How can more than 700,000 “immovable” cultural relics resist the erosion of time?

The third national cultural relics survey shows that there are more than 766,700 immovable cultural relics in my country, including 5,058 national key cultural relics protection sites.

Immovable cultural relics refer to ancient cultural sites, ancient tombs, ancient buildings, grottoes, stone carvings, murals, important modern and contemporary historical sites and representative buildings. Due to the long historical span, diverse materials, and complex preservation environment, the protection of immovable cultural relics has always been a difficult problem in the field of cultural relics protection. How can these sites, which have gone through vicissitudes of life, resist the erosion of time?

Ginkgo leaves to detect water seepage points in Leshan Giant Buddha

At the confluence of the Dadu River, Qingyi River and Min River, the 1,300-year-old Leshan Giant Buddha statue is located. It is 71 meters high, carved into the mountain, and sits majestically overlooking the river, with a solemn and majestic look.

The biggest difficulty in protecting the Leshan Giant Buddha is the problem of water seepage inside the body. In fact, when carving many caves, factors such as ventilation and drainage were considered. In the case of the Leshan Giant Buddha, the ancients designed a scientific and complete drainage system at the beginning of its construction to prevent it from being eroded by rainwater as much as possible.

"A set of ingeniously designed, invisible and interconnected drainage, dehumidification and ventilation corridors were built on the ears, shoulders and chest of the Giant Buddha, which effectively blocked the impact of mountain water seepage on the Buddha." Fan Yuanyuan, director of the Leshan Giant Buddha Grottoes Research Institute, said that the poem by Qing Dynasty poet Wang Shizhen about the Leshan Giant Buddha, "The spring flows from the ancient Buddha's bun," was talking about this drainage system.

However, due to being exposed to the outdoors for a long time, especially being affected by the natural environment, caves such as the Leshan Giant Buddha have become increasingly vulnerable to multiple problems over time, such as structural instability, material deterioration, water erosion, and biological contamination.

"Under the influence of long-term natural environmental factors, a lot of moss and weeds have grown on the face of the Buddha statue. If we are not careful in the maintenance and protection work, it will easily lead to excessive 'protective damage'." said Wang Fengrui, director of the Cultural Heritage Protection Research Institute of China Railway Research Institute (hereinafter referred to as China Railway Cultural Heritage Protection) and director of the Key Research Base of Grotto Temple Cultural Relics Protection Technology of the State Administration of Cultural Heritage.

In response to the internal leakage of the Leshan Giant Buddha, the China Railway Cultural Heritage Protection Team pioneered a fluorescent carbon dot tracing technology, using ginkgo leaves as precursors and preparing carbon quantum dots as tracers on site. By rationally arranging tracer delivery points and sampling points, the seepage path and source of the grotto temple can be precisely detected. The fluorescent carbon dot tracing technology has low cost and high efficiency, filling the technical gap in the field of grotto temple seepage detection and breaking through the technical bottleneck of tracer application in this field. The technical achievements have been successfully applied in the water hazard control work of the Leshan Giant Buddha.

At the same time, the project team used geopolymers to modify traditional pounded plaster materials to carry out refined restoration of stone cultural relics in humid environments, forming a set of key technologies such as cultural relic disease information collection and analysis, non-destructive exploration and micro-damage detection, cultural relic storage environment monitoring and early warning, and shallow surface rock deterioration restoration of grottoes.

Digital technology protects the ancient city of Loulan

The ruins of the ancient city of Loulan are one of the numerous earthen ruins in my country. "Earthen ruins are a world-class problem in the cultural relics protection industry." Guo Qinglin, deputy director of the Dunhuang Academy, believes that earthen ruins are made of earth and are relatively fragile. Most of them are preserved in the open air. Factors such as collapse and weathering can easily lead to their rapid disappearance. Once they disappear, they will not be able to prove the past history. At the same time, according to the principle of minimum intervention in cultural relics protection, many new geotechnical engineering methods cannot be directly adopted.

