The serious damage caused to various earth structures by the Hyogo Prefecture Southern Area earthquake highlighted a number of problems with the earthquake-resisting performance of existing embankments. Earth structures, which feature a long and narrow construction, require effective reinforcement work and a simple method to evaluate the earthquake-resisting performance.
Against this background, the RTRI proposed a simple technique to evaluate the necessity of reinforcement work and proposed a map for use in selecting damage-apprehended areas. The technique to evaluate earthquake-resisting performance is established on the basis of surveys on the disaster caused by the Kanto Great Earthquake and the above-mentioned earthquake in Hyogo Prefecture, the relationship between the principal dimensions (structure type, height, gradient, etc.) and damage of earth structures, and the susceptibility of the ground to vibration (Fig. 1). Damage-apprehended areas are extracted according to the predicted ground vibration caused by the assumed earthquake motion. Figure 2 shows a map used to select areas where a seismic intensity of six or over is anticipated for four earthquakes assumed by the Prime Minister's Office, each with its epicenter in the Metropolitan area (Fig. 2).
By applying this technique, it is possible to easily evaluate the earthquake-resisting performance of earth structures based on their type and configuration and clarify the priority order of reinforcement work.