Water retention characteristics of earthen heritage soil during desiccation considering volumetric change

As the most common pathology in earthen heritages, cracking and exfoliation of surface crusts severely threaten their long-term conservation. At present, however, systematic researches regarding the formation and the underlying mechanisms of such deterioration are sufficient. Aiming at the Site of Yar City, which is a World Heritage, free shrinkage tests and mercury intrusion porosimetry tests are conducted on slurry specimens to investigate the pattern of volumetric change during desiccation from both macro- and micro-perspectives. Based on the existing relationship between the gravimetric water content and the matric suction, a revised van Genuchten (vG) soil-water characteristic model with consideration of volumetric change is proposed for the earthen heritage soil. Finally, the water retention characteristics are predicted and analyzed on the basis of micro-pore structure. The results show that the shrinkage characteristic curve of the tested soil slurry has multi-stages. As the water content decreases, the reduction of void ratio is fast at first and then tends to be a gradual stabilization, while the pore-size distribution curve transforms between monomodal and bimodal forms. The obtained dehydrating soil-water characteristic surface can reflect the synthetic influences of matric suction and void ratio on degree of saturation. It is important to quantitatively reveal the drying shrinkage and subsequent cracking behavior of slurry induced by rainfall erosion on the surface of earthen heritages.