Deterioration investigation and numerical stability analysis of high pedestal in Chinese ancient city towers: A case study of the square wall at the Ming Dynasty Xianling Tomb

Compared to modern buildings, high pedestals are foundational elements unique to ancient Chinese architecture, commonly serving as the structural base for city towers. Constructed from rammed earth and masonry, high pedestals have undergone significant deterioration due to centuries of exposure to natural elements and weathering, compromising their structural stability. There is an urgent need to assess the structural stability of numerous high pedestals to support the effective conservation of ancient city tower heritage. This study integrates a flexible “digital surveying–on-site testing–finite element modeling” workflow tailored to large-scale heritage foundations composed of rammed earth–masonry composites. The Square Wall of the Xianling Tomb serves as the representative case study. A targeted and structure-specific methodological strategy was developed to suit the characteristics of the case. The framework addresses challenges in stability assessment related to multi-material composition, large scale, and concealed damage resulting from long-term settlement. Low-altitude UAV photogrammetry was used to acquire image data of the Square Wall and its surroundings, complemented by on-site surveys to diagnose issues such as cracking and settlement. The results indicate that the foundation remains structurally sound, with measured settlement within acceptable safety limits. Cracking is primarily observed near arch openings due to abrupt stress changes, while the pedestal edges show localized stress concentrations and differential settlement. While masonry degradation leads to general settlement, softening of the rammed earth significantly worsens uneven top-level settlement, posing a major risk to the upper structure. The study also recommends targeted monitoring strategies, providing scientific guidance for the preventive conservation of high pedestals and offering a reference for similar historic structures with comparable damage characteristics. • Integrated 3D data and finite element analysis for stability assessment of high pedestals. • UAV photogrammetry provided precise imaging for damage evaluation and structural modeling. • Masonry deterioration causes overall settlement; rammed earth softening worsens top settlement. • Severe cracking within 60 cm of the top necessitates targeted monitoring and conservation. • Findings guide preventive measures for stability and conservation of ancient structures.