Abstract: The specimens of Nanyang expansive soil compacted at the same initial condition, were subjected to one to six wetting-drying cycles; and then the specimens after one, three and six wetting-drying cycles were selected for measuring the relationship between suction, water content, void ratio and saturation degree by the vapor equilibrium method using saturated salt solutions; and thus the soil-water characteristics of compacted Nanyang expansive soil was analyzed. When every drying process finished; the picture of the specimen top surface was taken. The pictures were dealt by the digital image processing using cutting ring as a frame of reference, and then the shrinkage and crack areas were extracted. The shrinkage and crack areas developing with drying-wetting circles were analyzed by calculating the ratios of shrinkage and crack areas to cutting ring area. The test results show that with the increasing of wetting-drying cycle, water content decreases, void ratio increases and water retention capacity decreases, and the shrinkage and crack areas after oven dry increase. But the changes in the above behavior become less with increasing the cycle. The above test results are useful to study soil-water and shrinkage characteristics of expansive soils during drying-wetting circles.

Key words: expansive soil, soil-water characteristics, vapor equilibrium method, wetting-drying cycle, image processing