Identification methods and evaluation metrics for the condition of the Beijing masonry Great Wall

As a great miracle in the history of human civilization, the Great Wall is an outstanding example of a spatial defense system in the world’s cultural heritage. Its heritage protection practice has a profound resonance with Goal 11 of the 2030 Agenda for Sustainable Development, which emphasizes “enhancing the ability to protect cultural and natural heritage” 1 , 2 . As one of the most well-preserved sections of the Ming Great Wall system, the Great Wall in Beijing is experiencing multi-dimensional systematic damage under the combined effects of natural erosion and human activities 3 , 4 . The special structure of the masonry-rammed earth composite structure makes it significantly sensitive to natural forces such as temperature and humidity cycles, saline-alkali erosion, and biological diseases. Related studies have revealed the microcrack expansion and structural performance degradation laws of this type of material under periodic environmental stress 5 , 6 ; at the socio-economic level, the land pressure brought by urban development, the physical impact caused by tourism activities, and the progressive damage of the wall by vegetation roots together constitute a complex challenge to cultural heritage protection 7 . This complex damage mechanism not only threatens the material authenticity of the heritage itself, but also affects the stability of the surrounding ecosystem through the landscape fragmentation effect, forming a dual dilemma between cultural heritage protection and regional sustainable development 8 .