Preventive Protection of Earth Heritage: Influence of Silane Application Methods on Surface Effectiveness of Consolidation– Pingyao Rammed Earth Wall, a World Heritage Site

The surface soil at rammed earth sites exhibits low mechanical strength, high water susceptibility, and prevalent soil stripping deterioration.These deteriorating conditions urgently require preventive stabilization measures.This study, focusing on the rammed earth inner walls of Pingyao Ancient City — a UNESCO World Heritage Site, evaluates the critical role of application methods in earthen site conservation by comparative analysis of surface-reinforced specimens treated with four silane coupling agents and three application methods. Hydrophobicity, water resistance, and mechanical property variations were systematically assessed to elucidate method-dependent efficacy. Adhering to the <i>repairing the old as old</i> principle, colorimetric variation and permeability analyses were conducted. Microstructural and pore characteristic alterations after reinforcement were further investigated through scanning electron microscopy. Results indicate that spray-reinforced specimens exhibited optimal performance among all four materials, demonstrating uniform reinforcement efficacy, maximal water resistance, minimal chromatic and permeability deviations. Capillary absorption reinforcement, while yielding limited surface hydrophobicity, enhanced internal structural integrity via capillary-driven material migration, achieving balanced permeability and mechanical improvement. These findings underscore spray reinforcement as the premier strategy for surface protection, whereas capillary absorption proves viable for subsurface consolidation in some constrained engineering contexts. This study produced weathering-like soil specimens to simulate the highly weathered rammed earth surfaces.This study focused on the influence of the application method on the consolidation effect with different silane coupling agents.Spraying can better utilize the good water repellency of silane coupling agent with long chain.SEM observations further demonstrated the effect of application method in microscale. This study produced weathering-like soil specimens to simulate the highly weathered rammed earth surfaces. This study focused on the influence of the application method on the consolidation effect with different silane coupling agents. Spraying can better utilize the good water repellency of silane coupling agent with long chain. SEM observations further demonstrated the effect of application method in microscale.