# Early Detection and Stability Assessment of Hazardous Rock Masses in Steep Slopes
###### Abstract  
The assessment of slope stability plays a critical role in the prevention and management of slope disasters. Evaluating the condition and stability of hazardous rock masses is essential for predicting potential collapses and assessing treatment effectiveness. However, conventional measurement techniques are inadequate in high slope areas, which lack sufficient spatial data to support subsequent calculations and analyses. Therefore, this paper presents a method for the early identification and evaluation of unstable rock masses in high slopes using Unmanned Aerial Vehicle (UAV) digital photogrammetry and geographic information technology. By considering nine evaluation indices including geology, topography, and induced conditions within the study area, weights for each index are determined through an analytic hierarchy process. A semi-automatic approach is then utilized to extract and analyze rock mass stability. The reliability of this early identification method is confirmed by applying the limit equilibrium principle. The findings reveal that 17.6% of dangerous rock masses in the study area fall into the unstable category (W4, W6, W10). This method effectively assesses slope rock mass stability while providing technical support for disaster monitoring systems, warning mechanisms, and railway infrastructure safety defense capability to ensure safe mountain railway operations.  
high gradient slope; mountain railway; hazardous rock formation; preliminary assessment; stability analysis +
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use of 3D laser technology allows for quick acquisition of 3D coordinate data from object surfaces through laser scanning but comes at a relatively high cost [15; 16]. When UAVs are used for safety investigations on high steep slopes, a single data acquisition scheme results in low equipment efficiency or model accuracy, especially in high steep slopes where image distortion may occur [17; 18; 19].  
To address these issues, this study proposes a method for processing UAV point-cloud-based early identification of dangerous rock masses on high slopes which fully utilizes the UAV model to analyze and extract useful information enabling early identification.  
In the field of dangerous rock engineering on high slopes, there are two main stability evaluation methods: the limit-equilibrium-theory-based analysis method and numerical simulation [20; 21; 22; 23]. Currently, the stability evaluation method based on the limit equilibrium theory lacks a relatively complete index system [23; 24; 25; 26]. The numerical simulation method considers slope failure mechanisms more realistically [27; 28]; however, later numerical simulation methods take into account complex stress-strain relationships within rock materials making calculations more complicated with less practical application [29; 30]. It is challenging to apply continuous deformation analysis methods to dangerous rock masses found in high slopes, creating a gap between models and practice [31; 32; 33; 34]. Although finite element software currently includes crack simulation units, when numerous cracks exist, there are usually restrictions such as no rotation due to small displacement limitations present [35; 36; 37].  
Given these limitations, this study proposes a stability evaluation method for dangerous rock masses found in high slopes based upon UAV digital photogrammetry technology. Utilizing UAVs for on-site aerial surveys to extract topographic data enables the early identification of potential hidden danger zones. Establishing a reasonable system of stability evaluation indices facilitates rapid and accurate assessments of site stability.