In the 2015 earthquake in Gorkha, Nepal, damaged different kinds of structures around the Kathmandu Basin. On the other hand, in mountainous areas, it was confirmed that gabion structures such as retaining walls along roads showed their high flexibility by performing their functions. In this paper, based on the results of the damage field survey on gabion retaining walls, a full-scale shake table test is conducted to evaluate the earthquake resistance of gabion retaining walls on roads, which are a common site in Nepal. The soil container used for the full-scale shake table test has the following internal dimensions: 4.0 m height, 3.1 m width, and 11.5 m depth. Earthen bank retaining walls with height of 3 m were arranged in three rows in a perpendicular direction to the cross-section, and the ground behind the retaining wall was prepared. The sinusoidal waves of 3 Hz were applied, consisting of 2 s of gradual increase, 4 s of steady part, and 2 s of gradual decrease; the input waves were provided in four stages of acceleration amplitude. Three types of gabion retaining walls were considered, i.e., vertical-type, stepwise-type and gravity-type, and 3D terrestrial laser measurement was conducted before and after shake table test of each case. Comparison of the residual deformations of the gabion retaining walls measured by 3D terrestrial laser showed that the vertical-type wall did not collapse but tilted forward after the shake teble test. A similar damage situation was confirmed by the field survey in Nepal. The other two cases suffered only slight deformation and are considered to be effective structures for application on sites. Finally, the trial wedge method was applied to the experimental results of the vertical-type of gabion retaining and useful suggestions for future earthquake-resistant design were made by comparing the active collapse angle with the positions of deformation, such as cracking which occurred in the ground behind the retaining wall after shaking. Then, the applicability of trial wedge method and its problem in the design of gabion retaining wall were shown.

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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.

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