2026 Volume 21 Issue 2 Pages 283-298
The First Sea Fortress was established in 1890 (Meiji 23) in the waters 1,200 m off Cape Futtsu in Chiba Prefecture at the mouth of Tokyo Bay to defend the capital city of Tokyo as a countermeasure to Russia’s southward policy in the middle of the Edo period. This artificial island is filled with sea sand to an altitude of 14 m, but due to the loss of sand due to rainfall and waves during typhoons, subsidence, sliding, and collapse of seawalls and batteries etc. are remarkable. The First Sea Fortress is facing a crisis of survival. This paper examines the design, construction, and engineering value of the First Sea Fortress, analyzes the current disastrous state of this structure from a geotechnical perspective, and considers future preservation strategies.
