Injecting "Black Technology" into Protection of Xi'an City Wall

In recent years, the Xi'an City Wall Management Committee has employed various "black technologies" to thoroughly inspect and protect the City Wall.

Due to the economic and technological limitations, the restoration of the City Wall in the 1980s could not adhere to the strict cultural heritage protection and technical guidance observed today. During that time, there were some specific periods, such as prolonged rainfall, leading to water infiltration, especially in areas with collapsible loess soil. The soil, once saturated with water, would lose weight and subside, causing the upper structures of the city wall to sink and resulting in depressions. Additionally, in the 1930s and 1940s, as well as in the early years of the People's Republic of China, some residents dug holes in the City Wall— some for habitation and others for storage. The prolonged exposure to rainwater could also lead to structural damage.

To protect the Xi'an City Wall more scientifically, the Xi'an City Wall Management Committee was officially established in 2004. A professional team, integrating protection, research, restoration, dissemination, and operational management, began providing more scientific and sustainable protection for the Xi'an City Wall. An innovative exploration of "preventive protection" for Xi'an City Wall has been launched, which pioneers the protection of immovable cultural relics nationwide.

"Black technology" is incorporated into the protection of the City Wall. Building upon traditional restoration methods of "repairing it to match the original", the Xi'an City Wall Management Committee collaborated with over a dozen top domestic surveying and mapping units, including the Department of Geophysics. Drones were used to scan wall defects, and in collaboration with Central South University, they employed ground-penetrating radar and surface wave methods to non-destructively detect hidden dangers, such as voids within the City Wall, achieving a detection accuracy of over 95%.

Through continuous review and reflection on past restoration projects, the Xi'an City Wall Management Committee has implemented a "1+N" inspection model: "1" refers to the cultural heritage department responsible for inspection work, while "N" encompasses all staff of the City Wall management institution, ordinary tourists, and citizens. This enables the management department to promptly identify and address issues. With a sound inspection mechanism, the Xi'an City Wall Management Committee has established over 8,000 digital monitoring points, acting as "stethoscopes" to monitor ancient structures, wall bodies, the surrounding moat, and even the impact of the subway on the City Wall. A "four-color" (green, yellow, orange, red) graded early warning monitoring system was developed, which is a pioneering innovation at home. A judgment mechanism involving experts from multiple industries has also been organized to ensure a clear understanding of City Wall defects, enable prompt responses to various emergencies, and formulate protection plans in the shortest possible time.

In 2021, the Xi'an City Wall was selected as one of the first national pilot units for the preventive protection of cultural relics.