Effects of the Ground Reinforcement on the Dynamic Behaviors of Compacted Loess Embankment with Ballasted Track

An embankment is needed to satisfy the requirements for the longitudinal slope of railway lines, and ground reinforcement is also generally required in loess regions. The present study attempted to understand the effects of different ground reinforcement measures on the dynamic characteristics of a track–embankment–ground system. To this end, the critical speeds and the distributions of dynamic stress and environmental vibration were analyzed using a 2.5D finite element method. Three typical ground reinforcements, including dynamic compaction ground (DCG), soil–cement compacted pile composite ground (SCG) and CFG pile composite ground (CFGG), were used. The results indicate that the train speed (critical speed I) at which the maximum vertical displacement of the track occurs is universally higher than that (critical speed II) at which the wave propagation phenomenon occurs. The lower boundary limit of the peak region in the dispersion relationship can be selected as the reference value of critical speed II. Moreover, the values of critical speed I obtained using the DCG, SCG and CFGG models were around 92, 105 and 127 m/s, respectively. For critical speed II, the values were 75, 80 and 115 m/s. Once the train speed exceeded critical speed II, the vibration was confined to the embankment in the CFGG model, as evidenced by the isolation of the wave propagation from the embankment to the ground as well as the increasing dynamic stress in the embankment. After reinforcement, the dynamic stress, dynamic influence depth (DID), critical speed and resonant frequency increased. Additionally, the DID stayed around the 3–6 m range at all speeds.

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