In recent years the Melbourne Metro rail tunnel has been an on and off again project, which to the public has just been a line drawn north-south over a map of the Melbourne CBD. I pieced together whatever plans I could find a few years ago, but the recent publication of the Melbourne Metro business case dated December 2011 was a big win – it features the gory technical details I have been hanging out for. So let’s take a look!

Some background

My initial blog post covers the origins of the Melbourne Metro concept – a short summary:

2008: ‘East West Link Needs Assessment Study‘ produced by Sir Rod Eddington features a 17 kilometre long tunnel, to be built in two stages under Swanston Street.

September 2009: Release of design concepts for the new underground stations.

2011: Victorian Government goes to Infrastructure Australia for help funding a shorter 9 kilometre tunnel, to be built in single stage and terminating at South Yarra instead of Caulfield.

2012: Visitors on my blog speculate regarding the depth of the tunnel – will it be deep under the existing City Loop tunnels as per early plans, or cut and cover down Swanston Street?

May 2014: Liberal Government under Premier Denis Napthine proposes an alternate Melbourne Rail Link plan.

April 2015: Labour Government under Premier Daniel Andrews announces Melbourne Metro is again the preferred project, via a shallow tunnel under Swanston Street.

And finally, here we are in May 2015 with the Heral Sun uploading a copy of a planning document dated December 2011 – you can download the full document here.

Planning stages

Inside the business case the reasoning behind how the chosen alignment was decided upon is given, as well as the alternate routes that were rejected.

Figure 4-1 shows the rail corridor options initially considered back in 2007-2008, which resulted in a north-south tunnel being preferred.

With a route decided upon, station locations and the alignment of the tunnel had to be decided upon.

Figure 4-3 shows the station and alignment options considered.

The options were presented in a schematic form in figure 4-4.

Options for the alignment between Domain station and Caulfield also had to be considered – figure 4-5 shows these.

A result of the above work, in 2011 the decision was to build the Melbourne Metro as a single stage, with two CBD stations, a rail tunnel beneath Swanston Street, and a southern connection to the rest of the network at South Yarra station. The business case had this to say about this choice:

Preliminary assessments of Russell Street and Elizabeth Street alignments indicated that they would be $430 million and $600 million more expensive than the default, respectively. Investigation of a western CBD alignment via William Street was pursued at the request of City of Melbourne. A William Street alignment through the CBD would also cost an additional $470 million. A single CBD station would provide a considerably poorer outcome in terms of interchange with the existing rail network, access to employment and other activities and relief to the tram network. It would result in 15% fewer passengers using MM compared to the default arrangement of two CBD stations. Recent investigations have confirmed Toorak Road as a feasible alternative to the default scheme which provides similar benefits earlier and [snip] and significant short-medium term cost savings of $2.5 billion compared to the full default scheme.

Another decision to be made was the vertical alignment. Back in 2008 the East-West Link Needs Assessment ‘Analysis on Rail Capacity’ document featured two deep tunnel options, both of which passed below the existing City Loop and CityLink tunnels.

The 2011 business case had this to say on the alignment options:

The initial concept that underpinned the 2010 business case adopted a vertical alignment of the tunnels in Swanston Street which passed underneath the existing Melbourne Underground Rail Loop (MURL) tunnels east of Melbourne Central. This resulted in relatively deep and expensive station boxes, with CBD North being 43m deep at track level. This option included a maximum grade of 3.5%. Following the peer review, further detailed work was undertaken during 2011 to assess constructability and feasibility of a shallower tunnel and stations along Swanston Street and to refine the alignment and station configurations. A shallower (higher) alignment would result in a better outcome for passengers and may provide cost savings. The constructability assessment showed that a high alignment was feasible, though the tunnels would be more expensive to build and disruption would be more significant. The Yarra River crossing would also present greater challenges and risks. Significant cost savings would be expected in construction of the stations however.

A comparison of the high and low level alignment is shown diagrammatically in Figure 4-11.

A comparison of the station depths was also included in Table 4-9.

The business case went into the benefits of the shallower tunnel for passengers:

The improved access associated with the high alignment and shallower stations reduces passenger walking time to surface at CBD North Station by around 90 seconds and CBD South Station by around 60 seconds.

It also went into how a shallow crossing of the Yarra River would be built:

The Yarra crossing is proposed as an immersed tube construction due to the shallow depth of the alignment. This method requires dredging of the river bed prior to floating into the place the prefabricate tube sections. It is proposed to construct the tube sections on the south bank of the river on east of the existing boat sheds.

Stations

Once the stations locations were settled, the entrances to said stations also had to be decided upon.

