A second immersed tube crossing of Sydney Harbour has been approved by the Government of New South Wales. The scheme has received planning permission to help reduce congestion in the Sydney central business district, cut journey times and relieve pressure on the existing bridge and immersed tube harbour crossings.

Construction of third harbour crossing is approved

Planning permission is granted despite concerns over potential damage to property and the environment caused by the landfall drill+blast excavations and marine dredging for the immersed tube. The State Department of Planning and Public Spaces concludes that these issues had been adequately addressed and that the impact of the project to the community and environment could be appropriately managed, minimised or offset to an acceptable level. The project was approved as being in the public interest.

An independent panel of geotechnical and engineering experts will be established to assess impacts of the drill+blast excavation on surface properties. The panel will review pre- and post-construction building conditions and resolve any disputes.

Damage claims were originally to be restricted to a 50m distance from excavation but will now be based on an independent geotechnical report of any buildings at risk of settlement or vibration. Vibration impacts are unavoidable for a project of this magnitude and in a highly complex and developed urban environment, planning authorities said, but that the risks are manageable and that project owner Transport for New South Wales has committed to rectifying any damage.

Separate concerns were raised about the potential impact of immersed tube dredging on the marine environment and in terms of disturbing contaminated sediment close to residential properties. In assessing these risks, the planning department noted that a backhoe dredger with closed bucket would be used to contain contaminated soft sediments and minimise suspended sediment. Also dredging would not be permitted during strong winds and silt curtains would be used to protect environmentally-sensitive areas.

The 6.5km Western Harbour Link will connect the new underground Rozelle interchange south of the harbour with the Warringah highway in the north. The estimated cost of the project is AUS$14 billion, which includes upgrading a section of the Warringah highway and connections to the proposed Beaches Link immersed tube across Middle Harbour (Fig 1). The contract for the Western Harbour connection is expected to be awarded later in 2021.

Fig 1. Underground highway development in Sydney

Three groups have been shortlisted by the New South Wales Government to tender as development partner for the new western 6.5km immersed tube highway crossing of Sydney Harbour. The shortlisted applicants are:

• Bechtel Infrastructure (Australia)
• Harbour West Partners, comprising Macquarie Capital, Jacobs and RPS
• Laing O’Rourke Australia.

Contract award is expected in 2021. The appointed development partner will assist with the procurement and delivery of the project and will be expected to leverage industry expertise, innovation and value for money to achieve the best outcomes for New South Wales.

The Western Harbour crossing will link with the underground WestConnex highway routes in the south and the proposed Beaches Link in the north. The environmental impact statement, EIS, for the Beaches Link has now been released, providing more information on the programme of work that includes 5.6km of twin three-lane underground highway, including another new immersed tube across Middle Harbour (Fig 1).

At the eastern end, the Beaches Link will include underground connections with the Western Harbour crossing and Gore Hill Freeway (Fig 2). Stub tunnels for this connection will be excavated as part of the Western Harbour programme of work. According to the EIS, the main underground routes, at up to 109m deep, will be excavated by roadheaders. The high-quality Hawkesbury Sandstone and wide cross section of the excavation makes this the most efficient and common method for constructing road tunnels in Sydney.

Opting for an immersed tube across Middle Harbour on the Beaches Link will reduce the depth and length compared to a bored TBM crossing, the EIS stated, and provide the lowest possible gradient for surface connections. The geological profile of Middle Harbour requires the immersed tube units to sit on supporting piles in soft sediments (Fig 3). Temporary cofferdams will allow construction of the interface with landside alignments.

Fig 2. Beaches Link main features

In recent years, Sydney has become a hub of roadheader activity with 50 machines currently in use excavating the 7km twin tubes of the WestConnex M4-M5 link and the Rozelle interchange complex, which comprises up to 25km of various cross section headings for traffic lanes, cross passages, ventilation and access (Table 1). They are also the proposed method of construction for the landside sections of the Western Harbour link. Previously a total of 55 roadheaders were used on the recently-opened WestConnex M4 and M5/M8 routes and on the NorthConnex highway.

Roadheaders are also proposed in the design documents for the new M6 underground highway that will link the new WestConnex M8 route south to President Avenue at Kogarah (Fig 1), although TBM excavation is also being considered and permitted in proposals from the three shortlisted contractors, Gamuda-BMD, CPB Contractors-Ghella-UGL, and Acciona-Samsung. The design-build contract for the 4km twin tubes of the AUS$2.6 billion M6 Stage 1 is now expected to be awarded in early 2021, Transport for New South Wales confirmed to TunnelTalk, slightly later than the December 2020 date previously reported.

