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.