Dynamic Stress Accumulation Characteristics in Granite Residual Soil under Cyclic Loading

Dynamic stress is a general mechanics term denoting time-varying stress. In this study, dynamic stress refers to the time-varying internal stress that develops and accumulates within the soil skeleton under cyclic loading, which is distinct from the externally applied cyclic stress in conventional unit-cell tests such as triaxial loading. It plays a critical role in soil deformation under cyclic loading, yet its cumulative characteristics have been insufficiently studied. This paper focuses on granite residual soil, examining the dynamic stress–strain curve’s variation and its cumulative relationship through systematic laboratory cyclic load tests and road model tests. Shakedown theory was applied to quantitatively evaluate subgrade soil stability using the critical stress level ( S L ). Laboratory cyclic load tests reveal that with increasing cyclic loading, hysteresis loops transition from sparse to dense, potentially overlapping, with a progressive reduction in area and shape transformation. The soil exhibits elastic deformation when the hysteresis curve fully closes at the end of a loading cycle. The phase relationship between internal dynamic stress and strain is initially characterized by the strain leading the stress; however, this relationship becomes more complex as the number of cycles increases. A strong linear correlation is observed between dynamic stress amplitude and elastic strain. Road model tests indicate that vehicle speed has minimal influence on residual dynamic stress accumulation, whereas subgrade depth plays a significant role. When the S L is below 40%, the subgrade soil structure remains stable. This study provides valuable insights for road structure design and traffic management planning.