Use of geosynthetics to improve seismic performance of earth structures

Abstract

After reviewing seismic performance of earth structures based on case histories in Japan and relevant model test results, advantages of using geosynthetics in improving their seismic performance are demonstrated. As one of the successful applications, geosynthetic-reinforced soil retaining walls are highlighted, focusing on several influential factors such as facing rigidity, arrangement and properties of reinforcements, and backfill and subsoil conditions. In addition, further applications of the reinforcement method using geosynthetics are introduced, which include combination with other reinforcement methods, application to bridge abutments and piers, and application to ballasted railway tracks.

Introduction

Fig. 1 shows global distribution of earthquake epicenters that took place during a ten-year period from 1990 to 2000 with magnitudes equal to or exceeding 4.0 and epicentral depths of 50 km or less. As indicated by an arrow in the figure, Japan is located in a very highly active zone of such seismic events.

Table 1 summarizes the peak values of horizontal ground accelerations (PGAs) and velocities (PGVs) that were recorded during recent major earthquakes in Japan. After the 1995 Hyogoken-nanbu earthquake, the availability of strong motion data recorded near the epicenter was improved significantly. Therefore, at some of these sites the PGA approached or exceeded 800 gals and/or the PGV exceeded 100 kines.

On the other hand, earth structures, such as embankments as schematically shown in Fig. 2a & b, have been widely employed to construct highways, railways, river dikes and housing lots. In addition, in order to reduce the area to be occupied by the construction of embankments and thus the volume of fill material, retaining walls (RWs) have also been frequently adopted, as schematically shown in Fig. 2c & d.

If we convert the horizontal seismic inertia and vertical gravity vector into a resultant pseudo-static force as schematically shown in Fig. 3a, the direction of apparent gravity will be inclined. Then, the driving moment to trigger the sliding failure along a potential failure plane will be increased, as shown in Fig. 3b. Under such circumstances, adding reinforcements in the embankment with their tensile forces mobilized effectively will increase the resisting moment, as shown in Fig. 3c.

In view of the above, by addressing the following questions in this paper, attempts are made to share Japanese experiences on the use of geosynthetic-reinforcement to improve seismic performance of earth structures:

• How different are the seismic performances of earth retaining structures with/without geosynthetic-reinforcement?

• What are the influential factors in improving effectively the seismic performance of earth retaining structures using geosynthetics?

• How can we extend the application of geosynthetic-reinforcement technologies to other types of earth structure?

In order to answer the above questions, the paper begins with a review of seismic performance of earth structures in Japan. Next, influential factors in improving seismic performance of retaining walls using geosynthetics are discussed. Some of further applications of geosynthetic-reinforcement are briefly reviewed as well, which are followed by conclusions.