Growth Process and Characteristics of Drying Cracks on the Soil Surface of Yangguanzhai Site Cemetery During Archaeological Excavations.

The primary challenge for the earthen sites of great historic and scientific value in China is attributed to drying cracks. We investigated 105 exposed partial-cave tombs in the Yangguanzhai Site Cemetery to understand drying cracks' growth process and characteristics. Real-time monitoring and observations were further conducted toward one specific tomb during archaeological excavation for finer-grain records. Results show that these cracks grew rapidly on the soil surface during the early stage of the excavation and some then transformed to more severe deterioration, such as gullies and collapses. Intriguingly, most drying cracks found on the side surface grew initially from top areas and extended downward vertically and independently. By contrast, their counterparts on the bottom surface were curved and twisted with one another. The changes of the soil properties and water content in soil at different depths suggest that larger porosity and smaller-size soil particles facilitate faster water absorption and evaporation of superficial soil, whereas low rates of water evaporation and soil desiccation on the flat bottom surface slows down the formation of drying cracks. Further investigations and field experiments are the next steps in building complete growth models of drying cracks and fully understanding the underlying mechanism. [ABSTRACT FROM AUTHOR]