulic conductivity under anticipated climate change precipitation scenarios.Visual observations, image analysis of thin sections and hydraulic conductivity tests were carried out on cores collected from two large-scale laboratory trial landfill cap models (,80 3 80 3 90 cm) during a year of four simulated seasonal precipitation events. Extensive root growth in the topsoil increased percolation of water into the subsurface, and after droughts, roots grew deep into lowpermeability layers through major cracks which impeded their resealing. At the end of 1 year, larger cracks had lost resealing ability and one single, large, vertical crack made the climate change precipitation model cap inefficient. Even though the normal precipitation model had developed desiccation cracks, its integrity was preserved better than the climate change precipitation model.

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Abstract. The water retention behaviour of partially saturated MX-80 bentonite with pure water is relatively well investigated. However, in practical cases, the water contains a number of chemical compounds which affects the bentonite behaviour. In particular, bentonite is used in buffer applications of geological repositories for spent nuclear fuel, where the concentration of total dissolved solids in groundwater is expected to increase significantly with time. This paper investigates water retention behaviour of MX-80 type bentonite partially saturated with deionised water as well as 1M NaCl solution. In the experiments the specific volume of bentonite has been kept approximately constant.