FULL 3D SEISMIC RESPONSE ANALYSIS OF UNDERGROUND RAMP TUNNEL STRUCTURE USING LARGE-SCALE NUMERICAL COMPUTATION

摘要

In the Tokyo metropolitan area, long tunnels are being constructed to make a ring road network. These long tunnels need a ramp tunnel which connects the main tunnel located deep underground to ground level. However, ramp tunnels have a complicated structure and their seismic behavior cannot accurately be evaluated by 2D analysis, therefore a precise examination by 3D analysis is required. In the present study we make a detailed model of the soil-structure system of the ramp tunnel and conduct large-scale numerical computation for the 3D seismic response analysis using a dynamic elastic FEM. The major findings are as follows: i) deformation of the ramp tunnel is not accurately estimated by the standard 2D analysis; ii) the seismic response of the main tunnel is small in a hard soil layer and can be evaluated by the standard 2D analysis; and iii) the 3D seismic response of the ramp tunnel significantly changes depending on the characteristics of the input earthquake ground motion.