Various approaches were tried to prevent the groundwater from encroaching on the carvings, such as digging diversionary tracts, but these efforts were in vain due to the complex water distribution in the mountains.

"It worked on the mountain water on the surface but failed to keep off the water flowing from the distant mountain area," Jiang explains.

It was not until 1992, when they ingeniously came up with the idea of digging holes and tunnels right below the caves to divert water from the temple areas, that the water erosion problems have been effectively addressed.

Since then, they've kept close tabs on any new cracks appearing, the biggest threat to those rock carvings.

"They affect the stability of the rock body," Jiang explains.

The initial observations used rough but ready methods, such as measuring the lengths of those cracks.

In 2015, they started to work on caves where the cracks were classified as hazardous.

"We have to make predictions over the development of any cracks on the cave, like what is the borderline point that would comprise steadiness and under what conditions the cave might collapse," Jiang says.

"It requires calculations, and equipment monitoring and practical experience before coming up with intervention measures and removing the hazards," he says.