Headed in

The open day was held on the closed off section of Domain Road, east of Anzac station.

With food stalls.

And kids activities.

Including a train ride.

But the reason I was there was to see inside Anzac station itself.

Touring the station

We headed downstairs.

The Domain Road entrance having a single up escalator and a flight of stairs.

As well as a lift, that doubled as a light well.

We were then greeted by the unpaid area concourse, which passes beneath St Kilda Road.

And the tram stop above.

A trio of escalators and a lift connect the station concourse to the south end of the tram stop.

And a single escalator, steps and lift to the northern end.

The unpaid area walkway then continued west to the station entrance on Albert Road.

With a pair of escalators.

Along with a lift.

Down to the platforms

Now it was time to head down to the platforms.

Obviously no trains running.

But the passenger information screens had been installed.

Through the ticket gates.

With sunlight still streaming in from the glass roof above.

We went past the pair of lifts down to platform level.

And took the escalators down instead.

A wide island platform greeting us.

But still no trains.

Temporary fencing in place across the platform screen doors, with a demarcation still in place between active rail tunnels and the under construction railway station.

But network ‘strip maps’ already displayed.

Along with customer help points.

The big orange pendant light fittings also a design feature.

Along with the orange ceiling details.

It was then time to head back out again, so we took a trio of escalators back to the concourse.

And then back out of the same ticket gates we entered through.

Past the customer service counter.

Past the hidden away back of house area.

Back down the unpaid concourse towards Domain Road.

Back up the escalator.

And back into the sunlight.

Ending the tour.

Footnote: a few other things I noticed

Anzac station isn’t completely finished yet – the retail spaces are still taken up by temporary facilities for construction workers.

With a few bits of wall cladding also missing.

I also noticed a separate set of stairs beside the Domain Road entrance.

Locked away from public use, for firefighter access in case of emergency.

I also found a second lift door hidden away at the back of the Domain Road lift – presumably it leads into the back of house area of the station.

And on Domain Road the tram tracks have been rebuilt, with new platform stops installed – despite route 58 trams still using the tracks along Toorak Road West they were diverted along back in 2017 to make way for the construction of Anzac station.

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This is an incomplete list of infrastructure that has had to be modified, replaced or rebuilt due to underground mining.

A quick introduction to longwall mining

The Total Environment Centre provide us some background to longwall mining in New South Wales.

Longwall mining is a form of underground coal mining where ‘panels’ of coal are mined side by side separated by narrow ‘pillars’ of rock that act as supports.

A long wall panel can be up to 4km long, 250-400m wide and 1-2m thick. Chocks are then placed lines of up to 400m in length to support the roof.

Coal is cut by a machine called a shearer that moves along the length of the face in front of the chocks, disintegrating the coal, which is then taken by a series of conveyors to the surface.

As coal is removed, the chocks are moved into the newly created cavity. As the longwall progresses through the seam, the cavity behind the longwall, known as the goaf, increases and eventually collapses under the weight of the overlying strata.

This collapsing can cause considerable surface subsidence that may damage the environment and human infrastructure.

Longwall mining in NSW began in 1962. In 1983/84 it accounted for 11% of the state’s raw coal production. This had increased to 36% by 1993/94 and stood at 29% in 2003/04.

Nearly all of the coal mined in NSW lies within the Sydney-Gunnedah Basin and in the five defined coalfields of Gunnedah, Hunter, Newcastle, Western (in the Lithgow / Mudgee area) and Southern (in the Campbelltown / Illawarra area).

Virtually all coal mining in the Southern and Western coalfields is underground.

Douglas Park Bridges, Hume Highway

The first example of modified infrastructure I found was the 285 metre long twin Douglas Park Bridges, which carry the Hume Highway 55 metres above the Nepean River.

The concrete piers having a large steel brace attached where they meet the bridge deck.

The bridge was designed in 1975 by the Department of Main Roads, and did not take land subsidence into consideration, as the Department of Mines indicated mining that they would maintain a coal mining buffer zone around the bridge.

