Research on dynamic characteristics of high-speed railway subgrade with AB group filler based on in-situ excitation test

The dynamic stability of the high-speed railway subgrade is crucial when subjected to long-term cyclic loading. To investigate its dynamic response characteristics, in-situ excitation tests were carried out based on actual work sites, the evolution of the natural frequency, and the dynamic shear modulus ratio of the subgrade under cyclic loading, while the Critical Slowing Down (CSD) theory was explored. The test results show that the Peak Ground Acceleration (PGA) gradually decays with the increase of horizontal and vertical distance, with a decay degree of 90% as the standard, the dynamic influence range of the surface and interior is mainly within 2.9 m and 3.7 m respectively. Dynamic stresses decay with increasing vertical distance, but the effects of frequency and torsion are small compared to the acceleration response. With the increase of horizontal and vertical distances, the ratio between the natural frequency and dynamic shear modulus gradually increases, and the natural frequencies at the center of vibration and farther away are located around 14–16 Hz and 17.5–23 Hz, respectively. By utilizing the critical slowing theory, the correlation between variance, autocorrelation coefficients (AC), and the time-course data of dynamic stress was examined, and the results show that the CSD theory can be used for the stability performance analysis of the subgrade.