Shear behavior of the interface between expansive soil and sand liner during wetting-drying cycles

抄録

A series of direct shear tests are carried out on the interfaces between expansive soil and sand liner during wetting-drying cycles. Several factors impacting the shear behavior are discussed, including wetting-drying cycles and saturation methods. Upto 5 times of the wetting-drying cycles are applied on expansive soil-sand liner samples before shearing. Saturation methods comparison is carried out under confined and unconfined conditions, which means whether the samples are fully restricted in a saturator or are able to swell freely during saturation. Test results show that the interface behaves strain-hardening and the shear zone extents to a certain depth in sand liner. The shear strength is higher under confined saturation condition than that under unconfined saturation condition,the friction angles under confined saturation condition are about 0.4 to 9.7 degrees greater than those under unconfined saturation condition at the same wetting-drying cycle. As wetting-drying cycling, the friction angle increases under confined saturation condition, while it increases at beginning and then decreases under unconfined saturation condition. The mechanism of the interface friction angles behavior is revealed as the combination result of two aspects: sand particles merge into expansive soil and samples compacted by expansive force, which increases the density of the “shear band” and sample, and fissures grow, which destroys the integrity