William Street tunnel

The William Street tunnel is a railway tunnel under the central business district of Perth, Western Australia. Built between 2004 and 2007 as part of the construction of the Mandurah line, the tunnel connects it to the Yanchep line, running under William Street for much of its length. It consists of of twin bored tunnels, a cut-and-cover tunnel at either end, and two stations: Perth Underground and Elizabeth Quay.
The Mandurah line was initially proposed to branch off the Armadale line. After a more direct route was chosen in 2001, a tunnel under the central business district became necessary to connect the Mandurah line to the rest of the network. The construction of the Mandurah line was divided into eight contract packages; the William Street tunnel was part of Package F, also known as the City Project, the contract for which was awarded to Leighton–Kumagai Gumi in February 2004 for $324.5million. Preliminary works began the same month, and tunnelling began in October 2005, starting from Elizabeth Quay station and heading north. Boring for the first tunnel was completed in June 2006, after which the tunnel boring machine was transported back to Elizabeth Quay to dig the second, which was completed in October 2006.
Construction was disrupted by industrial action, which culminated in the prosecution of 107 workers for illegally striking in February and March 2006 following the issuance of a strike ban by the Australian Industrial Relations Commission. The strikes, along with complications involving heritage protection at Perth Underground station, engineering challenges on the Swan River foreshore, and contract disputes, resulted in the tunnel's opening being delayed beyond the 2006 deadline. The first train entered the tunnel in August 2007 and it opened to passengers on 15 October, ahead of the rest of the Mandurah line's opening on 23 December. The final cost, after contract disputes were settled, was $439.3million.

Description

The William Street tunnel consists of approximately of twin bored tunnels, plus adjacent cut-and-cover tunnels. The tunnel has two stations: Perth Underground, which was known during construction as William Street station, and Elizabeth Quay station, which was known before 2016 as Esplanade station. Trains in the William Street tunnel are part of both the Mandurah and Yanchep lines between Perth Underground and Elizabeth Quay stations. North of Perth Underground is the Yanchep line and south of Elizabeth Quay station is the Mandurah line. The bored tunnels have an internal diameter of, with lining. The rails range from below ground level. The tunnel has a design life of 120 years.
The southern cut-and-cover portion, a distance of approximately, commences east of the Mitchell Freeway along the Swan River foreshore, and ends at the intersection of Mounts Bay Road and William Street, where Elizabeth Quay station is. North of the station, the tunnel runs under William Street as two bored tunnels, one for each track. The tunnel veers east of William Street to reach Perth Underground station, which was dug cut-and-cover. The bored tunnels then bend west to enter the rail corridor west of Perth station, which is the former Perth marshalling yard. The tunnel then has a ramp structure taking it up to the surface to connect with the rest of the rail network. This was originally not part of the tunnel, but the ramp was covered as part of the Perth City Link in the 2010s. The minimum curve radius for the tunnel is due to geometric constraints, far below the minimum curve radius of used elsewhere on the Mandurah line.

Planning

Initial plans for the Mandurah line, created by a Liberal state government, had it branch off the Armadale line at Kenwick, which did not require a tunnel through Perth's central business district. Experts, including Murdoch University professor Peter Newman, called for a direct route to be constructed instead, which would have necessitated a tunnel through the CBD. The Labor Party nonetheless supported the Kenwick route in the lead up to the 2001 state election. After Labor's election victory though, the new Cabinet of Western Australia decided in July 2001 that the direct route would be constructed instead of the Kenwick route. To connect the line to the rest of the rail network, the new route required a tunnel under the central business district, which was to be a cut-and-cover tunnel along William Street. There was to be an elevated portion south of St Georges Terrace too, which was strongly criticised by the lord mayor of Perth, Peter Nattrass, who said the elevated section along the Swan River foreshore would be an "eyesore" like the Cahill Expressway in Sydney. The minister for planning and infrastructure, Alannah MacTiernan, tried to allay his fears by leaving open the possibility that the tunnelled section would extend further south than St Georges Terrace.
In response to criticism of the Mandurah line's route through the Perth CBD, the Perth City Rail Advisory Committee was formed in October 2001 to assess other options. The committee consisted of eight members, including engineers, planners, and representatives from the Property Council and the Perth City Council, and was tasked with submitting its report in February 2002. The report was delayed as the committee struggled to reach a consensus; it was released on 14 March 2002. It assessed sixteen options, of which three were shortlisted:

