Resilient characteristics and prediction model of subgrade filler under graded variable confining pressure with variable dynamic load

The novel prestressed railway subgrade (PRS) is applicable to both existing subgrade reinforcement and newly-built subgrade construction. The resilient modulus (M_R) is a key indicator of subgrade stiffness. To evaluate the stiffness enhancement induced by horizontal prestress, dynamic triaxial tests were performed on silt filler under graded constant confining pressure with variable dynamic load (GCCP–VDL) and graded variable confining pressure with variable dynamic load (GVCP–VDL) modes. The effects of initial confining pressure (σ_3ini) and confining pressure increment (Δσ₃) on M_R were investigated, and an M_R prediction model for GVCP–VDL cases was developed. The results show that staged variable confining pressure (σ₃) significantly increases M_R, suppresses inter-particle slippage, and stabilizes the soil skeleton. This effect is more pronounced under saturated moisture (w_sat) cases. Increasing σ_3ini enhances deformation resistance and M_R, improves specimen stability, and delays dynamic failure. In some cases, it even shifts the response from failure to stable behavior. Under GVCP–VDL cases, M_R increases with Δσ₃. Therefore, horizontal prestress should be applied in stages according to the subgrade service state. Increasing σ₃ raises the critical dynamic stress and helps prevent instability under excessive train loads. An M_R prediction model for GVCP–VDL cases was proposed and validated using the experimental results. These findings provide guidance for the structural design and service performance evaluation of PRS.