Contractor Project

Auckland’s missing link

AUCKLAND’S $2.5 BILLION City Rail Link project passed a milestone in April, with the appointment of two construction consortia to commence the first phase of the CRL in the Downtown area.

It signalled a welcome development in what has been a shaky start to Auckland Transport’s ambitious project. But funding uncertainties mean it could be 10 years before commuters reap the benefits of the 3.6 kilometre north-south route, stretching from Britomart to Mount Eden.

For a scheme first mooted in the 1920s, CRL has been a long time coming. Yet, for the project, whose purpose it is to create a better integrated public transport system, allowing more connections between rail and bus services, it is still early days. Designed to cater for 30,000 people on the rail network at peak hours – double the number currently – while slashing travel times across the rail network, CRL aims to help free-up disjointed rail travel in New Zealand’s most populous city.

Project director Chris Meale says the joint venture appointments meant the City was now; “definitely on the way to building a key missing link in our city’s public transport network.” Britomart Station would no longer be a dead end, and journey times would be vastly reduced. Aotea would be three minutes from Britomart, Karanghape Road six minutes away and Mt Eden nine minutes.

There was wide interest from the New Zealand construction industry and beyond, Meale says, as Auckland Transport appointed Downer NZ and Soletanche Bachy JV, and ‘Connectus’, a joint venture of McConnell Dowell and Hawkins, for the first phase of design at a cost of about $3 million. CRL spokeswoman Carol Greensmith says the next phase will provide for a negotiated contract to proceed with construction.

She says Auckland Council expects the government to fund 50 percent of the cost of CRL, adding; “However, this can only be confirmed through the formal funding agreement. [Meanwhile], funding for early enabling works is from Council and [has been] approved.” Overall, the government is committed to a ‘joint business case’ with Auckland Council in 2017 and to providing its share of the funding for a construction start in 2020, meaning completion will be mid-2020s.

The government has said it is prepared to consider an earlier start to the business case provided that a number of key targets can be met. They include a demonstrable increase of 25 percent in employment figures in the city centre over current levels, (though a deadline has not officially been set) and a significant rise in rail patronage.

Greensmith says the latter target, of some 20 million trips, will be met; “well before 2020, and is on track to be reached by 2017”, laying foundations for discussions between government and the council to seal approval for the funding.

“The parties have identified the need to address funding, including how project costs are shared between government and council,” she tells Contractor.

Tunnel design

The CRL tunnels, amounting to a length of 3.6 kilometres in total, and rising a full 70 metres from Britomart to Mount Eden, will be constructed through ground that varies between rock and soft soil, and with a variation in depth to natural ground level of between 40 metres and 0 metres, at the tunnel portal. The rail tunnels between the turnout tunnels, and between the Central Motorway Junction and Mt Eden stations, and the stations at Karangahape, and Aotea will be constructed using a tunnel boring machine (TBM). Excavation is expected to generate some one million cubic meters of spoil, more even than the NZTA Waterview project nearby, since it includes large rail station excavations.

The middle section of the tunnel, between Aotea Station and the turnout tunnels near Mt Eden Stations, will be excavated in East Coast Bays Formation. These twin seven metre diameter tunnels will be driven by a TBM installed first at Mt Eden Station to drive downhill in a northerly direction first to a new station at Karangahape, then onwards to Aotea. In this section the sandstone is typically a weak rock so this tunnel section is well-suited to construction with a TBM with the turnout tunnels being constructed using mining techniques. Upon construction of the first tunnel, the TBM will be removed and reinstalled at Mt Eden for construction of the second, parallel, bore. Though driving ‘uphill’ is more typical in projects using TBM, usually as a means of simplifying ground dewatering, CRL civil design manager, Darryl Wong, says such an option is not possible in this case. That would have meant, says Wong, introducing the machine and servicing it in one of the busiest areas of the city, where mucking out and concrete segment supply would have untold disruption consequences during construction. AK-missing-link-436x300

The two ends of the tunnel (Albert Street and south of the turnout tunnels to the existing Western Line) will be constructed using cut-and-cover techniques owing to their relatively shallow depth below existing ground level. The sections of the cut-and-cover tunnels between Britomart and Aotea Stations require the section at Lower Queen Street to be constructed in stages to allow continued pedestrian flows between Customs Street West and Quay Streets.

