Damage assessment and restoration proposal following the 2023 Türkiye earthquakes: UNESCO World Heritage Site Diyarbakır City Walls, Türkiye

Diyarbakir City Walls, one of the longest defensive structures in the world, following the Great Wall of China, the walls of Antakya, and the walls of Istanbul, is a UNESCO World Heritage site since 2015. With a history of approximately 5000 years, the Diyarbakir City Walls have been affected by consecutive earthquakes centered in Kahramanmaras in 2023, resulting in damages to various sections. Urgent restoration and repair interventions are needed for these sections of the Diyarbakir City Walls due to earthquake-induced damages. Although there are limited studies presenting stone analysis of the Diyarbakir City Walls in the literature, no studies focusing on mortar analysis have been found. The objectives of this study are as follows: (I) to identify the mechanisms and factors of earthquake damages in the Diyarbakir City Walls, (II) to conduct necessary analyses for the selection of mortar materials for post-earthquake repairs, and (III) to provide restoration and strengthening recommendations to ensure the sustainability of the original structure. Observational, petrographic, chemical, and SEM analysis techniques were used, and the findings were interpreted comparatively. The results demonstrate that the most severe damages after the earthquake in the Diyarbakir City Walls were caused by the inadequate adhesion of missing mortar joints and different types of materials used between double-walled structures. Additionally, the presence of clay minerals identified in the mineralogy of the mortar through experimental analysis was defined as an internal issue causing the loss of mortar due to osmotic pressure created by water absorption. Another factor causing the loss of mortar is the presence of chloride-type salts, which were found to be present in a significant amount in all samples and were attributed to the use of Portland cement in previous faulty repairs. It was also determined that recent faulty repointing works contributed to the loss of mortar. Finally, this article presents original restoration and strengthening recommendations to repair the earthquake-induced damages and prevent their reoccurrence in the future.