The western route runs along the Mitchell Freeway, entering a tunnel south of Malcolm Street to exit the freeway median strip, before bending east to surface in the existing rail corridor, terminating at Perth station from the west. There would be an underground station at Elder Street between Hay and Murray streets, near Parliament House. The estimated cost of the western route was $140.1million. This option required reversing trains at Perth station to retain through-running with the Joondalup line, necessitating an additional train for $18million. This was the committee's second-most preferred route.
The central route runs in a cut-and-cover tunnel along William Street, bending west to connect with the Joondalup line. There would be underground stations at William Street near the Esplanade Busport and at William Street between Murray and Wellington streets, with a walking connection to the existing Perth station. This route differs from the government's proposed route planned by the Perth Urban Rail Development office by having the line underground south of The Esplanade instead of elevated. The estimated cost of this option was $139million. This was the committee's least preferred route, because of the significant disruption caused by the cut-and-cover construction.
The eastern route runs in a bored tunnel parallel to Mounts Bay Road and The Esplanade, before bending north to run along Irwin Street, then bending west to reach Perth station. There would be underground stations at the Esplanade Busport and Irwin Street near Hay Street. The estimated cost of this option was $311million. This was the committee's preferred route. Another route considered involved tunnelling under St Georges Terrace instead of along Mounts Bay Road and The Esplanade; this was ruled out for its high cost, risks, and disruption to St Georges Terrace to construct a station there.

The City of Perth commissioned Halliburton to write its own report, which was released days before the committee's report and favoured the western route. The state government ruled out the eastern route as it would cost more than twice the other routes. The remaining two routes were opened up to public consultation over the following month. The western route was the Perth City Council's preferred route, due to its limited impact on businesses. However, that route would cause significant disruption to the Mitchell Freeway during construction and integrate poorly with the surrounding area. The Perth Convention and Exhibition Centre also preferred the western route, as it claimed a station at the Esplanade would be a security risk for the convention centre if it were to host heads of state. In April 2002, the Perth City Rail Advisory Committee was re-established to conduct a more detailed analysis on the two remaining routes, with the central route to be considered as a bored tunnel rather than cut-and-cover. An opinion poll by The West Australian newspaper found that 39 per cent of respondents supported the central route and 35 per cent of respondents supported the western route. The Perth City Rail Advisory Committee completed its second report in May 2002, which recommended the central route. State Cabinet endorsed this route in June, with Lord Mayor Peter Nattrass now being in support of the improved central route. A master plan for the Mandurah line's direct route was released in August 2002.

Procurement

The construction of the tunnel was known as the City Project, which was designed and constructed as part of Package F of the Southern Suburbs Railway. Construction was managed by New MetroRail, a division of the Public Transport Authority. Geotechnical testing by Golder Associates occurred between January and March 2003. Expressions of interest for Package F were called for in March 2003 and closed in April 2003. Five consortia submitted expressions of interest for the contract, which was valued at $200million.
A design change was announced in July 2003: the William Street bridge on the foreshore was now to be demolished. The $1.3million cost was to be offset by changes to the project's design, including leaving a section of the tunnel uncovered within the freeway interchange and using natural light and ventilation for Esplanade station. Concerns were raised regarding an increase in traffic congestion caused by the removal of the bridge, but Lord Mayor Nattrass supported the removal of the bridge because it allowed for a future redevelopment of the foreshore. After lobbying from the Perth City Council, consideration was given to sinking the Fremantle line within Northbridge as part of the William Street tunnel's construction. The state government attempted to reach an agreement for the City of Perth to fund the sinking in exchange for the city receiving the right to develop the land on top of the railway, but with an estimated cost of $200million, it was deemed too expensive. This section of railway was later sunk for $360million as part of the Perth City Link project in 2012 and 2013, the new tunnel passing just above the William Street tunnel. In conjunction with this, the roof of the William Street tunnel was extended from Lake Street to Milligan Street, enabling development above the tunnel.
Of the five consortia, CityConnect and Leighton–Kumagai Gumi were shortlisted in May 2003, and in November 2003, Leighton–Kumagai Gumi was selected as the preferred proponent. The managing director of Clough did not want to agree to the government's requirement that the contractor take all the risk for cost escalation due to unknowns such as soil conditions and heritage buildings. The following month, the contract was approved by Cabinet, with the cost rising to about $320million, making the cost of the Southern Suburbs Railway $1.059billion. The cost increase prompted shadow transport minister Katie Hodson-Thomas to call for the project to be "reconsidered" and National Party leader Max Trenorden to call for MacTiernan to be stood aside pending a parliamentary review into the project. In February 2004, the contract was signed for $324.5million.
As a result of pressure from the Liberal Party and Greens, MacTiernan promised in January 2004 to table the contract in Parliament, although Leighton opposed this. The contract was controversial due to the previous cost blowout and the risks of tunnelling. MacTiernan promised that almost all the risk would be on the contractor as it was a fixed-price contract, with the state liable for underground building anchors and the relocation of power and water utilities. The contract was tabled on 2 March 2004. MacTiernan claimed it was the first time a contract for such a construction project had been publicly released. The contract stated that delays beyond October 2006 would incur a penalty of $54,000 per day for the contractor. Throughout construction, MacTiernan emphasised that it was a fixed-price contract in response to speculation about cost blowouts. In August 2005, the state's auditor general released a report that said the City Project's contract management had been good, but that further cost escalations were possible.