However by the late-1990s approval was given to BHP Coal to expand longwall mining at thier Tower Colliery towards the bridge, provided an extensive monitoring program was put in place.

The impact on the bridge once mining was complete – the abutments were 10 mm closer together, piers had sunk up to 18 mm, and the piers at one end had moved 48.6 mm east.

In the years that followed, the movement in the bridge had worsened, and so in 2007 BHP funded a $9 million project to realign the bridge.

The northern Abutment had moved 57mm, the first Pier around 40mm and the second Pier around 20mm. The next piers were stable.

Because of the different movements, the deck was in a unnatural form and that’s why the bridges had to be realigned. Works had to be proceeded with a minimum of bridge closures.

On the abutments, pot bearings had to be replaced with sliding bearings, which required 4 x 200 tonne jacks to lift the deck. To be able to lift the deck at the Piers, we installed a 40 tonne steel structure to create a lifting base around each Pier.

The realignment was done using 6 x 50 tonne jacks. Once the movement was complete, the bearings had to be welded or clamped to fix the deck to the Piers.

However while this work was still underway, the NSW Government approved further mining was approved beneath the bridge, but this time with a network of 400 sensors collecting deformation data 24 hours a day, along with inclinometers linked to an early warning system.

Trackside solar powered gizmos

Alongside the Melbourne-Sydney railway outside Picton, I found an multiple sets of solar powered instruments connected to the tracks.

And a few kilometres away outside Douglas Park, I found some more complicated looking systems.

Complete with fixed structures for the installation of surveying equipment.

These systems monitor movement in the railway due to mining at the SIMEC Group Tahmoor Colliery and South32 Appin Colliery respectively.

Risk mitigation on the Hume Highway

BHP Billiton Illawarra Coal’s Appin Colliery also passes beneath the Hume Highway at Douglas Park, with land subsidence running the risk of distorting the base of the road pavement. The solution – cutting up the road.

Modelling studies concluded that cutting slots through the existing pavement would be an effective method of dissipating compressive stress in the bound sandstone subbase. As a result of these analyses, the Technical Committee adopted a management strategy where slots would be installed prior to mining.

Sixteen slots were cut in the pavement, eight in each carriageway, directly above the proposed Longwall 703. A further twenty six slots were cut above Longwall 704, for which mining has now started. The spacings of the slots were based mainly on subsidence predictions, with extra slots added within a zone of geological structure.

The Technical Committee recognised that pre-mining slots would probably not be able to accommodate all potential subsidence movements. In particular, irregular subsidence movements could develop, the locations of which could not be identified prior to mining, resulting in locally high compressive stresses in the pavement.

The Technical Committee recognised that additional slots could be installed proactively during mining based on actual monitoring data prior to compressive stresses in the pavement becoming sufficient to result in stepping. Materials, labour and equipment were available to install a new slot within a required 48 hours, with a target to install within 24 hours. This was undertaken on 5 occasions during mining.

Fibre optic sensors were also installed to monitor the movement of the road surface.

BHP Billiton’s Illawarra Coal has embedded three kilometres of fibre optic cables in the Hume Highway to track subsidence caused by a longwall mine that runs under the road.

Illawarra Coal uses fibre Bragg grating sensors to measure temperature and strain at ten-metre intervals along the road’s pavement to detect any forces that could damage the road.

Illawarra Coal’s in-pavement monitoring system is connected to a site-based bank of interrogators that analyse the raw data on a real time basis.

“All data is transferred via wireless network link and is maintained on a web server which is managed by one of the key stakeholders,” a BHP Billiton spokeswoman told iTnews.

“The captured data is compared against pre-determined triggers and has the capability to initiate mobile phone SMS-generated alarms if required for appropriate response as determined by the trigger.”

Replacing a railway tunnel

Just outside of Tahmoor was Redbank Tunnel – a 315 metre long double-track tunnel completed in 1919 as part of the duplication of the Melbourne-Sydney railway.

