Abstract: Water infiltration and migration in soils are major contributors to geotechnical engineering hazards such as roadbed frost heave and slope instability. As a novel material with excellent performance characteristics,hydrophobic soil offers a promising approach to addressing these issues. To evaluate the water-resisting capacity of hydrophobic soil,this study prepared a hydrophobic soil using Qinghai silty clay and a new hydrophobic additive. A series of experiments—including water droplet penetration tests,immersion tests,breakthrough pressure tests,and nuclear magnetic resonance(NMR)tests—were conducted to systematically investigate the wetting properties,breakthrough pressure,long-term stability,and pore water distribution characteristics of the material. The results indicate that: (1)The water repellency of hydrophobic soil increases with both additive content and compaction degree. The optimal hydrophobic additive content for Qinghai silty clay is 15.5%.(2)Under long-term immersion,the water content-time relationship of hydrophobic soil follows a power function. The infiltration rate gradually decreases and approaches zero,with the final saturation degree stabilizing at approximately 0.2.(3)At the optimal additive content of 15.5% and compaction degree of 0.95,the breakthrough pressure of hydrophobic soil is about 40 kPa. Breakthrough pressure is negatively correlated with pore size and positively correlated with contact angle.(4)After long-term immersion,the pore water content of hydrophobic soil is about 80% lower than that of ordinary soil. Pore water in hydrophobic soil consists mainly of capillary water,accompanied by adsorbed water,distributed in two pore size ranges: 0.01~0.1 μm and 1~4 μm,respectively. This study provides a reference for evaluating the water-resisting performance and supporting the engineering application of hydrophobic soils.