Deep foundation for offshore pier of Hakucho Oohashi Bridge

The Hakucho Oohashi Bridge in Muroran City, Hokkaido is a suspension bridge with a central span of 720 m and side spans of 330 m for a total length of 1380 m. As a vital link in the municipal traffic loop line it is helping to revitalize urban functions in Muroran City, creating a wide-area traffic network with a direct link to the trans-Hokkaido highway system. The Hakucho Bridge is the first long-span suspension bridge built in Japan’s snow region and is characterized by the depth of its pier foundations. Under one main tower foundation in particular the support layer is 73 m below sea level. A diaphragm wall was built to hold back soil and water, and the area inside was then excavated to build the foundation. This paper discusses the construction of the continuous underground wall (106m excavation depth) and the method of excavating to 73 m inside this wall to build the main tower foundation.