Google Earth, April 2010

But there was a problem – the nearby Tahmoor Colliery, established in 1975, and expanded in 1994 and 1999.

A further 4.5 million tonnes of coal was located under the tunnel, and Xstrata wanted to expand the mine yet again to extract it, which would destroy the tunnel.

Tahmoor has now undertaken modelling of subsidence impacts on Redbank Tunnel as a result of mining. This modelling has concluded that subsidence impacts would be significant (up to 1130 mm of vertical subsidence) and likely would impact on the structural integrity of the tunnel, resulting in a risk to rail safety on the Main Southern Railway Line which runs through the tunnel.

So their solution – move the railway.

On 21 December 2010, Tahmoor submitted an application to the Department seeking to modify the Minister’s consent (DA 67/98) to allow for mining impacts within Area 3, and thereby to support the proposed mining of these longwalls. In order to avoid the potential impacts on rail safety, Tahmoor proposes to build a major deviation of the Main Southern Railway line for 1.9 km around the tunnel. The modification would also involve construction of a new overbridge to facilitate landowner access to their property once the rail track has been completed.

And decommission the redundant tunnel.

If Redbank Tunnel was left open after it is bypassed, then it is likely that some sections of the Tunnel’s masonry lining would experience cracking, shearing and localised spalling and possible collapses as a result of mining subsidence. Tahmoor therefore proposes to fill the tunnel with material excavated during construction of the proposed deviation, mitigating any potential safety hazards to people who might enter the tunnel and reducing subsidence to the natural surface above the tunnel.

Reshaping the landscape.

Assessment Report: Tahmoor North Mine, Redbank Rail Tunnel Deviation Modification

Work on the deviation commenced in June 2012, with the first train using the new route in December the same year.

Rebuilding a bridge

While chasing trains around Picton, a strange looking bridge caught my eye.

The expansion gap looking far too big for the size of the bridge.

It turns out coal mining at Tahmoor Colliery was also the driver here.

Tahmoor Coal Pty Ltd is currently replacing an existing bridge over the Main Southern Railway Line near Picton in NSW, due to proposed mining works. The new bridge is located immediately to the west of an existing brick arch bridge. The rail overbridge is an asset of Transport for New South Wales with Wollondilly Shire Council owning the connecting road.

The new overbridge is required because of potential subsidence impacts from scheduled longwall mining activities in the area in late 2015 which would compromise the safety of the existing bridge structure. The project also involves realignment of the road approaches and the demolition of the existing bridge.

A key issue in the design was the articulation of the bridge which had to cater for large opening/closure movements and large differential vertical and horizontal movements between the two ends of the bridge. A large movement modular deck joint and large movement sliding spherical bearings were adopted to accommodate these potentially large mine subsidence displacements.

Construction commenced in June 2015 and was completed by November the same year.

Landbridges on the Hume

This pair of bridges on the Hume Highway outside Mittagong don’t look at unusual from above.

Google Maps

Or from the road.

Google Street View

But they don’t actually span a watercourse.

Google Street View

But were built in 2000s to bridge a section of land affected by mine subsidence.

Plan to bridge the Hume Highway at Mittagong
5 June 2001

Working with the Federal Department of Transport and Regional Services (DOTARS), the Roads and Traffic Authority (RTA) has commenced preliminary work on the upgrading of the Hume Highway on the Mittagong Bypass.

The south and northbound lanes will be re-built and two new three-lane bridges constructed on this major interstate road corridor as a result of geological changes that have damaged the road surface and surrounding region over time.

To maintain travel conditions for the 16,000 vehicles using this section of the highway every day, the RTA will receive an initial $6 million from the Federal Government to complete planning and to construct median cross-over lanes. These will allow traffic to switch between the north and southbound carriageways once construction of the bridges has commenced.

The crossovers will be located near the Nattai River and Gibbergunyah Creek bridges and are expected to take two months to build.