The Zurich Building section will be constructed in bottom-up stages with access from Queen Street. The section within Queen Elizabeth II Square and within the Downtown Shopping Centre is proposed to be entrusted to Precinct Properties to construct. The crossing under Customs Street West requires staging between the north and south sides with alternate requirements for traffic management, excavation and construction of the cut-and-cover structure. Similarly, Albert Street needs to maintain traffic access. Preparation works include relocating the street furniture, adjustments to footpaths, protecting and/or relocating services, construction and excavation, and reinstatement.

Connectus, the joint venture between McConnell Dowell and Hawkins, will construct the cut-and-cover rail tunnels under and along key transport corridors in the CBD. The early contractor involvement (ECI) and design development phase commenced in March with physical work expected to start in November. The ECI contractor has begun undertaking planning and detailed design, in addition to outline and management planning for the scheme.

Connectus will be relocating an existing storm water pipe between Wellesley and Swanson Streets. The new tunnel will be delivered using specialist micro-tunnelling technology. This will involve a 500 metre long, 1950mm diameter, tunnel driven using the pipe-jacking method, with a precast concrete pipe lining. A launch shaft will be sunk at the junction of Victoria and Albert Streets and the first drive to Swanson and Albert junction will be followed by retrieval of the machine and relaunch to form a shaft at Victoria, where it will continue to the Wellesley and Albert streets junction.

CRL construction manager, Scott Elwarth, tells Contractor it is expected that the storm water tunnel construction will start in November, along with commencement of work on the cut-and-cover works. The remainder of the works are likely to begin next year.

Construction planning is one of the major challenges facing the team. The works in the area around Albert Street to the north of the project will take place alongside adjacent property developments, such as a large hotel at Victoria and Albert, explains Wong. Added to that, Precinct Properties is remodelling the Downtown Shopping Centre and building a 36-storey $500 million office tower nearby. If all goes to plan, the CRL tunnels will be built at the same time as this project.

Station construction

There are three main approaches to station construction, each of which, says Scott Elwarth, is common in underground stations around the world. A cut-and-cover ‘box’ typology will be used for Aotea Station, while a mined side-platform approach will be used for Karangahape Station and cut-and-cover ‘open’ box typology used for the new island platform at Mt Eden and Newton Stations. A common feature of all, however, will be areas satisfying associated functions such as entrances, plant room spaces, evacuation points and air vents.

Britomart Station

At a rail level some 11 metres below ground, Britomart Station is an existing facility which will be modified to accommodate the through tracks and higher capacity required for the CRL. Construction planning of the various sections of Britomart Station requires an approach that allows customers still to receive a good standard of service and the maintenance of station functionality. Temporary measures will be required as will staging between works on the Up and Down Mains to provide safe public access at all times.

A delicate underpinning operation is to be undertaken beneath what is the old Chief Post Office (CPO), requiring the closure of the facility for some three years. Details have yet to emerge, but the technique is likely to involve the installation of bored piles, typically to a depth of between 12-15m, depending on geology Darryl Wong (CRL civil design manager), explains.

“An alternative is being developed with the ECI contractor to the reference piled design solution.”

Soletanche Bachy’s expertise in this area is expected to be of particular value, as is its knowledge of diaphragm wall foundations on the project.

But, Wong points out, “There is not a lot of experience of this form of construction in Auckland.”

Aotea Station

Aotea Station could become the busiest railway station in Auckland, AT says. It will have entrances on Victoria Street and Wellesley Street, being close to Aotea Centre in the cultural precinct with the Town Hall, Civic, Q Theatre, and other attractions nearby. Construction for Aotea Station will be staged so that only one of the Victoria Street, Wellesley Street and Custom Street West access routes to the Harbour Bridge is closed at any one time. The station will be constructed top-down, inside a retaining structure consisting of piles to a depth of between 15-20 metres and shotcrete.

