Naoki Tsukamoto

Countermeasures to reduce ground vibration induced by Shinkansen bullet-train

Hirofumi Toyota

Considering recent speeding up of railway, the ground vibration problems along a railway line have been taken up as a major issue. As a countermeasure to the vibration, it is effective to select the countermeasure by which the vibration of predominant frequency band is effectively reduced. Its effectiveness of vibration-isolating ditch and wall concerning the reduction of the train vibration has become apparent from the theoretical methods and analytical studies using FEM in previous studies. However, it has been still unclear about the actual vibration propagation in the ground and identification of construction method with high vibration damping effect. In this study, we carried out experiments, focused on the spread of vibration generated when passing through the Shinkansen, to grasp the vibration propagation characteristics. Moreover, countermeasure methods to effectively reduce the vibration were discussed.

In this study, we installed a vibration generator as a vibration source, a countermeasure work to reduce vibration, and an accelerometer to measure vibration in the model ground. As countermeasure methods to effectively reduce vibration, a mass body experiment in which heavy objects were loaded on the ground surface, and a vibration-isolating wall experiment in which a vibration isolating material was installed as a wall in the ground were considered. In addition, a reflection vibration experiment to confirm the influence of vibration reflection through the vibration-isolating wall, and a cylindrical vibration-isolating wall experiment where the cylindrical vibration-isolating wall was filled around the exciter or the accelerometer to reduce vibration were also investigated.

In the mass body experiment, a large number of the mass body, in which small lead beads were packed in a square bag of 30 mm, was located on the ground surface. In the vibration-isolating wall experiment, plates of brass and acrylic having a width of 860 mm, a height of 200 mm, and a thickness of 5 mm were installed in the ground with depth of 150 mm. In the reflection vibration experiment, the exciter was put between two brass plates with a width of 430 mm. In the cylindrical anti-vibration wall experiment, a cylindrical brass plate with an outer diameter of 200 mm and a thickness of 5 mm was installed around the exciter or the accelerometer.

Conclusions are as follows: 
1. As a result of comparing the wall materials, the brass plate with higher rigidity than the acrylic plate exhibited greater vibration reduction effect.
2. As a result of comparing the thickness of the vibration-isolating wall, there is not significant influence on the thickness. Therefore, the vibration reducing effect will be exhibited even in thin wall.
3. The vibration reduction effect is greater when the width of the vibration-isolating wall becomes longer.
4. From relation between amplitude rate and the width of the vibration-isolating wall, vibration reduction effect was increased up to 344 mm width of the wall in higher frequency region than medium.