During construction, lane restrictions will be in place in the area from 7am to 6pm Mondays to Fridays and from 8am to 1pm on Saturdays.

“In recent years, engineers have detected a subsidence in the road caused by the unique geology of the area. However, the current rate of ground movement is extremely slow and presents no short-term risk,” an RTA spokesperson said.

“The area has a very complex geological history, including mining activity at the adjacent Mount Alexandra Coal Mine from the 1950s to the 1970s.

“To ensure the highway continues to provide high standard travel conditions, work on the crossovers has commenced, with construction of the bridges expected to begin later in the year for completion by the end of 2002.”

The RTA expects to let a contract for the bridge works in October. The twin three-lane bridges will be supported by concrete pylons sunk 10 metres into the bedrock and protected from possible future earth movement by steel casings.

The southbound bridge will be built first and then operate temporarily as a single carriageway road carrying traffic in both directions during construction of the second bridge.

“The Hume Highway is Australia’s most important interstate road artery, with funding for improvements and maintenance a Federal Government responsibility,” a Department of Transport and Regional Services spokesperson said.

“Accordingly, the cost of the new bridges will be fully funded by the Federal Government.

“Both the Federal Department and the RTA are working to ensure this essential road route is upgraded quickly and with minimal inconvenience to the travelling public.

Telephone trouble at Tahmoor

Even the Telstra network wasn’t safe from mine subsidence at Tahmoor.

As part of the planning for mining longwall LW32, Tahmoor Coking Coal Operations has identified surface assets which may be affected by the mining operation in Tahmoor north area. Some of these assets belong to Telstra and are part of Telstra’s infrastructure in the area.

Telstra’s major assets in the area are: Tahmoor telephone exchange which is located on the north east corner of Thirlmere Way and Denmead Streets and Picton telephone exchange which is Menangle Street.

As mining has continued north of the telephone exchange the potential for impacts on the major network cable infrastructure has changed as now the longwalls are commencing to impact on the Picton telephone exchange area and the optical fibre cables and copper network to the south of Picton.

The planned longwall mining covering the area.

Management Plan – Longwall Mining beneath Telstra plant at Tahmoor and Picton NSW

With the critical parts of the network being:

a. Optical Fibre Cable – this is predominantly due to the nature of the cable in that it is only able to sustain relatively low ground compressive and tensile strains before the external sheath transfers the strain to the individual fibres within the cable. When this occurs the individual fibres have limited capacity to tolerate tensile or compressive strains before they cause interruption to or failure of transmission systems.

b. Aerial Cable – Aerial cable anchored at adjacent poles or from pole to building can be impacted by ground tilt. Where poles are affected by ground tilt the top of the pole can move such that there is a change in the cable catenery with the potential to either stretch the cable or reduce the ground clearance on the particular cable.

And somehow the legacy copper network got off lightly.

Generally the more extensive Main and Local copper cable network is more robust and able to tolerate reasonable levels of mining induced ground strain. The interaction is complex since the network comprises of very small cable of 5mm diameter up to heavily armoured 60mm diameter cables spread diversely across the entire mining area.

Footnote: and the environment

Water being lost to reservoirs.

NSW’s top water agency has called for curbs on two big coal mines in Sydney’s catchment, saying millions of litres of water are being lost daily and that environmental impacts are likely breaching approval conditions.

Cracks in creeks.

The ground is bulging and cracks are reaching from the surface to the coal seam in a section of Sydney’s drinking water catchment that sits above a mine, according to an independent study commissioned by the state government.

Creeks turning orange.

Flows from a “significant” water source for one of Sydney’s dams are turning orange and disappearing beneath the surface because of an underground coal mine that is slated to expand to beneath the reservoir itself.

180 tonnes of concrete pumped into a creek.

It was meant to be a remediation program to repair extensive mine subsidence damage to Sugarloaf State Conservation Area in the Lower Hunter. Instead it turned one environmental disaster into another. Contractors working for coal giant Glencore Xstrata pumped more than 180 tonnes of concrete into a tributary of Cockle Creek at Lake Macquarie.

