DART underground - options

murphaph

Yeah I know, which is why I think a sub surface station at SD is basically dead. There are easier places to build a DU station than under the new SD station. But the plan was originally to surface just north of the new SD station and tie in to the existing docks branch around Church Rd. Junction. The same gradients are involved more or less. Here in Berlin the regional trains (push pull, not EMUs!) manage what appear and feel like very steep gradients in comparison to what is often described as impossible in Dublin:

https://maps.app.goo.gl/euLXt6V2K8fGknvJ8

That regional line emerges from a sub surface station under Hauptbahnhof and climbs out up and over other railway lines and a set of roads including one road that is itself on a bridge over the railway.

Aside: I don't like the idea of surfacing as far north as Clontarf Golf Club without an intermediate station. The tunnel would be several km long from Killester to say GCD with no stations. At a certain stage you reach a point of diminishing returns. Clontarf Road would require some alternative service pattern if DU cuts it out of the loop. I think it's worth the effort to surface the tunnel south of Clontarf Road station.

More generally….To be honest I think Dublin is a pretty easy place to tunnel under. It's mostly flat with hardly anything under the ground. Sometimes I get the feeling we like to make mountains out of molehills. There are countless examples of this stuff done under tighter constraints.

An alternative would be to surface around Hawthorn Avenue and let DU have the existing docks branch, tying straight into the slow lines of four north (eastern pair), and creating a new pair of docks tracks slightly to the west of the existing ones. Remember the existing gradients were built for steam locomotives. The locos of today have significantly better tractive effort. The port hardly sees any freight trffic anyway, so a banker engine could be used if required (unlikely IMO, especially if the freight loco is electric). The port itself may not even be there in a generation.

Getting up over the Tolka eliminates the issues around the Port Tunnel and keeps Clontarf Road in the new network so it doesn't need extra services all for itself. If CPOs are required they would be low cost relative to the project. The houses along the railway embankment there are all max 2 storey dwellings. It's not like they'd need to CPO office or apartment blocks.

riddlinrussell

I'd say a rough sketch would help visualise what you have in mind, but the space seems a little too constrained to fit everything with a reasonable incline and curvature (no station to deal with simplifies things OFC!)

AngryLips

Couldn't they make use of all the land beside East Wall Road that was reserved for the southbound port tunnel which has since been scrapped? Of course the tunnel would need to be oriented in such a way as to necessitate an almost 180 degree bend, but a tunnel emerging from there that's oriented northwest would have a pretty clear path across Alfie Byrne Road towards the Northern line in Fairview Park - no?

murphaph

It would also be possible for emerging DU tracks to cross the Tolka at a lower level than the current railway bridge by dropping East Wall Road down or closing it to motorised traffic and sending that traffic around the Alfie Byrne Road/Fairview way. There is definitely a way to surface DU before Clontarf Road station.

bk

Just remember that the Dublin Port Tunnel is built across Alfie Byrne Road and Fairview Park, so any route around there needs to get up and over the tunnel.

PlatformNine

How deep is the port tunnel at Fairview Park? Surely at least 20-25m?

I have no idea how much deeper DU would need to go under the port tunnel but I can't imagine it being any less than an additional 5m. Assuming DU would be 25-30m below the surface and a grade of 2.5% (keep in mind the current maximum on the network is 1.67% based on the network statement) the tunnel would need 1-1.2km to surface which Fairview Park just doesn't have. I also feel that 5m is a very conservative guess and that it might need to be even deeper than that.

I think if the SD/Docklands portal is not longer feasible and/or they look at other portal options, the next available location is going to be Clontarf Golf Course. Though this would likely mean that either Clontarf Road Station would loose DART services or they would need to built a new underground station adjacent to it.

DaBluBoi

Is it also possible to start a portal in Connolly, or are the rail lines too tall for a tunnel to be easily inserted?

gjim

How deep is the port tunnel at Fairview Park? Surely at least 20-25m?

25m? No chance, surely?

It's fully above ground before it even leaves the park - in fact it's raised a few meters above ground in order to bridge the Tolka:

The entire section under Fairview park was constructed by cut n' cover - the cut n' cover "scar" through the park is clear in the map above. So the range of depth would be zero (or slightly elevated) at the Southern end, to a max of 10m at the Northern end.

