Cave No 168 is one example and it took three years to finish reinforcement procedures.

The Institute of Geology and Geophysics, the Chinese Academy of Sciences, was invited to survey the land first before operations were carried out.

"The theoretical calculation alone is not enough, since many problems can arise during practice," Jiang says.

For example, exactly how much grouting pressure should be applied to fill the cracks in the rocks needs constant experimentation.

"If it's too small, it can't reach certain fine cracks, but if it's too big, new cracks will open," Jiang says, adding that the time for the grout to solidify between the rocks also needs to be observed and modified.

Cave No 168 has had a concrete beam and bolt system placed to secure its thin roof, while an advanced electronic monitoring system has been installed to keep track of changes, such as crack growth, wall pressure and air, over the following five years in the cave.

All the data are transported to an electronic monitoring center at the Academy of Dazu Rock Carvings.

The center was established in 2012 and has been equipped with the advanced monitoring system since 2019. It has received data on 70 indicators of artifacts and surrounding environment from all major stone carvings protection sites across Dazu.