And yet new mines are approved beneath reservoirs.

The Berejiklian government has given the nod for the extension of coal mining under one of Greater Sydney’s reservoirs, the first such approval in two decades.

The Planning Department earlier this month told Peabody Energy it could proceed with the extraction of coal from three new longwalls, two of which will go beneath Woronora reservoir.

All of this makes a few damaged bridges and cracked highways pale in comparison.

Further reading

• Mine Subsidence Community Guide (Mine Subsidence Board)
• Impacts of longwall coal mining on the environment in New South Wales (Total Environment Centre, 2007)
• Impacts of underground coal mining on natural features in the Southern Coalfield (NSW Government, 2008)

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Their start their life behind an anonymous gate in Ravenhall, next door to the Regional Rail Link tracks.

But the ‘tunnel lining segment manufacturing facility’ sign gives it away.

Overhead cranes travel over the casting yard.

Segments and a sunset. More than 1,500 concrete segments have been manufactured at our tunnel lining segment facility in Melbourne’s west. Our tunnel boring machines will use 56,000 curved concrete segments to create a watertight lining inside the twin 9km rail tunnels. pic.twitter.com/rCi0iIzOCp

— Metro Tunnel (@metrotunnelvic) July 22, 2019

Production started early, so that a stockpile of tunnel lining segments could be built up.

It’s no cornfield, but how’s the serenity? So much serenity.

Our tunnel segment manufacturing facility is in full production mode pumping out the 56,000 concrete segments required to line the Metro Tunnel’s twin nine-kilometre tunnels. pic.twitter.com/ZD1tva9YQ2

— Metro Tunnel (@metrotunnelvic) August 20, 2019

180 segments being poured a day.

The first segments were delivered in August 2019.

The first tunnel segments have arrived at the new North Melbourne Station site with 18 concrete segments delivered, each weighing 4.5 tonnes.

The TBM will use these segments to create temporary rings to line the steel bell, which is an innovative launching method for the TBMs. pic.twitter.com/QzOUQZxx4P

— Metro Tunnel (@metrotunnelvic) August 22, 2019

Driven across Melbourne six at a time on the back of a semi-trailer.

Until they arrived at the future North Melbourne station site.

In September work on the shed over the station box was still underway.

But was completed in October.

Ready to store the concrete segments, before they are lowered into the tunnel.

Loaded onto a rubber tyred TBM support vehicle.

Even the mightiest machines need some support

Meet our TBM support vehicles, tasked with delivering the concrete segments needed to line the Metro Tunnel and will eventually be used to transport our team to and from the TBMs. pic.twitter.com/5Nu2CiaYSE

— Metro Tunnel (@metrotunnelvic) November 13, 2019

And driven through the tunnel to the TBM itself.

TBM Joan is on her way towards Kensington, installing a number of tunnel lining rings, composed of concrete segments. The team has been monitoring Joan’s performance and systems, including confinement pressure management, ring building, segment handling and grouting. pic.twitter.com/Hsa9dVdZ2f

— Metro Tunnel (@metrotunnelvic) October 6, 2019

Which then assembles them into a tunnel wall.

A sidenote on the gantry cranes

The gantry cranes at the casting yard were supplied by Australian manufacturer Eilbeck Cranes, as were cranes at the Melbourne CBD worksites.

Those cranes seem to be more successful than those at Parkville station – dismantled due to safety concerns.

Meanwhile on the West Gate Tunnel

The West Gate ‘Tunnel’ might be predominately surface roads, but it actually features two tunnels: 4 kilometre long outbound and 2.8 kilometre long inbound.

The precast concrete segments for this project are being manufactured by LS Precast in Benalla, served by a dedicated rail siding.

https://www.youtube.com/watch?v=5pEzo0HCfBY

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The first problem

Walking along the tracks will take forever – each section of concrete slab track has a hole in the middle!

So emergency trolleys were provided at each entrance to the loop, ready to be clipped together and then pushed down the tracks.

