State Route 99 Tunnel:Formwork Solution forDouble-Deck Tunnel

Quelle/credit (2): WSDOT

Inside the tunnel: within the bored tunnel tube with a diameter of around 17.50 m, a double-story road tunnel is being realized – mainly constructed using in-situ concrete together with a comprehensive Peri solution

Quelle/credit (2): WSDOT

Quelle/credit: PERI GmbH

The first working section in the tunnel tube: the realization of starter units which form the foundation for the tunnel-in-tunnel. This area is formed with custom steel formwork. The two support areas – one for the rising wall, another for the prefabricated panel which is mounted at the end of all reinforced concrete work and subsequently forms the bottom carriageway slab – are clearly visible

Quelle/credit: PERI GmbH

The rising walls are concreted directly on the starting units and in turn form the support for the upper roadway. Two Maximo formwork sets ensure fast, efficient concreting of the 4.50 m high walls

The slab is subsequently concreted by means of a total of six formwork carriages – constructed using the back-step construction method. All formwork carriages were designed with corresponding passageway openings for transporting materials in the direction of the TBM

Quelle/credit (2): PERI GmbH

The view from the north towards the completed southern tunnel entrance

Quelle/credit (2): PERI GmbH

The 1950s vintage Alaskan Way Viaduct has long been considered one of the most important thoroughfares along Seattle‘s waterfront in Washington, USA. As a replacement for the elevated viaduct that is used daily by 110 000 vehicles, a 3.2 km long tunnel is currently being constructed. Peri planned and delivered a project-specific formwork solution for the realization of the double-deck carriageway whereby the previously bored tunnel tube length is being concreted in three sections each time.

A Replacement for the Alaskan Way Viaduct

After the Alaskan Way Viaduct had suffered considerable damage due to a major earthquake in 2001, initial preparations were made for a replacement. Eight years later, plans for a bored tunnel emerged. In 2011, Seattle Tunnel Partners (STP) was awarded the contract for the design and construction of the tunnel – a joint venture of the Tutor Perini Corporation from California and Dragados USA.

Bertha, one of the world‘s largest tunnel boring machines (TBM) excavated a tunnel with a diameter of around 17.50 m was then directly lined with 60 cm thick precast...