China Railway Cultural Heritage Protection and the Northwest Institute of Eco-Environment and Resources of the Chinese Academy of Sciences (hereinafter referred to as the Northwest Institute) have developed a set of digital Loulan comprehensive information system. Click on the system to query a lot of information about the Loulan ancient city ruins, including high-precision large-scale remote monitoring of landform and environmental changes around the ruins, real-time automatic monitoring of multi-parameter meteorological conditions, three-dimensional detailed display of the ruins landscape, 720-degree panoramic virtual roaming of the ruins area, and the evolution of the historical administrative area of ​​the Loulan ancient city and related cultural materials.

Taking the recent rescue and restoration of Loulan as an example, in the context of the new era, the China Railway Cultural Relics Protection Team has combined new surveying concepts and technologies to explore a path that fully combines digital technology with traditional cultural relics protection.

The ruins of the ancient city of Loulan are located in an extremely harsh environment, in the Yadan landform with gullies and ravines in the Lop Nur desert, with no human habitation for hundreds of kilometers around. The northeast wind that blows all year round causes continuous wind erosion, and the average number of days with level 8 gale is as high as 80 days per year, and the dust weather is 115-193 days. During July and August, the surface temperature can reach 65 degrees Celsius. Such an environment makes the protection of the ruins of the ancient city of Loulan very difficult. A few years ago, the terrace where the "three rooms and pagodas" in the main ruins area of ​​the ancient city of Loulan were located collapsed, endangering the safety of the main body.

Since 2020, Zhou Peng, head of the Northwest District of China Railway Cultural Heritage Protection, has led the project team to survey and carry out rescue restoration of the Three Houses and Pagoda ruins of the ancient city of Loulan. Through field survey and analysis, team members believe that in extreme climate environments, the best protection is to carry out preventive protection monitoring and monitoring to provide scientific data support for future protection and restoration.

The project team conducted uninterrupted monitoring of environmental factors in the site area, studied wind and sand erosion and site damage patterns, and carried out detailed restoration of the site's main structural damage and surface deterioration. For the first time, they used "sky-air-ground" integrated monitoring and three-dimensional panoramic data collection to establish a simulation model, and integrated the technological achievements into the customized Digital Loulan comprehensive information system. "Digital Loulan" has played an important role in scientific and technological protection and cultural display.

Correction and reinforcement of Kuiguang Pagoda

The Big Wild Goose Pagoda in Xi'an, the Liuhe Pagoda in Hangzhou, the Songyue Temple Pagoda in Dengfeng, the Tiger Hill Pagoda in Suzhou... These well-known ancient brick pagodas are important cultural heritages of my country and even the world, and are also models of ancient high-rise buildings in my country. The protection of these ancient pagodas focuses on tilt correction and disasters caused by earthquakes.

In the south of Dujiangyan City, Sichuan Province, there is a national first-class cultural relic - Kuiguang Pagoda. It is 52.67 meters high and has 17 floors. It is surrounded by Qingcheng, Lingyan and Yulei Mountains on all sides, and the Minjiang River surrounds it, which is magnificent.

Kuiguang Pagoda is a typical example of the tilt correction of ancient brick pagodas in my country in recent years. Due to the use of bricks, the location of the Kuiguang Pagoda on the Minjiang River beach and the high number of floors, the base of the pagoda began to tilt after more than a hundred years. In the early 1980s, the tilt became more obvious. "According to the data at that time, the east and west sides of the bottom of the pagoda were stretched and cracked, and the inclination rate of the tower reached 26‰, which greatly exceeded the 4‰ allowed by national standards." Wang Fengrui said.

Although my country has accumulated some experience and technology in the repair of ancient brick towers, cultural relics restoration experts generally feel uncertain about the highest dense-eaves brick tower in China. In 1999, a team of cultural relics experts from China Railway rushed to Dujiangyan to investigate the geological environment and damage of the Kuiguang Tower. They also proposed a method of coordinated forced landing and lifting for the first time, and performed a "precise correction and reinforcement" operation on the Kuiguang Tower.

Forced landing means digging deeper into the ground, expanding and filling the original foundation, and then using jacking method to straighten the Kuiguang Tower.

The restored Kuiguang Pagoda successfully withstood the 2008 Wenchuan earthquake. It shook but did not collapse, with only structural damage.