Development of an Explicit Model for Long-Term Cumulative Strain in Sand Using Cyclic Triaxial Testing

Wind turbines are subjected to long-term cyclic loading during their service life span, leading to progressive accumulation of deformation, which may compromise the structural integrity and operational safety of the turbines. In China, sandy soils are widely distributed in wind farm construction sites. To investigate the long-term deformation behavior of sandy soils under such cyclic loading conditions, a series of drained triaxial tests are conducted on saturated Toyoura sand, involving both static and cyclic loading modes. The effects of dynamic deviator stress, static deviator stress, and initial confining pressure on the accumulation of strain are systematically examined. Owing to their concise structure and practical applicability, explicit models are frequently employed to represent the long-term cyclic deformation characteristics of sandy soils. Utilizing the results from laboratory tests, this study establishes an explicit formulation tailored to saturated Toyoura sand, capturing its axial strain accumulation under cyclic loading. The corresponding model parameters are also calibrated based on the experimental observations. Two formulations of deviator stress are compared, and the influence of initial consolidation stress and cyclic stress amplitude on deformation accumulation is interpreted from a mechanistic perspective. Comparison with laboratory observations verifies that the model provides a reasonable prediction of the long-term cyclic deformation response in saturated sand.