sulfate migration pattern after repairing the Ming Great Wall

Salinity deterioration is one of the most critical factors contributing to the degradation of pre- and post-rehabilitation earthen sites in Northwest China. This study utilized hemp-cut fiber-modified soil, a common material in restoration projects, to investigate the water and salt migration patterns of earthen sites after restoration and to clarify the mechanisms of salt deterioration in restored earthen sites. The migration rates and pathways of sodium sulfate in earthen sites before and after restoration are quantified by remodeling site soil specimens and restoration simulation specimens to clarify migration mechanisms from a microscopic perspective. The test results indicated that the rate of salt accumulation in the earthen sites significantly decreases, and the rate of salt damage slows after restoration with hemp-cut fiber-modified soil. Due to the rapid salt accumulation rate at the repair's edge, the hemp-cut fiber repair layer exhibits severe cracking. Although the rate of salt migration in each component changes after restoration, the migration pathways remain fundamentally the same. Under capillary action, the salt ascends to the maximum height along the edge. Then, the primary migration mode shifts to horizontal diffusion, accelerating the salt accumulation rate in the central area. Simultaneously, as salt accumulates at the top, the influence of gravity increases. More salt migrates downward, ultimately enriching the middle and upper layers of the site. This study can provide a reference for protecting against salt damage in earthen site restoration and for selecting and revising restoration materials.