Effects of Loading Frequency on the Dynamic Response and Pore Structure of Silty Clay under Repeated High-Amplitude Loading

<title>Abstract</title> <p>The dynamic response of silty clay in unpaved roads is affected by the duration of wheel loading, but the role of loading frequency remains insufficiently understood. This study investigates the effects of loading frequency on the progressive plastic deformation and the pore structure of silty clay under repeated high-amplitude loading and low confining pressure by cyclic triaxial tests and Mercury intrusion porosimetry (MIP) tests, respectively. The results show that a higher loading frequency reduces accumulated plastic strain, and the reduction from 0.1 to 1.0 Hz is more pronounced than that from 0.01 to 0.1 Hz. A higher loading frequency produces a higher resilient modulus and lower cumulative energy dissipation. The MIP results indicate that cyclic loading mainly alters macro-pores and meso-pores, whereas micro-pores remain comparatively stable. Macro-pore volume decreases with increasing accumulated plastic strain, and part of the macro-pore space is transformed into meso-pores. Lower loading frequencies prolong the duration of stress action within each cycle, thereby promoting more sufficient pore-structure rearrangement and compression. The fractal dimension results further show that cyclic loading increases the heterogeneity of macro-pores but simplifies the meso-pore and micro-pore structures. These findings provide a microstructural basis for evaluating frequency-dependent deformation of silty clay in unpaved roads.</p>