Field monitoring of vibration response of subgrade in a seasonally frozen region

To investigate the dynamic characteristics of ground vibrations induced by moving vehicles in a seasonally frozen region, three field experiments are carried out in the Daqing area of China in various periods throughout the year, in spring, summer and winter, respectively. The results show that: (1) The negative exponent function is employed to fit the vibration attenuation laws of subgrade, and the fitting parameters are provided. (2) The acceleration response amplitudes are influenced by train types, train formation, travel speed and train load together. (3) In the frozen period, owing to the fact that the frozen embankment surface layer increases the rigidity of the system and reduces the energy dissipation capacity, the vibration responses in vertical and longitudinal directions are amplified rather than those in the unfrozen and thawing period. In the same reason, the frozen embankment surface layer certainly restricts the lateral vibration role and reduces its response. (4) In the spring melting period, the permafrost melts in two ways, and there is still a certain thickness of the frozen layer in the middle of the embankment, which will prevent the water content in the embankment surface from penetrating and will melt in spring. So the strength and stiffness greatly decrease, and under the train load, the acceleration amplitudes are reduced in the vertical and longitudinal directions and enhanced in the lateral direction.