1. Evaluation of Earthquake-resistance Performance and Measures against Earthquake of Under-track Transversal Structures

  • Understanding how the influence of under-track transversal structures on the surrounding ground and their earthquake-resistance performance differ greatly depending on their method of construction.
  • Clarification of the efficient range and level of ground reinforcement for different construction methods as earthquake-resistance measures.

Different construction methods have been put to practical use for under-track transversal structures. These include the open-cut method that involves cutting the ground and constructing caissons while temporarily supporting the track with beams, and the trenchless method involving the insertion of one element into another in succession. With the present earthquake resistance calculation method, however, performance is examined for a structure that has been completed. As this does not consider different construction methods, earthquake-resisting performance is not evaluated to satisfy the practical conditions.

In consideration of the features of the open-cut and the trenchless methods, the effects of each construction method on the surrounding ground therefore are evaluated through model vibration tests and numerical analysis based on the survey results of existing structures. The results showed that soil rigidity dropped to about 20% of the initial value at the side of the structure in the range of the angle of repose of soil from the tip of pile excavating earth in the case of the open-cut method; and to about 10% around the element (approximately in the range equivalent to the element diameter) in the case of the trenchless method (Fig. 1).

It is confirmed that there were no differences in the external force that acts during earthquake between the two construction methods, which is almost the same value as considered in the present design standard. This demonstrates that the structures have no problems in terms of strength. However, the open-cut method has 20 to 30% larger deformation due to shearing and rotation than that of the trenchless method in earthquake because of deterioration of the soil rigidity in wider range. It also shows that the ground settlement is big and its area is wide at the boundary between the ground and the structure (Figs. 1 and 2).

Based on these findings, it is concluded that reinforcement of the surrounding ground is an effective anti-earthquake measure, and proposed a method to determine the range and the degree of measures for the open-cut and trenchless methods.

Fig. 1 Loosening conditions of the ground and an outline of the range and the degree of ground settlement in an earthquake.
Fig. 2 Degree of settlement of the backside ground in an earthquake at the boundary between the ground and the structures

R&D > Major Results of Research and Development in Fiscal 2006 > I Safety/Reliability


Copyright(c) 2007 Railway Technical Research Institute, Tokyo Japan, All rights reserved.