Experimental investigation on the correlation between rainfall infiltration and the deterioration of wall paintings at Mogao Grottoes, China

The Mogao Grottoes is famous around the world for its exquisite wall paintings and colorful painted sculptures, and was inscribed in the UNESCO World Heritage List in 1987. Although the site is located in an arid area, water is still one of the main factors threatening the long-term preservation of cultural relics. The relationship between rainfall infiltration and wall painting deterioration was investigated as part of efforts to develop conservation strategies to prevent deterioration caused by atmospheric precipitation. This was done through artificial rainfall simulation experiments and high-density electrical non-destructive test. Areas prone to wall painting deterioration, as evidenced by periodic condition assessment, showed an association between further deterioration and natural heavy rainfall. The results show that the covering layer above the grottoes has a small runoff coefficient, and the rainfall infiltration is much larger than the volume of runoff produced. The rainwater migrates preferentially along the rock fractures in the form of gas or through the gaps between the grotto eaves and the rock, or through cracks in the form of liquid. This is the main mechanism for activation of salt damage and deterioration of the wall paintings. The covering layer above the grottoes is thin, and the through-cracks in the surrounding rock or external wooden eaves are particularly vulnerable to rainfall infiltration. This indicates that more attention should be paid to the system of preventive protection by rainwater disposal. This research has important practical value in improving preventive protection of the Mogao Grottoes.