I think the best chance would be for the DU tunnel to approach from the east of existing tracks - around where the port tunnel itself emerges in the red box above. If it can get under the Tolka to get into the park, then there's no issue with getting under the Port tunnel in this area.

However you've now got about 500m before Clontarf Rd (the road itself). To stay under, say, a 3% incline limit, and if you want 200m platforms in Clontarf Rd, you might need to re-do the bridge over Clontarf Rd - and effectively shift the platforms northwards - might not be a bad idea anyway, the current station's entrance is not particularly convenient.

I think the Golf club idea would probably be simpler from a construction perspective, but losing a DU station by going further north - as someone else says - would be a significant loss of utility for the system.

KrisW1001

There’s effectively no space between the tunnel and the tracks. During construction of the Port Tunnel, a supporting arch was constructed under the tracks using a technique called “pipe-jacking”: basically, the first section was slid in underneath the tracks, and then the next one pushed that one further in, and so on until there was a complete structure underneath.. The tunnel was then dug out underneath that arch.

As a result, there’s only about 3.5 m of earth between the top of the tunnel structures and the bottom of the railway structures. If you want to be at ground level at Fairview depot, then your only option is to surface south of the Tolka river.

The docklands site is around 1 metre above sea level, the rail bridge over the Tolka is at around 6 metres above sea level, and Fairview depot is at about 5 metres above. You’ll need a tunnel to be around 15-20 m below sea level, so the total rise needed is something between 21 and 26 metres. From Sherriff Street to the south side of the Tolka, there is about 780 m of track. That’s a gradient of between 2.6% (to rise 21 metres) and 3.33% (to rise 26 metres) depending on how deep you put the tunnel - 2.6% is entirely normal, and 3.33% is well within the capabilities of electric trains.

Brightlights66

https://www.boards.ie/discussion/comment/123619835#Comment_123619835

Of course it was, as you say, insane.

In terms of manpower and materials it would have been, effectively, an 8(eight)-level metro station.

However, it did get complete approval from ABP, in the form of the metronorth Railway Order.

loco_scolo

I think it would be possible to achieve the required gradient for a tunnel by starting the incline close to East Wall Rd along West Rd, rather than after Ossary Rd as per previous plans.

However this still doesn't solve all the issues that the new surface level Dart Station at Spencer Dock creates. The planned Dart Station has deep foundations sufficient to support an over station tall building, so tunnelling under this in future is not possible.

The options selection report for Spencer Dock Dart discusses the issue.

Annex-9-3-Docklands-Station-Options-Study-Summary-Report.pdf

riddlinrussell

I think the majority of people discussing DU in this thread now consider Spencer Dock Station (or any routing through/under it) to be somewhat dead in the Water.

The question is mostly, free of the now "shackle" of Spencer Dock, what routing gives the most benefit?

• Is it possible to Surface at/near the existing Docklands station and still provide a grade separated tie in to the Northern slow lines?
• Come up before the Tolka?
• Come up in Fairview Park? (Likely not due to port tunnel)
• Come Up at Clontarf Golf Course?

PlatformNine

https://www.boards.ie/discussion/comment/123635815#Comment_123635815

I didn't realise that the Port Tunnel was that shallow under the track bed, however that's still too much of a rise to make in such a short space. 3% max grade over 500m still only allows for a 15m rise. That just isn't enough, at the very least the station would need to be pushed north of Clontarf Rd, and I would still be very skeptical that 15m would be enough to clear Clontarf Rd without building a second lower bridge.

CatInABox

I don't think that the station could be near Clontarf Station/Fairview park. It's just not got enough room around the to do it easily, and "easily" equates to low risk and low cost for TII, something that is very high on their priority list these days.

If it's not going to be Spencer Dock, then I'd say the nearest place for a tunnel portal has to be Clontarf Golf Club. Considerations for that would be what happens with Clontarf Dart station itself, would you need to create another Dart Underground station there? There's also the River Wad in the Golf Club, which has flooded twice in the past 20 years and overflowed the dart tracks. Not insurmountable, but definitely a consideration.

PlatformNine

https://www.boards.ie/discussion/comment/123637266#Comment_123637266

I think removing a station from the network would be a very hard sell, I think they would have to build a DU Clontarf Road station.

