Dynamic performance of subgrade structures: an experimental study considering the effects of both static and dynamic stresses

Most existing validations of the resilient modulus are conducted at the material level, leaving a significant gap at the full-scale subgrade structural level. This study integrates full-scale indoor testing, triaxial characterization, and three-dimensional finite element analysis. Tests covered 108 conditions combining three groundwater depths, six static surcharge levels, and six cyclic load magnitudes. Experimental results showed that shallower groundwater increased deflection and reduced subgrade modulus, whereas static surcharge increased modulus. Increasing cyclic loading increased modulus under low static loads but decreased it under high static loads. Using moisture- and compaction-dependent parameters calibrated through triaxial tests, the four-parameter model accounting for combined static and dynamic stresses predicted measured responses more accurately than the NCHRP 1-28A model. These findings extend material-scale model validation to full-scale subgrade structures and highlight the importance of static-dynamic stress interaction in predicting structural responses.