REDUCTION OF GROUND VIBRATIONS BY IMPROVING SOFT GROUND

Abstract

The countermeasures to ground vibrations generated by car traffic are summarized and among them the detail of the soft ground improvement is described in this paper.The field tests and the finite element analyses were performed on the reduction of ground vibrations by soft ground improvement. At the field tests the ground was improved at region of 20 m in width, 30 m in length and 12 m in depth by lime pile method and the ground vibration test was conducted by using a vibration generator.The finite element analyses were carried out to confirm that the finite element technique is useful to treat the surface wave propagation problem and to develop a prediction method of the reduction of traffic-induced vibration by improving the soft ground.The following conclusions were obtained : i) The improvement of soft ground is effective to reduce the traffic-induced vibrations. The reduction of ground vibrations were observed in the frequency range less than 10 Hz. ii) The width of the improvement area has small influence and the depth of the improvement area and the ratio of rigidity before and after improvement have large influence on the reduction of ground vibrations. iii) The predominant frequency of the ground was slightly increased by the construction of lime piles in the ground. iv) The calculated acceleration by the finite element analysis well agreed with measured values of the field tests. Therefore it is possible to simulate the ground vibration generated by a dynamic load on the ground surface by the finite element analysis. v) The reduction of traffic-induced vibrations can be evaluated by using a prediction figure presented in this paper.