| The disposal of nuclear waste has been becoming an urgent worldwide problem. Based on a comprehensive comparison of disposal techniques, deep geological disposal method has been widely accepted in the world. As the first choice to be used as engineering-barrier materials that can separate the nuclear waste from environment, characteristics of expansive clays attract more and more attentions of geotechnical engineers.Based on some lab tests and theoretical analysis on soil water characteristics, micro-structural characteristics and volume change behavior of Gaomiaozi bentonite, some results have been obtained. Gaomiaozi bentonite has high Na~+-monmorillonite content and liquid limit, great cation exchange capability and specific surface area, which is character by low permeability, high dilatability and good heat conductivity. For high suction, water content does not change so clearly with suction, so there is no significant difference of soil-water properties between unconfined and confined conditions. For lower suction, water content under unconfined conditions will change sharply with decrease of suction while under confined conditions it changes smoothly. The dilatability of bentonite under unconfined conditions is mainly from the swell of inter-aggregate pores, which leads to the forming of aggregates. Under unconfined conditions, pores distribution in bentonite becomes uniform. Under unconfined conditions, volume change behavior can be explained by diffuse double layer theory with a dry density of 1.7g/cm~3, but the prediction error will increase when suction decreases.
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