Modes and ecological damage effects of internal erosion of the redbeds

Investigations in redbeds distribution areas have identified internal erosion as a primary trigger of redbeds-related catastrophes, which include geological hazards, engineering failures, and ecological damage. Particularly in subtropical monsoon climates, internal erosion in bare redbeds leads to extensive ecological damage. However, a unified classification of internal erosion modes in redbeds remains lacking, and the distribution laws of internal erosion and their intrinsic links with ecological damage effects are not well understood. To systematically study the modes, distribution laws, and ecological damage effects of internal erosion in redbeds, this study integrates datasets of redbeds geological and environmental factors in China (such as temperature, precipitation, geological lithology, and vegetation coverage) based on GIS-based spatial overlay statistical analysis. It also combines field investigation methods including unmanned aerial vehicle (UAV) aerial survey, in-situ recording of internal erosion features, field sampling, and laboratory analysis to conduct a nationwide survey and in-depth focused analysis of typical regions (taking Shaoguan City, Guangdong Province as an example). The results indicate that: (1) internal erosion modes of redbeds can be divided into three types: open type, semi-open type, and closed type; (2) the distribution laws of internal erosion in redbeds has been clarified based on 7 subgrade types of geotechnical body and 13 regional types of climate and environment; and (3) in the bare redbeds within subtropical monsoon climate zones, internal erosion demonstrates rapid response and multi-process coupling, with the Si/Al ratio decreasing by 4.8 % during a one-year observation period, while the associated ecological damage follows a three-stage interfacial feedback process. This study establishes a systematic conceptual framework for understanding internal erosion in redbeds and provides a theoretical basis for researching its mechanisms and critical states, as well as for developing prevention and control strategies.