Characteristics of dynamic response of the active layer beneath embankment in permafrost regions along the Qinghai–Tibet Railroad

Dynamic response characteristics and stability of embankment are of primary importance for railroad operation in permafrost regions. The strong motion tests are carried out on a traditional sand gravel embankment at the Beilu River segment along the Qinghai–Tibet Railroad, and the acceleration waveforms at the shoulder and the slope toe of the embankment, when passenger train and freight train pass, are collected through strong motion tests. There is an obvious attenuation effect during the waveform transfer process from the shoulder to slope toe, and the natural frequency of the embankment is between 30–40Hz. Based on the tests in situ, the nonlinear dynamic finite element analysis is applied for numerical simulations on dynamic response of the traditional sand gravel embankment to train load, and the influences of underlying active layer on the dynamic response of the embankment at different seasons are analyzed. The results show that the vibration attenuation of the train load is obvious at different seasons, which presents a linear decrease tendency in summertime, but a nonlinear decrease tendency in wintertime. Both of the two decrease tendencies mainly occur within the soil layer above the permafrost table, but the attenuation effect in summertime, when the active layer is thawed, is slightly greater than that in wintertime when the active layer is frozen. Soil deformation induced by train vibrations occurs mainly above the permafrost table in summertime, but in wintertime, it mainly occurs above the natural surface. Meanwhile, the amount of deformation at the same location in summertime is far more than that in wintertime.