Geotechnical interpretation of cedar piles at the Mietsu Naval Facility World Heritage Site

Abstract

The Mietsu Naval Facility (MNF) was established as a Western-style military facility by the Saga Clan in 1858. The aim of the present study was to examine the purpose and installation method of cedar logs preserved in the Small Boat Dock (SBD) section of the MNF. In order to restore the scale and shape of the superstructure at the SBD to those at the time of its construction, it was necessary to determine the role of the cedar logs. The movement of the soil particles in a laboratory model, made of Kawasaki clay and penetrated by a foundation pile, was examined in order to simulate the deformation behavior around the cedar logs. The deformation around the pile, caused by the pile penetration, increased within the range of the pile diameter. The changes in the natural water content and the undrained shear strength around several piles in the SBD were measured. The model test results revealed that the cedar logs were driven piles, and thus, not posts of the building. Based on this knowledge and additional research into architectural history, it was possible to determine the scale and shape of the superstructure, potentially leading to the restoration of the original buildings and remains.