Works include establishing a southern construction yard and shaft, while at Wellesley Street West intersection a roof slab will be built and the Albert Street/Wellesley Street area reinstated for public use. The station ‘box’ will be constructed top-down to platform level, followed by structures for the station entrance, ventilation, and mechanical and electrical equipment.

AK-missing-link-770x311
The CRL tunnels, amounting to a length of 3.6 metres in total, and arising a full 70 metres from Britomart to Mt Eden, will be constructed through ground that varies between rock and soft soil.

Karangahape Station

At a depth of 30 metres, Karangahape Station will be the deepest station on the project. Initial works will include site preparation, utilities protection and, where necessary, diversion, and demolition of existing buildings followed by construction of the main entrance shafts, and excavation of the sloped entrances and platform tunnels. Construction of the permanent works featuring a ‘mined side platform’ method, will use roadheaders gaining access via shafts at Mercury Lane and Pitt St, and Beresford Square. These will be completed after the tunnel boring machine (TBM) has passed through the platform tunnels.

North Auckland Line Tie-In

The construction sequence of the various sections of the mined turnouts, and cut-and-cover tunnels to the NAL tie-in, includes construction of the CRL main cut-and-cover sections and excavation of the CRL main tunnels using roadheaders. The size of the excavation profile will provide the TBM with access as well as a structure gauge for the rail junction. 

The Funding Issue

One of the biggest imponderables in the roll-out of the CRL is that of funding. On June 28 2013, the Prime Minister announced the Government’s commitment to a joint business case with Auckland Council for the City Rail Link in 2017 and to providing its share of funding for a construction start in 2020. The Prime Minister also stated that the Government would consider an earlier business case and construction start date if it became clear that Auckland’s CBD employment and rail patronage hit thresholds faster than current rates of growth suggest.

The two thresholds are:

  • An increase in Auckland CBD employment of 25 percent over the February 2012 estimate (the baseline), which is half of the increase to 2021 predicted in the 2012 City Centre Future Access Study, and;
  • Rail patronage is on track to hit 20 million trips a year well before 2020.

But a Ministry of Transport statement, issued in February this year, noted Auckland Transport’s rail patronage data for the year to December 2014 shows patronage of 12,515,329 trips. This compares to 10,610,956 trips for the previous year. This is an increase of 1,904,373 trips or 17.9 percent but, the Ministry of Transport said, “We expect to see continued strong rail patronage growth until around 2017/18, as the full electric train fleet comes into service and the new bus network is rolled out. From 2017/18, we expect the rate of patronage growth to slow.

The MoT concluded: “CBD employment is currently 100,750 employees, compared to the 25 percent growth threshold of 122,528 employees.

Rail patronage for the year to December 2014 was 12,515,329 trips compared to the threshold of 20,000,000 trips well before 2020.

CBD employment levels and rail patronage are some way from reaching the thresholds set by the Government for considering an earlier business case and construction start date for the City Rail Link.”

These figures have been sourced from The 2012 City Centre Future Access Study which was commissioned by Auckland Transport following the then Minister of Transport’s call for further work to investigate options for addressing public transport access to Auckland’s city centre. This was in response to the initial business case for the City Rail Link.

The 2013 report Monitoring Employment Growth in the Auckland CBD: A Proposed Approach, by Richard Paling Consulting, considered approaches to measuring CBD employment growth and concluded that the Database provides the best source of annual employment statistics for the CBD.

Auckland Council’s response is optimistic, however. “Auckland Council’s 2015/25 Long Term Plan contains the assumption that a funding agreement will be reached with Government before the 2018/28 Long Term Plan is adopted; that this will provide certainty of government funding,” CRL’s Carol Greensmith says. “The Auditor General has confirmed the acceptability of this assumption. The targets are to support an earlier start to the business case, they are not targets to be met before the government will fund the CRL. The government has already agreed to fund the CRL from 2020.”

On the question of employment in the CBD, she adds: “A number of private sector organisations are forecasting CBD employment growth to be within the region of the government’s target. The government accepts the validity of the patronage data provided by Auckland Transport.”

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