Structural Design of Deep Water Pontoon Mooring Anchors

Abstract

After nearly half a century of service, the world's longest floating bridge is now clogged by traffic, showing its age, and in need of replacement. The Washington State Department of Transportation (WSDOT) is building a new State Route (SR) 520 floating bridge capable of withstanding heavier windstorms, and moving significantly more people and goods.Much like a large floating marine dock, the new bridge will consist of concrete pontoons moored to 58 deep water anchors by 8 miles of steel cables. The bathymetry and subsurface conditions of Lake Washington pose unique challenges for the moorage of floating pontoons. The water depths at the anchor locations vary from 30 feet to 210 feet, and subsurface conditions range from very dense to very soft and include soils with unique engineering properties. These conditions necessitated the use of three anchor types: drilled shaft, gravity, and fluke.

A macro model for shallow foundations on granular soils describing non-linear foundation behavior

“…The new state route 520 floating bridge crossing Lake Washington (Seattle) is more than 2 km long. Bored piles, fluke anchors and gravity structures are used to anchor the mooring lines along the bridge axis, Howard, et al [11]. On the other hand, end-anchored floating bridges do not utilize anchors along the bridge axis.…”