HISTORY OF ROCK EXCAVATION FOR BRIDGE FOUNDATION USING LARGE SCALE GRAB DREDGER

For the foundation of the large bridges connecting Honshu and Shikoku, excavation for the 2P and 3P piers of the Akashi Kaikyo Bridge, following similar work on the Seto Ohashi Bridge, were carried out using a large scale grab dredger. High accuracy was achieved, leading to success of the laying down caisson method.Large scale grab dredger have demonstrated their ability to dredge conventional navigation channels, particularly in excavating bedrock for the navigation channel through the Kanmon Strait. Consequently, the method was adopted for the underwater bedrock excavation of bridge piers for the Kurono Seto Bridge, the Seto Ohashi Bridge and the Akashi Kaikyo Bridge.This report describes the transition of grab dredger and the bedrock excavation of bridge foundations.