The earthquake (Mw 7.3) that struck Nepal on April 25, 2015 caused damage to many civil engineering and architectural structures. While several road gabion retaining walls in mountainous regions incurred damage, there was very little information that could be used to draw up earthquake countermeasures in Nepal, because there have been few construction cases or case studies of gabion structures, nor have there been experimental or analytical studies on their earthquake resistance. Therefore, we conducted a shake table test using a full-scale gabion retaining wall to evaluate earthquake resistance. From the experiments, it was found that although gabion retaining walls display a flexible structure and deform easily due to the soil pressure of the backfill, they are resilient structures that tend to resist collapse. Yet, because retaining walls are assumed to be rigid bodies in the conventional stability computations used to design them, the characteristics of gabions as flexible structures are not taken advantage of. In this study, we propose an approach to designing gabion retaining walls by comparing the active collapse surface estimated by the trial wedge method, and the experiment results obtained from a full-scale model of a vertically-stacked wall, which is a structure employed in Nepal that is vulnerable to earthquake damage. When the base of the estimated slip line was raised for the trial wedge method, its height was found to be in rough agreement with the depth at which the gabion retaining wall deformed drastically in the experiment. Thus, we were able to demonstrate the development of a method for evaluating the seismic stability of gabion retaining walls that takes into consideration their flexibility by adjusting the base of the trial soil wedge.
Seismic stability evaluation of volcanic soil at Takanodai, Minamiaso village, Kumamoto