Construction of the Beaches Link is anticipated to begin in 2023, subject to planning and procurement processes, with completion at the end of 2027 (Fig 4). “The project will transform the ways people move to and from the Northern Beaches,” said New South Wales Premier Gladys Berejiklian. “Bypassing 19 sets of traffic lights, the route will help save 56 minutes when travelling between Dee Why and Sydney Airport.”

Fig 1. New Western Harbour and Beaches Link western bypass route

A second highway crossing of Sydney Harbour, to the west of the famous bridge and its existing capacity adding immersed tube crossing, is presented to the industry for expressions for a potential development partner to assist with procurement and delivery. The crossing is part of the wider Northern Beaches extension which is proposed to be a new tunnel from the northern beaches of Sydney, under Middle Harbour and connecting to Gore Hill Freeway and the Warringah Freeway (Fig 1). Transport for NSW expects to have more details on the Beaches Link project later in 2020 as part of the project’s environmental impact statement.

Unlike other highway projects in Sydney that have or are being delivered by a toll road operator, the Western Harbour crossing and its Northern Beaches Link are New South Wales State Government led projects. After engagement with industry, the NSW Government decided on a State-led procurement and delivery process and announced that through the expressions of interest, “we will be seeking to leverage private sector expertise such as innovative ideas and approaches to procurement and delivery”.

The Western Harbour link is proposed by NSW Transport in its reference design as an immersed tube crossing with mined tunnels at the landfalls (Fig 2). To the south, the underground harbour crossing will link to the underground Rozelle interchange and WestConnex highway routes and M6 underground Stage 1 alignment. To the north there will be a connection to the North Beaches extension and its tunnel crossing of Middle Harbour and also to an upgrade of the Warringah Freeway that links to the Harbour Bridge and Tunnel crossing (Fig 3).

The Warringah Freeway is one of the busiest roads of the city and its upgrade is designed by NSW Transport to increase safety for motorists and deliver better active transport links along the 4km upgrade stretch, and provide seamless connections to the Western Harbour Tunnel and Beaches Link. Procurement of the 4km Warringah Freeway upgrade is a separate call for expressions of interest process with NSW Transport.

The current call for expressions of interest for the Western Harbour project stated that “the potential involvement of a development partner will focus on procurement and delivery structures and not the financing of the project. Project costs will be finalised when construction contracts have been awarded.”

Warringah Freeway leading from north to the Harbour Bridge and Tunnel crossing, one of the busiest traffic routes in Sydney

Vertical alignments of existing and planned highway tunnels in Sydney

In creating a western bypass of the Sydney city centre, the Western Harbour Tunnel is designated as a nationally significant project to transform the way motorists move around the city and deliver faster and more reliable journeys under the harbour. NSW Transport in an email stated that: “In presenting their delivery partner proposals, tenderers will be able to propose their preferred tunnelling approach, ensuring the work delivers benefits including value for money and programme, performance and environmental outcomes – in construction and operation.”

Preliminary planning for a western crossing of Sydney Harbour began in 2015 with an initial design completed in March 2017 and the application for status of State Significant Infrastructure submitted in November 2017. Community engagement progressed from July to December 2018 and the project is currently completing its environmental impact assessments ahead of seeking planning approval. An indicative construction timeline of about six years, starting in 2021, has a potential opening date in 2026 or 2027.

Ahead of that, Sydney is:

• Preparing to open its NorthConnex underground highway;
• Has opened two parts of the underground WestConnex highway – the M4 and M5/M8 sections, and is progressing the WestConnex M4-M5 underground link and underground Rozelle interchange;
• Is evaluating proposals for the M6 Stage 1 underground highway project for award of a contract in early 2021 where TBMs may be the excavation method selected as opposed to the preference to date for roadheader excavation; and
• Is moving ahead with the Beaches Link highway with its underground crossing of Middle Harbour.

These projects add to existing underground roadways in Sydney including the existing Harbour immersed tube crossing, the Lane Cove project completed in the early 2000s and the Eastern Distributor double deck highway completed in the late 1990s.

They also add to the many kilometres of underground metro and rail projects completed in recent years and the many currently in planning.