But it’s a long way to push a trolley between stations.

And a better solution

So in 2009 the first motorised Rail Network Emergency Response Vehicles were delivered.

Ambulance Victoria photo

The Department of Transport wrote about the new vehicles in their 2009-10 Annual Report (dead link).

Victoria now has 12 Rail Network Emergency Response Vehicles (RNERVs) located at stations along Melbourne’s underground rail loop and other strategic locations. The vehicles are used in emergencies to ferry emergency personnel and aid to the scene of an incident. Nine of the vehicles were purchased in 2009-10.

To test the vehicle’s capability, a simulated emergency exercise – Exercise Orpheus – was held in April 2010. In the exercise, a major emergency was constructed based on a train stranded between Flagstaff and Melbourne Central Stations. To test their performance and suitability, the response vehicles were sent from both stations, transporting emergency services personnel from Victoria Police, Melbourne Fire Brigade and Ambulance Victoria.

Ambulance Victoria also wrote about their first test run.

Welcome to a training exercise involving Melbourne’s emergency authorities that aims to test their preparedness and response to an attack on major infrastructure.

The recent exercise also tested a mobile platform developed by the Department of Transport that can quickly be assembled, then take emergency workers into the Loop and be used to carry patients to safety. The platform, known as the Rail Network Emergency Response Vehicle, is assembled and operated by members of the Metropolitan Fire Brigade.

‘The Loop presents unique challenges because it is not a road and there are only limited access points, which makes it difficult for paramedics to access,’ said Jon Byrne, from Ambulance Victoria’s
Emergency Management Unit.

‘This new platform had been tested in the rail yards, but this was its first use in a training exercise. We wanted to ensure it could take us there and back, plus bring out patients and we were pleased with the results.’

Each vehicle is stored in a cabinet.

Then moved in pieces to the track.

Ambulance Victoria photo

Bolted together.

Ambulance Victoria photo

And driven along the tracks to the incident site.

Ambulance Victoria photo

Battery powered, the British developed Bance motorised hand trolley weighs 121.75 kg, with the heaviest section weighing 53.5 kg, and capable of carrying 1000 kg of loading at 8 km/h up to 25 km.

R. Bance and Co. photo

Now skyrail

Fast forward to today, and Melbourne now has elevated rail tracks – another difficult to access location.

But the solution is the same – a portable battery powered trolley.

Rail Express photo

But advanced in technology have seen the weight of the trolley drop, while performance has improved.

In December 2018 Rail Express wrote about this Australian-developed rapid deployment trolley.

Rail equipment manufacturer and distributor Melvelle Equipment has developed a cutting-edge rapid deployment rail trolley, manufactured in Australia and already in use on the busy Melbourne Metro network.

The self-propelled trolley can travel up to 100 kilometres with a full payload of 700 kilograms. At its maximum speed, it can travel up to 80 kilometres.

Despite this impressive range, the machine is just 160 kilograms including batteries, and can be assembled by two people in just three minutes, with no tools required. Four people can assemble the machine in just two minutes.

The machine can be removed from the track in three minutes by two people, or as little as 90 seconds by four people. Its heaviest component weighs just 40 kilograms.

The first units of the trolley were delivered to Metro Trains Melbourne in March 2018.

“The Level Crossing Removal Authority approached us regarding the need to have emergency response vehicles at every train station for the overhead [skyrail] system, because you can’t drive a truck up there,” Melvelle explains.

“The machine is stored at the stations, and if there’s an emergency the responders can wheel it out of the storage area, set it up on track, and travel down the track to the emergency, bringing all their service gear – for example a stretcher – and their people.”

Hand throttle via joystick including horn, traction control, regenerative braking, dead-man pedal, emergency brakes, and full interlocking of all parts of the assembly, meaning if a wheel or a handrail is not correctly installed, the trolley will not move and a light panel will display the location of the error. There are two sets of controls on the trolley, but only one joystick, which must be moved by the operator in order to change direction, up or down the railway.

