Located at the confluence of the Dadu, Qingyi, and Minjiang rivers in Sichuan province, the 1,300-year-old Leshan Giant Buddha stands at 71 meters tall. (PHOTO: XINHUA)

By JIAO Yang, LIU Shu, LI Kun & LIANG Yilian

According to the third national survey of cultural relics, over 760,000 immovable cultural relics were examined and registered. The protection of these relics presents a significant challenge due to their historical span, diverse materials, and complex preservation environments.

Faced with these challenges, what measures are needed to combat the erosion of time at some of these historic sites?

Preserving the Leshan Giant Buddha

Located at the confluence of the Dadu, Qingyi, and Minjiang rivers in Sichuan province, the 1,300-year-old Leshan Giant Buddha stands 71 meters tall.

"Compared with the arid and sandy-prone climate in the north, the biggest problem facing the protection of grottoes in Sichuan and Chongqing is shallow surface degradation, water seepage and biological diseases caused by high temperature, humidity and rain," Wang Fengrui, director of the Cultural Heritage Preservation Institute of the China Academy of Railway Sciences told Science and Technology Daily.

The Buddha's construction originally included a sophisticated drainage system to mitigate rain erosion. However, long-term exposure to the natural environment has led to issues such as structural instability, material deterioration, water seepage, and biological damage.

To address water seepage, the team from the Cultural Heritage Preservation Institute of the China Academy of Railway Sciences developed a fluorescent carbon dot tracer technology, to accurately detect seepage paths and sources through strategically placed tracer drop and sampling points.

Digitally protecting Loulan Ancient City

Among China's 767,000 discovered cultural relics sites, soil sites account for one-third. Loulan, an ancient city on the Silk Road, is a notable example. To assist in its preservation, the Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, and the Cultural Heritage Preservation Institute of the China Academy of Railway Sciences have created a digital Loulan integrated information system.

This system provides extensive information on Loulan, including high-precision remote monitoring of environmental changes, real-time meteorological data, 3D landscape displays, a 720-degree panoramic virtual tour, historical administrative evolution, and cultural information. Since 2020, Zhou Peng from the Cultural Heritage Preservation Institute of the China Academy of Railway Sciences and his team have been surveying and repairing ruins in Loulan.

"Now, the protection of soil sites in China has gradually transitioned from rescue protection to preventive protection," said Zhou.

The team continuously monitors environmental factors, studies sand erosion patterns, restores structural and surface damage, and uses "space-earth" integrated monitoring and 3D panoramic data to create a simulation model, all incorporated into the digital Loulan system.

Stabilizing Kuiguang Tower

China's long list of cultural relics boasts over 3,000 ancient towers, with brick structures being the most common. One striking example is Kuiguang Tower in Dujiangyan, Sichuan province. This national first-class cultural relic stands 52.67 meters tall, features 17 floors and weighs 3,460 tons.

Over 100 years, the tower has begun to tilt significantly. "The tower body reached a tilt rate of 26 per mille, which greatly exceeded the four per mille allowed by national norms," said Wang.

In 1999, experts proposed a method to correct the tilt by deepening and expanding the foundation, then lifting the tower. The restored Kuiguang Tower withstood the devastating 2008 Wenchuan earthquake, showcasing the successful integration of traditional craftsmanship and modern technology.