Many masonry walls have been constructed on slope along the Japanese railway. These walls are used as a surface protection on cut slopes and as retaining walls on embankments. Since these masonry walls are more brittle than the concrete retaining walls, the risk of collapse of masonry walls due to earthquake is high. For this reason, in order to improve railway safety against earthquakes, the reinforcement of masonry walls is required. Therefore, we develop a seismic reinforcement method for masonry walls and confirmed its effectiveness by centrifuge model experiments. The reinforcement method mainly consists of the penetration of the nailing into the slope and the solidification of the gravel backfill by the grout injection. As the result of the shake table experiments in the centrifuge, we confirm that the reinforced masonry wall does not collapse even under the shaking with a maximum acceleration greater than 1000 gal.

1 Introduction
1.1 Background

There are a lot of masonry walls (Fig. 1) that have constructed on slopes along the railway in Japan. A masonry wall is one of the structures commonly used as a slope protection work in early 20th century before reinforced concrete retaining walls becoming popular. Many of the old masonry walls remain not only in the local railways but also in urban areas including the metropolitan area of Japan. In the current railway design standards, use of reinforced concrete is required for the slope protection work. The sectional view of the standard masonry wall presented by the Ministry of Railways of Japan in the past is shown in Fig. 2 (Ota, 2008). Masonry walls have been applied to both cut slopes and embankment slopes and the main purpose of their construction is to prevent erosion, weathering and collapse of the slope surface. In the case of embankment, the thicker gravel backfill has been recommended as shown in the figure. These specifications in the standard masonry wall design have been empirically determined and no design calculation has been made.

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