Typhoon-induced slope failure is one of the most important geological hazards in coastal areas. However, the specific influence of typhoons on the stability of residual soil slopes still remains an open issue. In this study, the Feiyunjiang catchment in Zhejiang Province of SE China was chosen as the study area, and a downscaling physical model of residual soil slopes in the region was used to carry out the wind tunnel test. Our aim was to answer the question, How does the vegetation on the slope and slope stability respond during a typhoon event? For this purpose, multiple aspects were monitored and observed under four different wind speeds (8.3 m/s, 10.3 m/s, 13.3 m/s, and 17 m/s), including vegetation damage on the slope, macrocracks on the slope surface, wind pressure, wind load, permeability coefficient of the soil layer, and slope stability. The results showed that the plants on the slope could restore to their original states when the wind speeds ranged from 8.3 m/s to 13.3 m/s, but were damaged to the point of toppling when the wind speed increased to 17 m/s. Meanwhile, evident cracks were observed on the ground under this condition, which caused a sharp increase in the soil permeability coefficient, from 1.06 × 10⁻⁵ m/s to 6.06 × 10⁻⁴ m/s. The monitored wind pressures were larger at the canopy than that at the trunk for most of the trees, and generally larger at the crown of the slope compared with the toe of the slope. Regarding the wind load to the slope ground, the total value increased significantly, from 35.4 N under a wind speed of 8.3 m/s to 166.5 N under a wind speed of 17 m/s. However, the wind load presented different vector directions at different sections of the slope. The quantitative assessment of slope stability considering the wind load effect revealed that the safety factor decreased by 0.123 and 0.1 under the natural state and saturated state, respectively, from no wind to a 17 m/s strong wind. Overall, the present results explained the mechanism of slope failure during typhoon events, which provided theoretical reference for revealing the characteristics of residual soil slope stability under typhoon conditions.

Fractures are the dominant conditions for rainfall infiltration into slopes, which can aggravate the instability of landslides. However, few studies have been conducted to analyze in detail the instability and deformation characteristics of creeping landslides with fractures. In view of this, this study investigated a landslide in Fu’ao Village, Wencheng County, Zhejiang Province in China to determine how fractures affect landslide deformation and instability during heavy rainfall through an in situ simulation experiment. In the experiment, three consecutive days of rainfall were set up based on Typhoon Megi in 2016, and two conditions were simulated, namely, rainfall + water filling fractures and rainfall + filled fractures (also referred to as the first and second conditions, respectively). The changes in the volumetric water content (VWC), pore water pressure (PWP), and deep displacement of the landslide at a depth of less than 5 m under the two conditions were observed using field monitoring instruments. The simulation results were as follows: (1) The volumetric water content of the shallow soil showed a more sensitive time-varying response to rainfall, while that of the soil at a depth of more than 200 cm showed a lagged response to rainfall, with a lag of about 10 h, which decreased significantly in the case of the unfilled fractures; (2) Under the first condition, the pore water pressure at different depths showed almost the same changing amplitude of 5 kPa or less. Under the second condition, the pore water pressure increased significantly with depth during the rainfall, with the changing amplitude reaching 30 kPa; (3) The displacement of the borehole equipped with the inclinometers near the front of the slope was higher than that at the borehole equipped with the inclinometers near the rear of the slope. The displacement under the first condition was up to 6 mm, which was significantly greater than that under the second condition. Therefore, fractures have significant effects on the instability of landslides induced by typhoon-triggered rainstorms, and one important measure to prevent and control this type of landslides is to fill fractures in the landslides in time.