Abstract: The hydro-mechanical behaviours of bentonite are prone to be affected by the wetting-drying cycle due to its swelling-shrinking deformation characteristics with the moisture changing. Vapor equilibrium method using saturated salt solution, is used to measure water-retention behaviour of compacted Gaomiaozi Calcium bentonite after wetting-drying cycles. The specimens compacted at the same initial condition, are subjected to one to six wetting-drying cycles, and then the original specimen and the specimens after three and six wetting-drying cycles are selected for measuring their water-retention curves(WRC). When every wetting-drying cycle finished, the pictures of the specimen surface are taken. The pictures are dealt by the digital image processing, and then the shrinkage and crack areas are extracted. The rates of shrinkage and crack to original specimen area are obtained. Test results show that, with increasing wetting-drying cycles (0→3), the WRC moves down, water retention capacity and average skeleton stress decrease. Void ratio, the rates of shrinkage and crack after oven dry increase obviously. But after three cycles (3→6), the changes in the above mentioned behaviour become stable with increasing wetting-drying circle.

Key words: bentonite, vapor equilibrium method, water-retention behaviour, wetting-drying cycle, image processing