Over the weekend an article titled Tunnel under city or face rail chaos appeared in Melbourne newspaper The Age, with the lead image being a pretty artists impression of a new underground railway station beneath Flinders Street Station.
The article had the following to say:
State government documents obtained by The Sunday Age reveal that unless work begins soon on the so-called ”Melbourne Metro” rail project, several of the city’s busiest train lines will come under further strain because the number of passengers will outstrip services.
The long-awaited Melbourne Metro project involves building a nine-kilometre tunnel across the inner city, with five new underground stations between South Kensington and South Yarra: Arden, Parkville, CBD North, CBD South and Domain.
The tunnel will in turn link the Sunbury rail line, in Melbourne’s north-west, to the Dandenong rail corridor in the outer south-east, allowing an extra 24,000 passengers an hour across the train network.
So when did the government come up with the tunnel idea, and on what route are they planning to build it?
Proposals for the tunnel first became public in 2008, when it was featured in the ‘East West Link Needs Assessment Study‘ produced by Sir Rod Eddington. This version of the tunnel was 17 kilometres long and was to be built in two stages:
The stage one route would start west of the existing West Footscray Station, with the tunnel running generally under the Maribyrnong River, under Kensington adjacent to J.J. Holland Park, under the North Melbourne Cricket Ground and the Royal Children’s Hospital to the Parkville precinct. To complete stage one, the route would head south under Swanston Street and St Kilda Road to the Domain.
Stage two tunnelling would run from Domain to Caulfield to cater for growth on the Pakenham, Cranbourne and Frankston lines (the Caulfield Rail Group) and would follow an alignment down St Kilda Road and Dandenong Road. Opportunities could be explored for stage two to involve cut-and-cover tunnelling along St Kilda Road and Dandenong Road to reduce the cost of tunnelling and station construction.
With the Victorian Government having no funding available from their own pocket or that of the Federal Government to build the complete tunnel project, in 2011 they they went back to Infrastructure Australia with a revised plan that reduced the overall costs:
Melbourne Metro is a proposed nine kilometre rail tunnel between South Kensington in the west and South Yarra in the south-east, connecting the Sunshine and Dandenong rail corridors via Melbourne CBD, but bypassing the congested inner core rail network. The current proposal is designed to deliver the benefits of 17 additional city-bound train services per hour in peak periods.
The project is forecast to provide additional capacity for 24,000 passengers per hour initially, rising to 60,000 per hour when other capacity constraints of the network are removed. It is expected that 140,000 passengers will use the Melbourne Metro during the morning peak by 2030.
If you look on the Public Transport Victoria website for a route map, all you get is this pretty red line squiggled over inner city Melbourne.
The also have eight artists impressions in an online photo gallery but they fail to give you any detail as to which station they are! For that reason, I’ve gone through all of the the publicly available Melbourne Metro images I could find, made some educated guesses, and annotated them to the best of my knowledge.
We start at Arden station in North Melbourne, looking north-west at the corner of Laurens Street and a new east-west street.
When you take a closer look there is only one station entrance structure shown: given that this station is situated away from existing high-density development, the level of patronage here will be the least of the five Melbourne Metro stations.
Next up is Parkville station at the corner of Royal Parade and Grattan Streets: the Royal Melbourne Hospital to the left, and the University of Melbourne to the right.
When we take a close look here we see three station entrances: one on each side of Royal Parade to serve university and hospital patrons, and a third escalator emerging at the centre of the road tram super stop for those changing transport modes.
The cutaway view of Parkville station shows how deep it will be below the ground: traversing two flights of escalators will be required to travel from concourse level down to the platforms.
Next up is CBD North, which will act as an interchange station with the City Loop at Melbourne Central Station. The artist’s impression looks south along the station concourse below Swanston Street at Lonsdale Street: the wooden ‘box’ at Melbourne Central is visible above the skylights, with the Unilodge on Swanston apartment tower in the background. I was unable to find any more detail about the station – the skylights might emerge on Swanston Street somehow, but where will the linkage to Melbourne Central be provided?
CBD South is next, and will serve as the interchange with Flinders Street Station. The north end of the station will be located at the corner of Swanston and Collins Street, where an incredibly deep hole in the City Square will lead down to the platforms themselves.
An artists impression from the opposite direction shows how escalators will reach the concourse from Collins Street outside Town Hall.
We now return to the artists impression from The Age, which shows the southern end of CBD South station. Here multiple concourse levels are linked by escalators, and an underground link from the station leads into the bottom level of the Federation Square visitors information centre.
