The Sydney Metro Northwest Skytrain project

Formally known as the Sydney Metro Northwest SVC Contract, the viaduct and curved cable-stayed bridge was at the time of construction the centrepiece of Sydney Metro Northwest, the first phase of Sydney Metro, the country’s biggest public transport project to expand the city’s links with its surrounding precincts.

The bridge was described as the most visibly striking part of the project in Sydney since the Harbour Bridge nearly a century ago. Along with the viaduct, it would go on to win a series of awards for its elegance and sustainability, as well as the innovative construction techniques to overcome design and construction challenges. Webuild’s attention to quality, safety, the cultural diversity of its workforce, and the benefits that the project was to bring to the community was also commended.

The SVC in the formal name of the project means surface and viaduct civil works. The were designed by SMEC and built by Webuild under its previous name, Salini Impregilo, for Transport for NSW, the government agency overseeing the development of public transport in the state of New South Wales.

Sydney Metro Northwest runs for a total of 36 kilometres, with 13 metro station and 4,000 commuter car spaces. It brings public transport services to an area where its population is forecast to increase by 200,000 in the coming decades, reaching more than 600,000, or twice that of Canberra, the country’s capital.

The Benefits of the Project

Since it went into service, the rail line of which the viaduct and bridge are a part has provided a major relief for commuters by eliminating tens of thousands of car trips per day.

As Sydney’s first fully automated train system, the line runs peak services every four minutes, enabling it to move more people, more often, and cater to the demands of the city’s growing population.

The Sydney Metro Northwest Skytrain Project Details

The four-kilometre viaduct and the 270-metre curved cable-stayed bridge run between the suburbs of Bella Vista and Rouse Hill in the city’s northwest. The viaduct stretches between Balmoral Road and Windsor Road. The bridge is located in Rouse Hill. There are also two elevated stations. 

The bridge has two towers, reaching 45 metres in height. Each tower has 16 pipes containing scores of cables that fix them to the deck in order to lend support. The bridge deck is made up of 88 concrete segments, each weighing between 70 and 140 tonnes. 

Webuild was also able to reduce the impact that its work had on the surrounding communities. It left seven major roads and a bus lane open during construction. One was the Windsor Road in Rouse Hill where 50,000 vehicles passed every day.

The workforce of more than 4,000 was international, with people hailing from 50 countries. Despite their disparate backgrounds, they were able to keep the lost-time injury rate at a tiny 0.1 – highlighting the importance that was given to safety.

Sydney Metro Northwest Skytrain Project: Innovation and Technologies 

One of the greatest challenges was adapting the design to construction requirements. In particular: overcoming significant torsional effects due to the curvature of the deck, in the presence of railway and stay loads. 

One of the most innovative features of the project’s construction was the use of a unique set of giant, mobile horizontal cranes, or launching gantries, to build the skytrain bridge and deck of the viaduct. They sat atop the piers, or columns, of the future structure in order to lift the precast concrete segments, or girders, into place. Although Webuild, previously known as Salini Impregilo, had used this system for the construction of the elevated part of a highway in Dubai, it had to modify it radically for the project. Each gantry was 150 metres long and weighed 600 tonnes.

Salini Impregilo used the gantries to build the deck of the bridge because it was much faster than conventional methods like scaffolding or falsework that would have involved ground machinery and a crane to put the girders into place. With each gantry hoisting 20 girders at a time, its workers were able to erect a span more than twice as fast as usual. Each span comprised 10 girders, so they worked at a pace of up to two spans a week.

A concrete plant to produce the girders was set up close to the site so workers could exert complete control over the process. This was necessary because each girder was unique and had to be carefully cast to fit with the others along a given span. The girders for the bridge were particularly challenging due to their curved shape of the bridge. There were 88 of them to be made, each weighing between 70 and 140 tonnes. As for the concrete mix, additional ingredients like slag and fly ash were chosen to reduce the level of CO2 that the production of the girders emitted at the facility.

Webuild Awards

The project was awarded the best rating by the Infrastructure Sustainability Council of Australia (ISCA), joining the World-Class Best Practice in Sustainability. In particular, it received two awards, both for design – Leading IS Design rating – in 2015, and for building – Leading As Built IS rating – in 2017.

It also earned 2018 Project of the Year and 2018 Global Best Projects for the railway sector from Engineering News-Record (ENR), the influential U.S. trade magazine.

Other acknowledgements included an award of excellence in infrastructure from the New South Wales branch of the Concrete Institute of Australia.