Abstract: The influence of cyclic drying and wetting on shear parameters (cohesion and internal friction angle) must be identified in calculating the earth pressure of filling by Xigeda soil involved with water. The shear stress-displacement curve of Xigeda soil was acquired from consolidated drained shear test under cyclic drying and wetting. Soil specimens were humidified by vacuum saturation and dehumidified in natural status to simulate the drying-wetting progress. The variations of peak shear stress, cohesion and internal friction angle with the number of drying-wetting cycles were analyzed. Furthermore, the relationship between macroscopic and microcosmic parameters was discussed by the parallel contact model, and the differences between bond and friction characteristics among micro particles were revealed. Test results showed that the wetting action reduced the cohesion and internal friction angle of the soil. As the number of drying-wetting cycles increased, the stress-displacement curves displayed strain hardening features to strain softening features, and peak strength, cohesion and internal friction angle all decreased and tended to be stable. In the first three cycles, cohesion decreased by 55.42%, while from the second to the forth cycle, internal friction angle decreased by 11.04%. The effect of drying-wetting cycle on cohesion was apparently greater than that on internal friction, and the deterioration effect on internal friction angle delayed. We recommend to weaken the influence of drying-wetting cycles on the mechanical properties of Xigeda soil by means from the aspect of the bonding effect among micro particles.

Key words: Xigeda soil, dry-wet cycle, shear properties, shear parameter, peak strength