Each of two CBD stations have been provided with two concourses (at the north and south ends of the station) while the other stations have been only provided with one (in the centre of the station).

Arden

From the 2011 business case:

Nine potential station entrances were examined. One station entrance was assessed as sufficient.

And a matching render from the PTV website circa-2012:

Parkville

From the 2011 business case:

Nineteen potential station entrance locations were proposed for the Parkville station. Two main entrances on the east and west side of Royal Parade were identified as important. In addition, three special entrances were considered, notably the train-to-tram interchange in Royal Parade and direct concourse access to the Victorian Comprehensive Cancer Centre (VCCC) and the Peter Doherty Buildings.

A matching artists impression from 2012:

And an earlier design concept dated 2009, which still fits in with later plans.

CBD North

From the 2011 business case:

Eleven potential station entrance locations were examined, including interchanging with Melbourne Central Station. The preferred option for interchange is a subterranean concourse under La Trobe Street linking directly to the existing and proposed concourses at each station. Entrances 2 (north-west corner of Swanston and La Trobe Sts) and 8 (south-west corner of Swanston and Franklin Streets) were assessed as the best primary entrances points accounting for passenger flows and known constraints. Entrance 9 (south-east corner Swanston and Franklin Streets) would be an alternative entrance to Entrance 8 if Franklin Street is closed to traffic east of Swanston Street. An entrance at the south-east corner of La Trobe and Swanston Street (State Library) (Entrance 1) is not proposed due to heritage considerations of this site. Consideration was given to a more direct connection with the heart of RMIT University on the east side of Swanston Street (3, 4 and 5) but not pursued to avoid disruption to RMIT’s main campus.

Figure 5-8 from the same document shows the concept for CBD North, with the station located north of La Trobe Street, with the tram tracks splitting around the glass roof that covers the concourse.

That design matches this circa-2012 artists impression of the station concourse.

It also matches this cross section diagram of the station, which was found in the media pack for the April 2015 announcement of the preferred shallow tunnel route.

CBD South

From the 2011 business case:

Twelve potential station entrance locations were examined. The option taken forward for the purpose of the 2010 business case was a ‘paid area’ subterranean concourse at the east end of Flinders Street, providing direct connection to the existing Flinders Street platforms via lifts (escalators were not considered feasible). During 2011, further options have been considered in the context of the shallower (high) tunnel alignment. A simpler connection between the subterranean CBD South concourse and the existing Flinders Street concourse is now proposed. The following entrances are the optimal locations: Entrances 3 (Swanston Street opposite St Paul’s) and 4 (City Square) are the recommended primary entrances.

Entrances 2 (Federation Square) and 6 (Flinders Lane/St Paul’s) are also deemed to be desirable to spread pedestrian demand to the east (less crowded) side of Swanston Street. Entrance 2 at Federation Square would be important in handling event patronage. Direct access to the south-west corner of Swanston Street/Collins Street was considered to better support this interchange but is not proposed due to the impact and cost of land acquisition in that location.

Figure 5-9 from the same document shows the concept for CBD South, where a single concourse is located directly above the station platforms.

Figure 5-10 shows how the concourse at CBD South with interchange with Flinders Street Station.

Further detail of the interchange passageway was found in the 2012 Flinders Street Station Design Competition Design Brief document. From the side:

And from the top:

The design matches this circa-2012 artists impression of the Collins Street entry at Town Hall.

But this undated view of the Flinders Street end is a little confusing – to me it seems to be showing the deep level option.

Domain

From the 2011 business case:

Twenty-three potential station entrances were examined. The preferred entrance locations are at 17 (corner St Kilda Road and Bowen Crescent) and 16 (corner St Kilda Road and Bromby Street). An additional direct access to the new tram interchange above the station in St Kilda Road is also proposed.

Figure 5-11 from the same document shows the intended ground level arrangement of Domain Station.

Again, a match for the circa-2012 artists impressions.

How to build it

With design decisions completed, chapter 5 of the business case then looked at the scope of preferred scheme.

Figure 5-3 provides a horizontal alignment overview of the tunnel.

Figure 5-4 shows the vertical alignment.

And Figure 5-5 shows the geological makeup along the route.

Characteristics and design parameters for the underground stations are presented in Figure 5-7.

Figure 5-12 shows the intended construction methods – mostly bored tunnels, with cut and cover work through the CBD, and immersed tubes under the Yarra River.

And Figure 5-14 shows potential site that can be redeveloped once construction in the CBD has been completed.

I’m sure glad the the full document finally saw the light – you can take a look at the full document here.

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