Melvelle says his company plans to export the product, with interest already registered as far away as UAE and England for the system.

“The trolley is designed manufactured in our factory in Newcastle and I it is the lightest and safest trolley on the market,” he says.

Who said Australian innovation and manufacturing was dead?

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CityLink consists of two tunnels – the shorter Domain Tunnel that carries westbound traffic, and the longer Burnley Tunnel that carries eastbound traffic – with roadheaders being used to construct the majority of each tube. However at each end of the tunnel, the project faced the same problems as the Melbourne Metro tunnels.

At the western end of both tunnels is Grant Street and St Kilda Road, full of both road and tramway traffic.

Here a ‘top down’ methodology was adopted while digging the massive hole.

Excavations for cut & cover works at Grant Street May 1998 (Ian Hill, SLV image H99.20/24)

The 2002 book Journey and Arrival: The Story of the Melbourne CityLink published by the Institution of Engineers, Australia elaborates:

The conventional cut-and-cover method was not used at the Grant Street portal, in part to accommodate the impact on the adjacent Victorian College of the Arts (VCA). The size of the excavation necessary for cut-and-cover was huge: 35 metres wide and progressively increasing in depth to about 25 metres at St Kilda Road.

The top-down technique used along Grant Street involved the installation of columns along the alignment of the outer walls of the tunnels, and along the centre line which would ultimately form the barrier between the two tunnels. This was achieved by drilling holes about 900 mm in diameter to bedrock, and then backfilling the holes with concrete. A concrete beam was then constructed along the top of the columns to form the support for the tunnel roof. Once the spans were in place, Grant Street was reinstated and excavation took place unimpeded beneath the deck.

The top-down variation of the cut-and-cover method also reduced the disruption on St Kilda Road, a major thoroughfare with busy tram lines. In fact tram services were closed on only one weekend. The crossing of St Kilda Road was undertaken in stages. Initially the outer service roads were closed and traffic was diverted to the central roadway. This allowed the construction of the columns and tunnel roof in the same manner as along Grant Street. However, extensive propping was necessary under the surface to support the columns against the 25 metre depth of soil pressure. Once work on the outer service roads was completed, traffic was re-diverted to allow work on the central part of the road.

Meanwhile at the east end of the Domain Tunnel was the Yarra River, which passed only a few metres above the future tunnel roof.

It was decided to build the river crossing in two stages, with a coffer dam being used to keep the water out while allowing the river to keep flowing.

Coffer dam construction in Yarra River for Domain Tunnel 26/4/97 (Ian Hill, SLV image H99.20/10)

Again, Journey and Arrival: The Story of the Melbourne CityLink gives the technical details:

The construction of the cut-and-cover crossing of the Yarra River represented some of the cleverest engineering of the whole project. Essentially, a trench had to be cut in the riverbed, the tunnel built in it, and the riverbed placed back on top.

As these works could not proceed easily underwater, the river had to be diverted away from the riverbed worksite during construction. The most efficient way to do this, while ensuring minimum disruption to river flows and traffic, was to work on the crossing in two parts: initially shutting off about two thirds of the river from one bank, and, when completed, switching to the other bank, then closing the other third of the river to complete the process.

What does it mean for Melbourne Metro?

Back in April 2015 how to built the Melbourne Metro tunnels beneath the Yarra River was still unresolved – possible solutions being an immersed tube tunnel, or CityLink style cut and cover using a coffer dam.

This week the final solution was announced – a tunnel boring machine would do the work, with the tunnel running to the east of Princes Bridge, around seven metres below the riverbed, and 11 metres below the surface.

More photos of CityLink

The State Library of Victoria holds the ‘Melbourne City Link Project Series‘ – images taken by photographer Ian Hill during the construction of CityLink.

• Concrete pour for roof of Domain Tunnel inside coffer dam in Yarra River
• Grant Street entrance for Domain Tunnel showing cut & cover works
• Entrance to Domain Tunnel at Grant Street

There is a lot more technical details in Journey and Arrival: The Story of the Melbourne CityLink – I’ve just scraped the surface in this post.

