Salt distribution of earthen heritage site wall and its mechanism in northern China

Salt damage is one of the most important causes of the destruction of earthen heritage sites. The study of salt distribution is of great significance for identifying potential erosion patterns of earthen heritage sites. In previous studies, the salt distributions in only a few earthen heritage sites have been analysed. In this study, 35 typical earthen heritage sites in northern China were investigated that are more widely distributed and more universal than those in previous studies. The salt content and natural water content at different locations on the earthen wall were compared, and the differences in the soluble-salt distribution for different regions of northern China were explored. The results show that the salt content of the loose layer was higher than that of the surface crust, except in the Subash Buddhist Ruins. The difference for the Subash Buddhist Ruins may be the special dual-porosity structure with inter-aggregate pores (large pores) and intra-aggregate pores (small pores) in the coarse-grained soil. The threat of soluble salt to earthen heritage sites in northeast China was found to be far less than that in northwest China, which may have been caused by different rainfall and evaporation intensities. Finally, the reasons for the salt distribution, the prevention of salt damage, and the application of the results to earthen heritage sites in northern China were examined.