The Effect of Seismic Stability of Retaining Wall on Seismic Earth Pressure

Abstract eng:
In recent years, there has been serious damage to retaining walls (RWs) because of large earthquakes. Seismic earth pressure, which is one of the important external forces acting on RWs during an earthquake, is largely affected by the dynamic interaction between the wall and the backfill; the detailed mechanism of this effect has not been clarified well. In the current seismic design procedure, the Mononobe-Okabe theory is often used for evaluating the seismic earth pressure. Although this theory is simply based on the pseudo-static approach, many researchers have mentioned that this theory is applicable under a small seismic load (around 200 gal). In this study, therefore, a series of shaking table model tests were performed to investigate the effect of seismic stability (bearing condition) of the RW on seismic earth pressure. The experiment was conducted for four cases (Case1 - 4). A RW model that was either completely fixed or elastically supported was used in all cases except for Case 4, in which a gravity-type RW model (one-tenth scale) was used. The RW model used for Cases 1-3 were made of aluminum and were 715 mm high and 40 mm thick. Two-component load cells which can measure both the normal and shear component of seismic earth pressure were positioned at nine locations in the direction of the height on the RW surface. The gravity-type RW of Case 4, on the other hand, was 530 mm high, and twocomponent load cells were positioned at 10 locations in the direction of the height and at six locations on the bottom surface of the RW footing. The model used for Cases 1-3 did not simulate the actual RW; in fact, these model experiments were conducted under more simplified conditions in order to evaluate the impact of the seismic stability (bearing conditions) of the RW on the seismic earth pressure, with the focus on obtaining accurate measurements of seismic earth pressure. On the other hand, in Case 4, the focus was on simulating the seismic earth pressure acting on the actual gravity-type RW, where the model specification (height, width and center of gravity) and the yield seismic intensity was set as similar as possible to those of an actual RW. The experiments revealed that the seismic earth pressure (intensity, phase property, distribution) is largely affected by the seismic stability of the RW. By considering the dynamic response of RWs, the seismic earth pressure under large earthquake loads can be calculated more rationally than by the Mononobe-Okabe theory. This result have already applied to the seismic design procedure of retaining structures under large earthquake, which is written precisely in the new design standard of railway retaining structures in Japan (2012).

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