There are a lot of historic castle masonry walls all over Japan. Those are regarded as the important cultural properties to be conserved. However, in recent years, the masonry walls frequently suffered the collapse due to the strong earthquake such as the 2016 Kumamoto Earthquake, and the investigations on the mechanical characteristics and the effective reinforcement method of the masonry walls have become the urgent task. In this study, to study the influence of the vertical excitation on the stability of the masonry wall, a series of shaking analysis was carried out using the coupled Numerical Manifold Method and Discontinuous Deformation Analysis (NMM-DDA), a discontinuum-based numerical method. The simulated results showed that the vertical excitation changes the apparent gravity of the soil and the stones, and consequently affect the amount of the deformation during the excitation.

1 Introduction

There exists a lot of castle masonry walls all over Japan, and the conservation of them become the important task because they have aesthetic landscape and sophisticated construction techniques. However, in recent years, the masonry walls frequently suffered the collapse due to the strong earthquakes such as the 2011 Great East Japan Earthquake and the 2016 Kumamoto Earthquake (see, Fig. 1). After these earthquakes, the investigations on the reinforcement method have become the urgent task for the conservation of their historical values and the prevention of the human damages. To propose a proper measure, the mechanical characteristics of the masonry walls during the earthquakes should be revealed.

In order to understand the behaviors of the masonry walls, the mechanical interaction among the stones and the backfill soil should be considered. Since the masonry walls sustain the backfill soil by the friction between the stones, the characteristics of the friction and the earth pressure during the earthquake is a key factor to evaluate the stability of the masonry walls. Moreover, the previous studies pointed out that the vertical excitation may induce the changes in contact conditions and friction strength among the stones, and the phase difference between horizontal and vertical waves also influences the stability of the masonry wall (Ikemoto et al. 1995, Koyama et al. 2016). In this study, therefore, a series of shaking analyses of a masonry wall with vertical excitation is conducted.

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