Identification and Risk Assessment of Erosion Characteristics of the Rammed-Earth Great Wall from the Perspective of Preventive Conservation

Abstract. The rammed-earth Great Wall, a vital world heritage site, faces rapid erosion exacerbated by environmental change, demanding urgent erosion assessment as foundational conservation work. From a preventive conservation perspective, this paper develops an integrated digital 'census-quantification-assessment' methodology to systematically analyse rammed-earth wall erosion characteristics and enable risk assessment. Utilizing unmanned aerial vehicle (UAV) photogrammetry, comprehensive high-precision 3D modeling and multi-temporal imaging of the Ming Great Wall is achieved. This establishes a dynamic digital twin model, revealing the characteristic deterioration sequence of 'bottom hollowing → local collapse → overall destabilisation'. Quantitative morphological indicators (hollowing height, depth, area, rate) combined with 3D point cloud analysis map the evolution of wall-base hollowing within the digital twin. Integrating these morphological metrics enables the proposal of an erosion risk grading system, allowing precise location and dynamic monitoring of risks within individual wall sections. Compared to traditional approaches, this framework provides a data-driven decision basis for preventive protection. It implements a 'monitoring-assessment-warning' closed-loop management strategy applicable to the Great Wall and similar linear heritage. This promotes a shift in conservation strategy from post-event restoration towards proactive risk prediction, supporting the development of a holistic, lifecycle cultural heritage risk management system.