Moisture loss due to evaporation decreases soil cohesion or causes cracks in archaeological sites under excavation or exhibition when the soil is covered with tarpaulins or buildings. Desiccation-induced degradation is difficult to fix; however, effective methods for mitigating evaporation have not been established. This work aims to demonstrate the potential application of sand protection covers to archaeological sites. Coarse sand covers with small water retention mitigate upward porewater transfer as they have small hydraulic conductivity in dry conditions. Evaporation experiments were performed on soil layers with sand covers of four different thicknesses, and the results were simulated with hydro-thermal coupled FE analysis. The experimental results demonstrated that all the 5 mm-thick or thicker sand layers significantly reduced evaporation rate and moderated desiccation cracks, compared to the bare soil case. The numerical simulations calibrated with the experimental data were extended to explore the effects of sand cover thickness. The results showed that the sand cover mitigated the evaporation, and the period of the 1st evaporation stage was extended with increasing sand layer thickness. The required minimum sand cover thickness, defined as the cover thickness that most efficiently reduces cumulative evaporation, was found to have a relationship with the period length of the continuous drying process. That is, the seasonal average rainfall interval of the archaeological site. The proposed protection method is useful to mitigate evaporation-induced damage in soil heritage and has prospective applications for long-term soil moisture retention.
Wo et al. (Thu,) studied this question.