Evolution mechanisms of hydrophobic and dynamic properties in hydrophobically modified silt subgrade subjected to wet–dry cycles and associated damage resistance mechanisms

To mitigate service performance degradation of silt subgrades under cyclic dry-wet conditions, this study employs a nano-superhydrophobic material (NSHM) for hydrophobic modification of silt. A series of laboratory tests, including water droplet penetration test (WDPT), contact angle measurement, dynamic triaxial test, and scanning electron microscopy, were performed on NSHM-modified silt subjected to dry-wet cycles, to systematically characterize its hydrophobic properties, dynamic mechanical behaviors, and underlying modification mechanisms.Results show that NSHM markedly enhances silt hydrophobicity: both WDPT duration and contact angle increase significantly with rising NSHM dosage. At 0.5% content, modified silt achieves a superhydrophobic state, with only 1.1% contact angle reduction after nine dry-wet cycles. The attenuation rate of dynamic resilient modulus decreases progressively with higher NSHM content; the modulus of 0.5% NSHM-treated silt is approximately 20% higher than that of untreated silt after nine cycles. NSHM also alleviates deviatoric stress-induced shear softening and synergistically improves the modulus with confining pressure. A predictive model for dynamic resilient modulus incorporating dry-wet cycles, NSHM content, and stress state is developed and validated. Microscopic analysis reveals that NSHM coats silt particles and fills pore structures, thus enhancing dry-wet damage resistance.