Data set construction
Topographic and geomorphic factors
Elevation, slope, planar curvature, profile curvature, surface roughness, surface roughness, coefficient of variation, and landform type data can reflect the complex and diverse terrain conditions and directly or indirectly impact the stability of slopes (W.A. Zhang et al. 2023; X.M. Li, Cao, et al. 2023). In karst regions, planar curvature and profile curvature influence the erosion rate of karst areas(X.W. Yang 2019). Terrain roughness, surface roughness, and coefficient of variation affect surface runoff velocity, the transport and deposition of slope materials, and consequently influence soil infiltration and runoff generation time(Amen et al. 2023; Bi et al. 2023).
Normalized Difference Vegetation Index (NDVI) reflects the surface vegetation cover, and in general, areas with higher vegetation coverage have better soil and water conservation, which enhances the stability of geological formations. However, in karst regions, the relationship between vegetation types and soil-climate factors can affect the erosional effects in the karst areas (Shuai et al. 2023). In the study area, the soil is mainly acidic red soil, and the respiration of plant roots generates a large amount of CO2, which leads to the fragmentation of the surface rock layers and increases erosion. Additionally, the decay of the litter layer and subsequent microbial activities also produce organic acids and a significant amount of CO2, providing favorable conditions for continuous karst processes but unfavorable for the integrity of rock structures.
Basic geological factor
The distance of faults reflects the influence of tectonic activity on the development of rock joints and fractures (Y.Y. Li, Chen, and Shang 2017). Rock lithology is an important indicator reflecting the physical properties of rock and soil, including shear strength, among others (Samodra et al. 2016). The study area is predominantly composed of high-purity carbonate rock, accounting for over 90% of the total area of the study region.
Meteorological and hydrological factors
Rainfall affects the deep infiltration of rock and soil, thereby altering the strength of the rock and soil and subsequently impacting the stability of slopes. In karst regions, rainfall is a crucial water supply source for the karst process, and studies have shown a positive correlation between rainfall and karst erosion(Qian, Wu, and Li 2013; Wu et al. 2020; Zhou et al. 2023). Under favorable rain and heat conditions, the rock is more susceptible to dissolution by water, resulting in the formation of dissolution voids that reduce the integrity of the rock and promote rockfall. The distance to water systems reflects the spatial distribution of water systems in the karst region and indirectly indicates the extent of water system erosion in the study area.
Human activity factor
The construction of roads, especially the slope excavation during the road construction process, alters the slope's original condition, changes the stress distribution of the slope, and increases the probability of disasters. The blasting activities during road construction and the dynamic loads generated by the movement of large vehicles after road completion have adverse effects on the surrounding unstable geological formations.
Data set analysis
The majority of this study adopts the natural breakpoint classification method, which minimizes the differences within each category and maximizes the differences between categories, ensuring category consistency. Due to limitations in data sources, there are instances where certain factors have no disaster points within their interval ranges. To reduce the error caused by handling such data, a discretization approach is employed in the treatment of disaster points to avoid invalid information.
Through the analysis of information values, it is found that the development pattern of rockfalls in the study area is similar to the patterns discovered in most studies on rockfall susceptibility evaluation concerning factors such as slope, rainfall, fault distance, and road distance. However, there are differences in the consideration of certain factors:
(a) The primary lithology in the study area is carbonate rock, which is relatively hard. The rock mass exhibits varied karstification and weathering degrees, leading to different overall integrity of the rock mass. Therefore, considering the rock mass combination types rather than solely focusing on the shear strength and compressive strength of the rock mass is more crucial for karst areas. In this study, the rock mass combinations in the research area are categorized into moderately thick bedded hard to semi-hard strongly karstified carbonate rock groups, moderately thick bedded hard to weak to moderately karstified carbonate rock with interbedded clastic rock groups, and thin to thick bedded hard to weak clastic rock groups.
(b) In the study area, rockfalls occur within the NDVI range of 0.65 to 0.75. The development of rockfalls is unfavorable when NDVI is lower than 0.65 and higher than 0.83, indicating that vegetation conditions have varied effects on the development of rockfalls in the research area.
(c) Regarding landform types, peak clusters and depressions are favorable for the development of rockfalls in karst areas.
(d) Factors such as coefficient of variation, planar curvature, profile curvature, and surface roughness all have promoting effects on the development of rockfalls, suggesting that the role of water in the occurrence and development of rockfalls in the study area cannot be ignored.