It does however have the benifit that it could be much better located than the existing station (being closer to the road itself), could be built cheaper and shallower as a C&C station. Also if they try and build DU along side 4N it could avoid having to run 4 tracks through Fairview Depot.

As for the golf course, building the portal there I think is the perfect opportunity to redevelop the site. I would personally like to see it turned into a mix of housing and maybe also a new park, then build a new DART station to support development. The new station may sound a bit far fetched but there is almost 2km between Clontarf Rd and Killester and redeveloping a site that large could a few thousand people.

riddlinrussell

A cheaper C&C at Clontarf Road would be a really interesting proposition for sure, as you say, an opportunity to provide much better access to the station, provide the surface level station, to split the Killester/Clontarf distance with the surfacing station as well.

I'd say running 3/4 tracks as far as Fairview in that scenario would be no harm if it wasn't stupidly expensive as you could then still use it for Dart servicing/stabling and run Northern line Darts into Connolly/Spencer Dock without interfering with the fast lines, in specific circumstances.

CatInABox

https://www.boards.ie/discussion/comment/123637592#Comment_123637592

On the stupidly expensive part, from Clontarf Golf Club grounds onwards is probably going to be on the expensive end of the scale, with two bridges between there and Clontarf station. One of those bridges is a very old, some would say historical bridge, so there's very little chance of easily widening it, and there'll be objections galore if they choose to put another, newer bridge in front of it.

riddlinrussell

I mean, if that's unworkable I suppose you could have a tunnel siding and lift directly up into Fairview depot for servicing, bond villain style if we are really getting the crayons out 😅

jlang

Irish Rail have enough lifts out of order without needing them to get the train onto the track!

KrisW1001

Spencer Dock underground isn’t dead, but it has become a lot more expensive. Foundations for the station go down to -10 m, but a tunnel could still be routed under that. The big cost would then be to mine out the platforms, and the access passages, stairs and escalators down to this deep station. The advantage of doing it here is that you don’t have to provide the large public concourse and access halls, which would be phenomenally expensive to build from scratch for a deep station.

The option of preparing the void under the station ahead of DU (option 2b) was rejected not only because it’s really, really expensive, but also I think it was because there’s only one use for such under-basements: car parking - and provision of a large amount of car parking would be directly against Dublin City’s traffic planning guidelines for this part of the city. Why request planning for something that you know can never be granted planning?

There are solutions to digging under live railways. They’re expensive, but they’re possible, and the presence of a through line in the Docklands may be worth much more than the cost of providing it. Certainly if I was offering a property developer a chance to build over a station, having that station accessible directly from the Kildare and Meath commuter belts would get me a much bigger price than just offering a connection to North Kildare.

I think Four North will be what reveals the fate of DART Underground, because it’s this project that will facilitate (or hamper) any future DART tunnel.

loco_scolo

https://www.boards.ie/discussion/comment/123638381#Comment_123638381

I don't think it had anything to do with parking TBH. Every office/apartment block in the city has underground levels, which are not just for parking, but are also used for some utilities, deliveries, service vehicles etc.

Unless you go very deep under Spencer Dock Dart, I don't think it will be possible. The options selection report stated that the soil in that location won't allow a cavern to be mined after the fact. But who knows how factual that really is.

There is a clear clash between the proposed station and the DU station as it will be located beneath. It is not possible to construct the DU station once the Docklands Station is built because the soil does not have suitable characteristics to allow excavation of a cavern beneath the station at the level the DU station platforms are located.

The only way of designing the required layout for this Option and avoiding the demolition of the platforms to construct the DU project is to undertake first the civil works of the DU station that are not excavated as a tunnel.

murphaph

There really was no good excuse for not allowing for DU in the SD design. Yeah it would have cost more but saved a load of money in the long run but electoral cycles are short lived.

Consonata

https://www.boards.ie/discussion/comment/123639418#Comment_123639418

If you wanted better evidence that the state has given up on the concept of DU, you have it there to be honest. The moment they reopened the PPT, I felt DU was dead.

Zebra3

https://www.boards.ie/discussion/comment/123639675#Comment_123639675

Nope. PPT was a great short term solution, but not the final one.

