Effect of Angle and Lithology on Infiltrating to Fine/Coarse Dual-Structure Slope under Rainfall Condition

The occurrence of landslide is mainly caused by rainfall. Traditional treatment methods, such as spraying concrete on the surface of landslide to inhibit the penetration of rainfall on soil slopes, will fail during long-term operation resulted from failures, leading to landslides. Therefore, considering the ecological function and the long-term effectiveness of the reclamation method, this paper adopts the dual-structure of unsaturated capillary barrier layer (CBL) with fine/coarse lithology to prevent rainfall from infiltrating into the soil slope. The effects of slope (10°, 20°, 30°, 40°) and lithological characteristics (sandy loam/coarse sand, sandy loam/gravel sand, sandy loam/pebble and sandy loam/breccia) on the infiltration of rainfall into the soil slope were investigated through a series of physical model tests. Furthermore, a new method is defined to evaluate the total capacity of the capillary barrier (CCB) of the fine/coarse bilayer. The research results show that: (1) The process of preventing rainfall from infiltrating the soil slope with brilliant blue FCF (C.I.42090) dye tracer can be observed visually. (2) CCBS increases with the increase of coarse particle diameter, which is also related to the shape of pores and coarse particles, that is, the drainage efficiency of breccia with the same particle composition is higher than that of boulders. (3) The larger the slope angle of the four types of CBLS soil, the higher the drainage speed of CBL after rainfall, and the stable drainage strength and the total barrier capacity of loam/gravel sand CBL with rainfall intensity of 4.73×10^-4 cm/s, could increase firstly and then decrease with the increased slope angles. It is suggested that the design slope of CBLS is 25°-27°, in order to achieve the optimal total barrier capacity. The results of this study have a certain reference value for future landslide control.