The recurrent crystallization and subsequent volumetric expansion of soluble salts pose significant risks to earthen sites, particularly those with archaeological remains on their surfaces. Therefore, timing interventions based on salt content is crucial. This study focuses on the effects of soluble salt content on the earthen site within the burial pits of the Qin Mausoleum, with a particular emphasis on defining safe salinity levels. A mixture of Na2SO4/NaCl salts in a 1:1 mass ratio was added to remodelled soil cakes, which were then aged in a climate chamber for several months. The area of salt expansion on the soil cakes' surfaces was measured using a deep-focus microscope to assess damage. The results indicate a sudden increase in salt expansion when salinity exceeded 0.1%. Additionally, re-evaluations of these soil cakes years later allowed for the exploration of mechanisms and the feasibility of assessing soil surface expansion and friability at different stages of the earthen site's lifecycle, including excavation and display. These findings provide preliminary scientific bases and novel methodologies for the further preventive conservation of heritage earthen sites.

The solid waste soda residue (SR) exhibits a high content of soluble salts, and the liquid phase soluble salts in soda residue soil (SRS) undergo phase transition crystallization during cooling process, leading to subgrade salt expansion and deformation damage. In order to explore the salt mechanisms of SRS, this paper systematically analyzes the impact of SR content on the salinization and salt expansion characteristics of SRS using soluble salt tests and salt expansion experiments. Combined with X-ray diffractometry (XRD) and low-temperature frost shrink tests, the study analyzed the salt expansion process of SRS. The results indicate that under different SR content, SRS is classified as chloride saline soil. The SRS is categorized into weak saline soil, moderate saline soil, strong saline soil, and over-saline soil with different soda residue dosage. During cooling from 20 degrees C to -25 degrees C, all SRS groups exhibit initial salt expansion followed by frost shrink deformation characteristics. As the SR content increases within the 0 % - 40 % range, the temperature range for severe salt expansion gradually decreases from 5 degrees C to -15 degrees C. At 25% SR content, SRS exhibits the most severe salt expansion, while excessively high SR content inhibits the crystallization of sulfate salt phase transitions. The study identifies three stages in the salt expansion process of SRS: promotion stage, severe stage, and inhibition stage. The research findings provide valuable insights for the prevention of salt expansion in SRS and the widespread utilization of SR in road applications.