Preliminary analysis on basic characteristics and mechanism of rockfalls in layered red rocks with gentle dip angle: A case study of the Tiejiangwan rockfall in Hongya County, Sichuan Province

Gentle dip angle rock slopes are often developed in layered red rocks, which are prone to geological disasters due to the combination of soft and hard lithology. This paper discusses the Tiejiangwan rockfall that occurred on April 5, 2021, in Hongya County of Sichuan province, China, on a layered red rocks slope with a gentle dip angle. Using an air-space-ground integrated earth observation network, including optical remote sensing, UAV aerial photogrammetry, and on-site investigation, the study analyzes the basic characteristics and mechanism of rockfall and predicts the development trend of similar disasters in the steep cliff area of layered red rocks. The results show that the Tiejiangwan rockfall can be divided into two areas, namely the main rockfall area and the rockfall influence area. The main rockfall area comprises one rockfall source area, one shoveling area, one accumulation area, and one water secondary transportation accumulation area. The rockfall influence area includes one potential rockfall source area and five disturbance deformation areas. The rockfall source area has a combination of hard rocks at the top and soft rocks at the bottom, and the rock mass develops two groups of nearly vertical dominant structural planes. In 2013, the source area showed signs of deformation, which eventually lead to the instability of the dangerous rock mass due to the continuous effect of rainfall and temperature differences. The huge impact force caused the rockfall debris flow disaster chain, affecting the old rockfall accumulation body and bedrock under the dangerous rock mass. Optical remote sensing images and field investigation indicate the risk of secondary collapse in Tiejiangwan rockfall. Additionally, six similar potential rockfalls were identified in the adjacent area. To prevent similar disasters, it is recommended to use UAV aerial photogrammetry and airborne LiDAR for early identification and continuous monitoring of potential rockfalls in the steep cliff area of the Tiejianwan. The findings of this study provide valuable data support for the study of similar disasters in layered red rocks.