Desiccation of NaCl-contaminated soil of earthen heritages in the Site of Yar City, northwest China

• Exfoliation of surface crusts is a typical type of surface weathering in the Site of Yar City.
• Evaporation tests were conducted on the saturated Yar City soil with different salt contents.
• Cracking behavior of soil closely correlates to the evaporation process and salt contents.

The Site of Yar City (formerly known as the ancient city of Jiaohe) is regarded as the largest, oldest and best-preserved earthen site in the present world. However, during the long-term exposure to the environment, remaining earthen structures suffered serious deterioration caused by many influencing factors. The shallow surfaces of the earthen walls can be fully saturated by the concentrated and heavy rains to form flowing slurry, which will be turned into strongly cracked surface crusts during the following intense evaporation and peeled off by wind deflation. In the meantime, salts could be accumulated in the remains to a quite high content, which could exacerbate the deterioration conversely. In this work, desiccation tests were conducted in laboratory on the initially saturated slurry specimens with different thicknesses and NaCl contents and thicknesses. Development of crack patterns on the surface of the specimen was monitored with a digital camera and analyzed using commercialized software. Results indicated that the evaporation process of NaCl-contaminated specimens could be identified as three stages, which has the same configuration as that of salt-free specimens. Cracking behavior of soil that closely correlates to the evaporation process was also influenced. As the NaCl content increases, the CIF values, intersection number, segment number as well as the total crack length decreases. A non-orthogonal crack pattern and orthogonal crack pattern were dominant for thin and thick specimens, respectively.