Abstract: A profound understanding of hydro-mechanical coupling process in rainfall-induced landslides and its formation mechanism are prerequisites for the accurate early warning. In this study, a typical landslide in Wenchuan earthquake region is selected for a series of full-scale artificial rainfall tests, to simulate failure progress on gravelly soil slope of landslide deposit. Two classical soil-water characteristic curve (SWCC) models, Brooks-Corey (BC) and Van Genuchten (VG) model, are used to establish the SWCC during rainfall infiltration. Then, the stress state and stability of slope are analyzed by one-dimensional variably saturated infinite slope model. The results reveal that the slope failure is the consequence of dual-permeability interaction between the preferential flow and the matrix flow. The VG model is capable of fitting SWCC of wide-graded gravelly soil during wetting process for preferential flow. Comparison between stability analysis and observation indicates that changes on volumetric water content, matric suction and surface inclination are consistent with calculated suction stress and safety factor. Finally, the seepage erosion in unsaturated slope is proved by the tests, and the migration of fine particles is statistically analyzed. Based on the physical model test, this study reveals the coupling process of soil-water characteristic curves and slope failure with the influence of preferential flow under rainfall conditions, which can provide reference and basis for the prediction and early warning of unsaturated slope instability.

Key words: unsaturated, gravelly soil, shallow landslide, full-scale model test, hydro-mechanical coupling