VicRoads also have an interesting CityLink related document on their website – Exhibit I Project Scope and Technical Requirements.

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The City Loop consists of four tunnels over two levels: platforms 1 and 2 on the upper deck serve the lines through Clifton Hill and Caulfield, while platforms 3 and 4 on the lower deck serve the lines that pass through Burnley and North Melbourne.

The process

Unfortunately detailed diagrams of each City Loop station aren’t accessible online, which rules out the obvious way to read the depth measurement. Firing up the GPS on your phone could be another way, but getting a fix on the satellites from underground is impossible, and even if you could – the altitude accuracy of a consumer GPS device is about +/- 15 meters!

I ended up turning to another set of diagrams – the railway issued ‘Grades and Curves’ book that shows the general alignment and elevation for each of the City Loop tunnels. (the full set of diagrams can be found at Vicsig)

The diagrams in the ‘Grades and Curves’ book are used to assist train drivers in learning the routes they will be driving along – trains don’t accelerate and stop like a car, so knowing about sharp curves, long inclines and steep descents is essential to keep the train under control.

Unfortunately the Grades and Curves diagrams only include elevation in metres above the Low Water Mark – a datum set as the level reached by seawater at low tide – and not in metres below the surface!

To determine the ground level elevation of each station, I turned to the survey marks database operated by Land Victoria. It gives the elevation of thousands of survey points around Australia, all given in relation of the Australian Height Datum (AHD) – a height set to the mean sea level for 1966-1968 calculated at thirty tide gauges around the coast of the Australian continent.

With the depth of each platform given by the Grades and Curves diagrams, the ground level elevation from survey marks, and the the rest is just simple arithmetic.

Flagstaff Station

For Flagstaff station the Grades and Curves diagram states the upper level is at +8 metres LWM, and the lower level is at -1 metres LWM. William Street is at the crest of the hill, so survey mark ‘MELBOURNE NORTH PM 50 MURLA’ (#308300500) on nearby Little Lonsdale Street can be used, located at a height of 28.446 metres above AHD.

Melbourne Central Station

For Melbourne Central station the Grades and Curves diagram states the upper level is at +2 metres LWM, and the lower level is at -7 metres LWM. La Trobe Street is a complicating factor – the Swanston Street end being higher than than that at Elizabeth Street – so I looked at two survey marks – ‘MMB 380’ (#450003801) on the Elizabeth Street corner is at 13.450 metres above AHD, while mark ‘MMB 388’ (#450003881) is located at a height of 22.370 metres above AHD.

Parliament Station

For Parliament station the Grades and Curves diagram states the upper level is at +7 metres LWM, and the lower level is at -3 metres LWM. Spring Street is relativity flat atop the station, so I used survey mark ‘MELBOURNE NORTH PM 16 MURLA’ (#308300160) on Lonsdale Street, located at a height of 36.746 metres above AHD.

So what have I discovered?

• Parliament station is the deepest below ground (39.5 metres) on the City Loop
• Melbourne Central is the furthest station below sea level, but is the closest to the surface (between 20.5 and 29.5 metres) due to Elizabeth Street being in a valley
• Flagstaff station is the highest station above sea level, but is the second deepest (29.5 metres) due to the location atop a hill

Checking my answers

After doing the maths myself, I remembered that the Metropolitan Transport Authority put together a booklet of City Loop facts and figures in the mid-1980s.

It quotes the following depths:

• Parliament station: 40 metres
• Flagstaff station: 32 metres
• Melbourne Central station: 22 / 29 metres

I was out by 3 metres for the depth of Flagstaff station, but for the other locations, my roundabout way of determining the City Loop depth was reasonably accurate!

An alternate method

Another method to measure the depth of an underground station is to measure the height of an escalator step, count the total number of steps between platform level and the surface, and multiply them together to get the total height.

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