Abstract: A series of laboratory tests was conducted for investigating the swelling deformation characteristics after one-dimensional consolidation under different vertical pressures and the nonlinear strength properties after dry-wet cycles for remolded expansive soil/rock specimens, which were derived from the field test section in Nanyang and Xinxiang, where the Middle Line of Water Transfer Project from South to North China passes. The test results indicate that: (1) With the increment of vertical pressure, the shear strength of expansive soil obviously has two stages characteristics, that is to say, there is great difference between the strength parameters under low stress state and those under high stress state. (2) Under the same vertical pressure, swelling ratio of expansive soil decreases linearly with increment of original water content; while increases linearly with increment of original dry density. Swelling ratio expressions which simultaneously reflect the influences of original water content and vertical pressure, and the influences of original dry density and vertical pressure as well are presented, respectively. Moreover, a stress-strain relationship for soaking after one-dimensional consolidation is also presented. On the base of analysis, some suggestions are provided for expansive soil slope: (1) There are often shallow slides for slope of expansive soil, so strength parameters under low stress state should be measured and applied to its slope stability analysis. (2) High compaction degree for the shallow area of slope and toe of slope is inappropriate.

Key words: expansive soil, slope stability, expansive deformation, strength, dry-wet cycle