Mechanical and microstructural degradation of pile-surrounding mudstone induced by dynamic pile driving: A multi-scale experimental study

Mudstone's mechanical properties are extremely susceptible to engineering disturbances, and studying the effects of dynamic pile driving (DPD) is crucial for geotechnical stability and pile foundation design. This study conducts a multi-scale experimental investigation, including uniaxial and triaxial tests, and scanning electron microscope (SEM) analyses, to examine the mechanical and structural degradation of pile-surrounding mudstone induced by DPD using an 8.3 t hammer at 1 Hz. Results show that uniaxial compressive strength ( UCS ), elasticity modulus ( E ), internal cohesion ( c ), and internal friction angle ( φ ) decreased by an average of 28.66 %, 41.24 %, 13.12 %, and 56.18 %, respectively. The disturbed mudstone exhibited significant plastic characteristics, with both strain hardening and softening. Multi-scale analyses reveal that cracks and pores increased markedly in number and connectivity, evolving from scattered distributions to dense networks, which closely correlate with the observed mechanical deterioration. Strength reduction varied around the pile, with the least strength loss occurring in the compaction zone below the pile end due to densification from pile penetration. These findings are supported by standard penetration test (SPT) results before and after pile driving, indicating that pre-driving geological surveys overestimate mudstone strength and may pose potential engineering risks. • Demonstrated mudstone weakening from dynamic pile driving, a critical yet overlooked geotechnical issue. • Revealed strength and microstructural degradation of mudstone through integrated macro–micro tests. • Provided new insights for pile design by linking disturbance-induced damage to soft rock foundation risks.