Nonlinear Creep Model of Railway Subgrade Soil Based on Internal Variable of Crack Density

Aiming at defects of traditional creep models ignoring crack evolution and poorly fitting nonlinear creep of railway subgrade soil, this paper takes silty clay as research object via triaxial and graded loading creep tests. Tests reveal its strain hardening and three‐stage creep behavior dominated by confining pressure‐deviatoric stress coupling. Adopting crack density as core internal variable, fractal derivative, internal variable, and viscoelastic‐plastic theories, a new nonlinear creep model is proposed to describe crack propagation and structural damage. Verified against test data ( R 2 > 0.95), it outperforms the Nishihara model especially for accelerated creep. This study supports long‐term deformation prediction and subgrade design optimization.