Susceptibility–sensitivity coupled zoning of geological hazards along the Nanjing Ming City Wall

Objective: Existing geological hazard susceptibility zoning cannot directly determine conservation priorities for linear cultural heritage. This study proposes a protection management zoning method that couples geological hazard susceptibility with heritage sensitivity. Methods: Taking the Nanjing Ming City Wall as a case study, landslide and rockfall susceptibility was evaluated using slope units and a combined analytic hierarchy process and information value method, based on more than 110 documents and the results of geological mapping, geophysical exploration, and drilling. Heritage sensitivity was determined according to the distance between the hazard body and the wall, potential movement direction, wall structure and preservation condition, engineering disturbance, and drainage conditions. A 3 × 3 matrix was used to define four protection management classes. The susceptibility zoning was checked through stability calculations for 13 representative profiles, and the coupled results were validated by spatially overlaying 10 existing hazard sites. Results: The 6.773 km² assessment area was divided into 3 high, 7 moderate, 11 low, and 11 non-susceptible subzones, accounting for 0.71%, 4.49%, 9.83%, and 84.95% of the total area, respectively. Under rainstorm conditions, the factors of safety for the 13 profiles ranged from 1.003 to 1.892, with 2 profiles classified as less stable and 4 as basically stable. Of the 21 high, moderate, and low susceptibility subzones, 7, 12, and 2 were classified as having high, moderate, and low heritage sensitivity, respectively. After coupling, Classes I–IV comprised 4, 8, 8, and 12 subzones, respectively. Nine of the 10 existing hazard sites were located in Classes I and II. The protection levels of B3, C1, C2, and C4 increased despite their moderate or low susceptibility because these subzones are adjacent to the wall, their slopes face the wall, or they share the same slope with an enclosing wall. Conclusion: The coupled zoning represents both the conditions for hazard occurrence and the pathways through which geological hazards may affect the wall and its foundation. It provides a basis for inspection, drainage maintenance, deformation monitoring, and mitigation planning.