Prediction of the Effects of Indoor Relative Humidity on Moisture and Salt Migration in Earthen Sites at the Emperor Qin’s Mausoleum Site Museum

Desiccation cracking and salt accumulation are major deterioration mechanisms in earthen sites within site museums, primarily caused by coupled moisture and salt migration under controlled environmental conditions. However, limited research on soil moisture–salt interactions has hindered the development of effective environmental control strategies. This study develops a moisture–salt migration model for the partition walls of Pit 1 at the Emperor Qin’s Mausoleum Site Museum, using the Richards equation and Fick’s law. The model was validated through soil column evaporation experiments and numerical simulations. Simulations over a six-year period under natural ventilation revealed that this condition was ineffective in preventing moisture loss and salt accumulation. While unsaturated humidity control provided short-term delay in deterioration, only saturated humidity (100% RH) effectively prevented long-term moisture loss and salt crystallization. These findings indicate that sustaining a saturated humidity environment is an effective strategy for the long-term preventive conservation of earthen sites.