Dimensions of vibration-isolating wall for reducing the ground vibration caused by Shinkansen bullet-train
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 from the cite investigation, it is effective to select the countermeasure by which the vibration in predominant frequency band is effectively reduced. Its effectiveness of vibration-isolating 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 the highly effective vibration-isolating wall considering its materials and dimensions.
Therefore, the model tests focused on the dimensions of the wall were carried out for collection of fundamental data to design the wall in the actual ground. In the experiment, an exciter and a brass plate were respectively used as vibration source and vibration-isolating wall. The model scale was 1/100 of the full size, and a pile foundation was chosen as the foundation type of bridge pier. The following three types of experiments considering the dimensions of the wall were conducted; 1) comparison between the wall width 430mm and 860mm, 2) comparison between the fixing wall and the non-fixing wall, 3) comparison between wall embedment depth of 37.5 mm and 150 mm.
Conclusions are as follows:
1. As the width of the vibration-isolating wall became bigger, the vibration-isolating effect was increased. When distance from the foundation edge to the edge of the vibration-isolating wall (ĶĪL) is short, influence of the wave, which snakes around from a side of the wall, is apparent. When ĶĪL is less than 10m, the influence of the wave snaking around from the side of the wall is large. Subsequently, the effect of vibration reduction increases up to ĶĪL=25m. However, when ĶĪL increases more than 25m, the effect of vibration reduction is hardly shown. Therefore, the vibration reduction using the wall becomes maximum at ĶĪL=25m.
2. When the separate vibration-isolating walls are fixed to be one large wall, the effect of vibration reduction increased comparing with the same size of wall arranged by small separate walls.
3. As the depth of the vibration-isolating wall becomes larger, the vibration reduction effect is increased. The embedment of the wall is important because the effect of vibration reduction appears even in smaller frequency of 30Hz (low frequency band), where the vibration reduction effect was hardly seen in the non-embedment method in which the weight is located on the ground.
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