Processes of moisture transport in the surrounding rock of Yulin Grottoes during rainfall

Deterioration caused by water transport commonly poses a large threat to culturally-important rock-hewn caves (often called grottoes), affecting the state of wall paintings, sculptures, and cliffs. Even grottoes located in extremely arid areas face these issues. In this paper, we focused on Cave 6 of Yulin Grottoes located in northwest China, which despite being sheltered from direct rainfall ingress still suffers from damp problems. Through multi-scale monitoring and experiments, we identified that air pressure potential and thermal potential are dominant drivers of moisture transport in the surrounding rock. Monitoring at the site scale of 10¹ meters indicated that the water content in the cave ceiling increases during more than 80% of rainfall events, especially during temperature rise and atmospheric pressure fluctuations after rainfall. Large-scale experiments of 10⁰ meters exhibited pore air pressure ascent during rainfall and subsequent temperature rise. Small-scale experiments of 10^− 1 meters demonstrated that pore air pressure has a positive correlation with atmospheric pressure and loading temperature. The process was initiated by rainwater infiltration during rainfall, which triggered the rebalancing of pore air pressure and water content, and was further influenced by post-rainfall fluctuations of atmospheric pressure and temperature rise. We expect these results to support the conservation of Yulin Grottoes, and provide a reference for the conservation of similar heritage sites.