Abstract. Granite residual soil landslides are widely distributed in the southeast of Guangxi, China. They pose threats to local communities, economic development and ecological restoration. To understand the failure mode, the landslide can provide a scientific basis for early warning and prevention. In this study, we conducted artificial flume model tests to investigate the failure mode of granite residual soil landslide. The macroscopic phenomena of landslides were observed and summarized. The response and variations of soil moisture content and pore water pressure were analyzed. And the discrepancies in landslide initiation were explored. The results had three aspects: (1) the response of volume moisture content was not synchronized with that of pore water pressure. Their variations were influenced by initial dry density, slope angle and rainfall intensity. The fluctuation of pore water pressure depended on soil mechanical behavior and its diffusion. (2) The differences in the formation process of granite residual soil landslides included the initiation time and mode. The starting time of landslide was delayed with increasing initial dry density and slope angle but shortened with increasing rainfall intensity. The failure mode could be changed from a sudden type to a progressive type due to the increase in initial dry density. (3) There are five stages in the landslide mobilization as follows: rain infiltration and crack generation, soil slide at the slope toe, occurrence of surface runoff and soil erosion, formation of steep-free surface, and soil slide at the upper slope. This research can provide valuable reference for the prevention and early warning of granite residual soil landslide in southeastern Guangxi.

Abstract. Granite residual soil landslides are widely distributed in southeastern Guangxi province, China. They are posing a huge threat to local communities and hindering social and economic development. To understand the failure mode of the landslide can provide a scientific basis for early warning and prevention. In this study, it conducted artificial flume model tests to investigate the failure mode of granite residual soil landslide. The macroscopic phenomena of landslides in the flume were summarized. The changes of soil moisture content along with pore water pressure were analyzed. And the differences and commonness in the initiation patterns of landslides were discussed. The results had four aspects. (1) There were significant similarities in the phenomenon of slope failures. In the beginning of the artificial rain, slopes were infiltrated, following by the slope toe soil softened and slipped. Another similar pattern was that continuous rainfall could cause soil crusts and runoff on the slope surface. Short-term low-lying areas and interlocking ditches would appear due to surface runoff and rainwater erosion. (2) The increase of initial dry density enhanced the permeability resistance of rainwater to the residual soil, which led to a delay in the response time of water content and pore water pressure, and a decrease in pore water pressure. Moreover, the fluctuation characteristics of pore water pressure may be related to the type of soil shear deformation. (3) The starting time of a landslide was delayed as the initial dry density and slope angle increased, but it was shortened due to the increase in rainfall intensity. Meanwhile, the initiation pattern changed from a sudden sliding type to a progressive failure type due to the increase of initial dry density. (4) The failure process of the granite residual soil landslide could be classified into five stages: rainwater infiltration, soil sliding at the slope toe, the occurrence of surface runoff and erosion, the formation of a steep free face, and the upper soil sliding. Above research results can provide valuable references for the prevention and warning of granite residual soil landslide in southeast Guangxi.