Accumulated plastic strain of natural and stabilized subgrade soils upon cyclic loading: experimental studies and prediction model

This study investigates the influences of static and cyclic stresses on the accumulated plastic strain (ε p) and its intrinsic relationship with shear strength for a natural red clay and a cement-solidified dredge sludge. Through a series of triaxial tests, key findings reveal: (i) Under identical stress conditions, the solidified sludge exhibited 60–70% lower ε p than the red clay, demonstrating that enhanced shear strength fundamentally suppresses plastic deformation; (ii) Critical dynamic stress ratio (i.e. the ratio of the total deviator stress to the shear strength) thresholds of 0.65 for red clay and 0.42 for solidified sludge were identified, beyond which ε p increases exponentially; (iii) Static deviator stress (q 0) dominates ε p accumulation more than cyclic deviator stress (q d), with higher q 0 intensifying the accumulation of the ε p at constant total stress q m (q m = q 0 + q d). To capture these behaviors, a unified prediction model was developed incorporating shear strength parameters, stress states, and stress path length. Model validation shows good agreement with experimental data for both soils, providing a robust framework for predicting subgrade deformation under construction‑phase cyclic loading. The model enables rapid assessment of subgrade performance and evaluation of recycled materials for sustainable subgrade construction in unpaved roads.