Finding how the CBD South station would hook into Flinders Street Station was a bit trickier, but the design brief for the 2012 Flinders Street Station Design Competition came up with the goods. As well as the previously mentioned linkage to Federation Square, we also find a walkway leading west from Swanston Street beneath the Flinders Street roadway, where it turns south to the station building itself.
A profile view of the walkway is also found in the design brief, showing that the escalators will emerge onto the main station concourse near those from platform 1. With four escalators provided, the document estimates that by 2046 around 20,000 patrons will transfer between the two stations during the two hour morning peak period each weekday.
The final Melbourne Metro station is Domain, located on the corner of St Kilda and Domain Roads.
Three exits will be provided, in a similar way to Parkville station: one entrance either side of St Kilda Road, and a third one emerging at a tram super stop.
The Yarra River
The one thing I haven’t mentioned so far – how are they going to get the a new east-west tunnel under the Yarra River, while also avoiding the four existing City Loop rail tunnels near Melbourne Central, and the two CityLink road tunnels at Southbank. The answer is found in the 2008 East-West Link Needs Assessment ‘Analysis on Rail Capacity’, which provides this very useful diagram showing the vertical alignments that are available for the tunnel.
Deciding to tunnel beneath existing roads and at a great depth, the report has the following to say about the geotechnical issues faced:
The vertical and horizontal tunnel alignment that is likely to present the most favourable tunnelling conditions through the CBD is a deep tunnel aligned beneath St. Kilda Road, Swanston St and passing up to University Square, and vertically aligned such that the tunnel is formed completely within the rock of the Melbourne Formation.
Tunnelling within existing road envelopes avoids the conflict with the foundations and basements associated with existing structures. The factors that will influence the minimum tunnel depth along this alignment will be the depth of the Yarra Delta sediments, the existing Melbourne Rail Loop Tunnels, the CityLink Tunnels and the existing foundations and sub-surface structures.
It is expected that to pass beneath the Yarra River, and stay within the Melbourne Formation, the tunnel will have to be in the order of -42mAHD deep. At the intersection of Grant Street and St Kilda Road a tunnel depth of approximately -20mAHD is likely required to pass beneath the CityLink Tunnels, and at Lonsdale Street a depth of approximately -15mAHD is likely required to pass beneath the existing rail loop tunnels.
For those who can’t read surveyor language, a depth of -15mAHD at the City Loop translates to 35 metres below Melbourne Central Station, and -42mAHD at the River Yarra translates to 42 metres below sea level, or 52 metres below Flinders Street Station!
The report goes on to state the disadvantages of the deep level construction:
The main disadvantage of a deep tunnel will be the increased costs associated with the construction of stations at a greater depth, the higher running costs associated with trains operating on tracks at the limiting vertical geometry and stations at the low points, and longer passenger access travel distances.
It also considered a shallower route below the Yarra River, which is considerable riskier from a tunnelling perspective:
The main advantage of the shallower tunnelling option is the easier access that would be provided for passengers and reduced cost associated with the construction of the stations at shallower depth. However, this saving may be offset by the increased tunnelling costs associated with the above risks.
One only needs to look at the issues Transurban continues to face with the Burnley Tunnel to see how tunnelling through undesirable ground conditions can drive up maintenance costs.
A second report from the 2008 East West Needs Study also goes into detail regarding tunnelling – the Engineering Design and Costing Report by SKM, Maunsell, and Evans and Peck. For the section between Carlton and North Melbourne they have the following to say:
A section of the new tunnel will pass under existing properties between Carlton and North Melbourne. This 2.5km connection is required for the tunnel alignment to meet the project objectives as there is no vacant land available in this area and no direct route beneath an existing road reserve. As this section of the tunnel is proposed to be approximately 50m below ground level, it is anticipated there will be little or no impact at surface level.
So how does a station 50 metres below ground compare to the rest of the City Loop? Quite a bit deeper – Wikipedia says Melbourne Central is 29 metres deep and Flagstaff is 32 metres down, while the company that helped build the loop says the lower platforms at Parliament are 37 metres below ground.
If you think heading 50 metres below ground to catch a train is an escalator too far, you’d better not visit Pyongyang, St Petersburg or Kiev: they all have metro stations more than 100 metres below the ground!
- Tunnel under city or face rail chaos: The Age, December 2, 2012
- Melbourne Metro rail tunnel construction to wreak havoc on Swanston St for a year: Herald Sun, November 10, 2012
- Cash may protect corridor as rail tunnel plan digs deep: Herald Sun, May 04, 2012
- Metro a hub of underground activity: Herald Sun, October 28, 2010
- Designs revealed for new Melbourne Metro station: Architecture and Design, September 9, 2009
- Gallery of artists impressions from the PTV Website
- Analysis on Rail Capacity reportfrom the 2008 East-West Link Needs Assessment Study