Likely many of us won’t see the end result, but DU or some Metro tunnel feeding the south city centre will be eventually built.

murphaph

https://www.boards.ie/discussion/comment/123639675#Comment_123639675

It won't die easily though because DART+ and FourNorth and Luas and Metrolink and BusConnects will just bring more users to public transport. They will then start demanding further significant PT improvements from their politicians. DU will eventually be built because it's a complete no-brainer and has been done countless times before because it's such a no-brainer. We still do PT for slow learners but metrolink (if it goes ahead) will be a paradigm shift. Underground railways just aren't a thing in Ireland, but post ML they will be.

KrisW1001

https://www.boards.ie/discussion/comment/123639082#Comment_123639082

Point taken re: parking, but I suspect it would have been yet another mark against the plan if it went forward.

I think that DU will be very hard to “kill”. The only argument against it that stands up is that it will be very expensive. Nothing else really meets the need. The Phoenix Park Tunnel doesn’t have the capacity (although DART+ will improve its running speed). A Metro cannot replace DU unless you run that metro out the the suburban stations of the DART North and SW lines: something that will come in at a higher cost without increasing catchment area. Leaving things as they are (basically DART+) will buy another decade at most, but I think the lines upgraded by DART+ will see a huge increase in passengers, and that will drive the demand for an expanded service. If DART+ quickly exceeds projected ridership figures, that will put DU back on the table, but with a much larger rail commuter population to make the case for it.

Metro will show what underground rail does for a city. The DU plan just needs someone to publicise the fact that it’s an option. Once they know it’s possible, then the public will ask for it.

VonLuck

Are there diagrams of the feasible options for DU? I'm finding it hard to visualise where people are suggesting it could be routed.

riddlinrussell

Most recent feasibility study was the Dart+ Tunnel one, now dropped from the Dart + information website

https://www.nationaltransport.ie/wp-content/uploads/2021/11/DART-Tunnel-Route-Options-and-Feasibility.pdf

Note that the only southwest to north scenario considered there that doesn't go via Docklands ends up at fairview, but goes entirely via the northside and has low demand as a result. No south/central Dublin routings considered Fairview/Further north tie ins

Most of the discussion here re-further north tie ins is trying to avoid the complexity/challenge of tying in to the Northern line in/around the most junction heavy section, and reducing the curvatures and inclines of the route.

Basically what will minimise long term conflicts and limitations and maximise train speeds and frequencies.

Cost is important but secondary, and you'd hope if the cost differences weren't enormous then the engineering reports at least would agree, even if politicians didn't.

That report, interestingly always says tie-in at Docklands not Spencer Dock, though that might be being used as a generic catch all term for the area.

gjim

https://www.boards.ie/discussion/comment/123640140#Comment_123640140

I think that DU will be very hard to “kill”. The only argument against it that stands up is that it will be very expensive. Nothing else really meets the need. The Phoenix Park Tunnel doesn’t have the capacity (although DART+ will improve its running speed).

I think so too but I also think DU has a serious image problem to overcome because of its association with DART.

Irish Rail themselves - fairly and sometimes unfairly - are not seen as modern/efficient operators. And the while the current DART service is pretty good to be fair given its limitations, for me it has that unfashionable 1980s dowdy vibe about it. Many of the stations are awful both functionally and aesthetically, even some of the most important ones in the city like Tara and GCD, and feel like relics of pre-celtic tiger Ireland. Frequency is patchy, reliability is so-so.

All of these factors make the DU a difficult sell to the general public and thus politicians as it's difficult to convey how it would radically transform rail travel in and around the city. I view DU as creating two new high-capacity, high-speed, through-running metro lines that cut through the centre of the city - with less than 5 minute headways. Once you get to these sorts of frequencies, then heavy rail and light-rail metro systems are indistinguishable from a passenger's point of view. Crossrail in London got rebranded as the Elizabeth Line - as if it were just another tube line. In cities like Paris and Madrid, you switch between heavy and light rail "metro" without even thinking about it.

And the two lines that DU creates complement Metrolink really well in terms of coverage. Considering DART+DU and ML together, you've got a high speed, high capacity, well-connected rail network of over 100 rail stations offering amazing flexibility in terms of connections.

But this exciting vision has to overcome the current image of DART.

Consonata

https://www.boards.ie/discussion/comment/123643202#Comment_123643202

It doesn't help when the last major study into Dart+ rtunnel showed really poor benefit for €