Abstract
In this study, the deformation and displacement of stone walls in Kumamoto castle before and after 2016 Kumamoto Earthquake were investigated. In this paper, two stone-walls (Uto- and Hira-yagura turrets) were focused. The 3-D geometry obtained by 3-D laser scanner was compared with the previous measurement by Kuwabara (1984) (a certain traverse line) to investigate the deformation and displacement of stones caused by the earthquake. The 3-D point clouds obtained in different days after the earthquake were also compared to investigate the progressive deformation/displacement of geometry caused by aftershocks and torrential rainfalls after the earthquake. The results obtained from deformation analyses clearly shows that the progressive deformation/displacement can be observed on the north stone wall of Hira-yagura turret and this progressive displacement (about a few cm) was continued until May 2017 after 2016 Kumamoto Earthquake. On the other hand, the significant deformation/displacement of stone walls of Uto-yagura turret cannot be observed clearly. In conclusion, the necessity of measurement by 3-D laser scanner and data storage of point clouds data for the maintenance of masonry structures.
The stone walls in Kumamoto castle were seriously damaged by Kumamoto earthquake that occurred on the 14th and 16th of April, 2016. The magnitude of the foreshock (14th of April) and main shock (16th of April) were 6.5 and 7.3, respectively. According to the report of investigation after earthquake, more than 30% and 10% of the stone walls in Kumamoto Castle were deformed (including loosening, masonry joint opening, bulging, flaking etc.) and collapsed, respectively. At present, emergency countermeasures such as shotcrete and falling stone protection nets have been taken to prevent further collapse and deformation caused by aftershocks and rainfalls. However, it is necessary and important to evaluate the stability of stone walls to investigate the possible restoration and reinforcement of stone walls which avoided collapse but suffered damage by earthquakes. Also, it is important to consider the traditional construction methodology (dry masonry) from historical point of view. Therefore, modern technology for restoration and reinforcement cannot be applied easily.
