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Sunday, 11 April 2010

Time for some Drainage

The blog post titles just get more gripping, eh?

When first visiting the excavation just a few weeks ago at the end of a cold March day, I remarked that the new excavation was drier underfoot than I expected. The person in charge pointed to a strip of freshly exposed stuff that looked much the same as the rest: 'There's a drain'. I'd not noticed the filled trench - filled with rather grubby railway-ballast-sized stuff, and not easy to see for the uninitiated. The contractors would have continued to put their observational skills to work for the following weeks as they excavated and in some places rearranged the material in the cutting, when they weren't prising it off the tunnel portal. Something's coping, because even the downpours of Good Friday didn't produce more than a puddle or two, though the excavation ran with water. It's obviously going somewhere.

Last Thursday evening provided a complete contrast to late March. It turns out that Devonshire Tunnel's cutting positively basks in evening sunshine, and the excavation was warming up nicely and exuding a fragrance that we'll kindly say was 'Earthy', and will in any case mellow in due course. Glancing light revealed the topsoil spread on the sides to have a thin covering of spider silk. A couple of crows were giving the ground the once over, while the badger sett entrance some way above the tunnel has seen the first small eruption of earth from its mouth for some time.

But, to progress. The contractors have for the most part shaped the down ramp to the tunnel, and much of the spoil that will be removed has now gone from the site. In the photos you'll see two part-completed fenced trenches running out from the tunnel portal. Revisiting, the following evening, the trenches had been extended and then filled with ballast-sized material - new drains to help keep the foundation of the down ramp good and firm. These will take water down the slope and out of the fill, it will then flow into the existing drainage which runs fairly energetically beneath the remaining material in the cutting.

The last two photos are from Friday evening, one shows the tunnel portal and newly filled drains - this image is taken 'Through the fence' from Linear Park - the work is for the present now thoroughly visible from there (with plenty of passers by stopping to look, some of them particularly curious because they remember the tunnel being buried). It will be good when this section is complete and in use as it's going to appear particularly pleasant as well as being dramatic. Chatting to two teenagers who were sitting by their bikes on a fallen tree down by the earth bund observing the goings on (been there done that), they said that while they'd been through Combe Down Tunnel on last year's open day, they couldn't wait to use the entire route.

(If you're interested in a Combe Down Tunnel open day, do put the 17th July in your diary and keep an eye on the web site)

The contractors will now be on site for around another week, and that will be the first work complete - the project's planning then indicates a hiatus for a month or so - preparations for the next stage of building the Two Tunnels route. They still have a little materials moving to complete, some of the ground has thrown up sections of brickwork, perhaps from demolished bridge once again. Much of this part of the route was built either in open country or on the edge of the built up area of the city, and both of the demolished bridges (and the surviving original arch of Claude Avenue overbridge) weren't originally built with the idea that they would cross urban streets - they were more of the nature of accommodation bridges, their traffic-constraining dimensions unfortunately ensured that they have not survived.

The underbridge that has survived is the three arched structure, Englishcombe Bridge, with a really strong flowering Blackthorn at one end of this - and the viaduct walks you straight past it at tree-top height. The viaduct was photographed to good effect by the author of the 'Forgotten Relics' web site - but here's 'Forgotten Relics' on the Devonshire Tunnel excavation.


Matthew Holbrook said...

Another very interesting update Mark. Thank you.

Anonymous said...

It doesn't look as if they have excavated down to the previous track bed as it left Devonshire Tunnel. Is it different in real life i.e. they are down to track bed and then it begins its slope up to Maple Grove Bridge?

John Yeo said...

Thanks for the continued update, Mark.

Mark A said...

@Anonymous: indeed - immediately outside the tunnel the level, for now, is still a little higher then the original trackbed.

It's possible that that's because the contractors won't work close to the (functioning) drain that's there until such time that the tunnel's block wall comes down, at which point they'll lower the ground to its final intended level - which within the tunnel itself will be at the level of the original trackbed.

The interior of the tunnel is still ballasted (and still has sleeper indentations despite both rails and sleepers having been removed in a rough and ready fashion some forty two years ago. Luckily the tunnel drain doesn't appear to have suffered in that process.)

From the tunnel, the ramp climbs at 1 in 20 above the original level beneath the spoil, the rest of which actually stayed put - the climb carries on as far as the current entrance to the public open space alongside the route, and the path will then slope down once more to regain the original level of the trackbed just beyond the bridge itself.

John Yeo said...

Blackthorn, Mark (!)

Mark A said...

@John Yeo. Oops, thanks for this. Now corrected.

stanley mayer said...

Good morning Mark.I am thinking back 4 weeks a go when we all stud there right on top of the Tunnel.
And now well its hard to take in what we all were standing on, great
well done to you all.
We are looking forwad to having another look this coming saturdsy.
I hope it dosen't rain

Dan Gallo said...

It's nice to see some good progress has been made!

Does anyone know if there's a planned completion date for the tunnels project? i.e. When does it open for use?

I cycle from Frome in to Bath, so this will be a great time saver!

Blockbell said...

Just had a look yesterday with a real lump in my throat, and went home to look again at Norman Lockett's superb colour shots of down expresses slogging up to Maple Grove and into the tunnel.
The growth of trees around here is very striking, with the consequent loss of the view across the rooftops of Bath.
Taking the point about the navigational needs of our good friends the bats, is there any possibility of opening any of this up again? The last time I walked up the bank a year ago, I thought Maple Grove bridge felt slightly threatening and closed-in, with various activities obviously having taken place under its side arches - a marked contrast to the manicured elegance in the photos from 1966 and earlier.
I set aside a momentary twinge of regret that the tunnel mouth isn't fully visible from the top of the bridge, because I guess that those of us for whom this is an emotional resurgence of a well-loved railway feature have to remember that our nostalgic enjoyment of the Two Tunnels project is not its paramount purpose!

Mark A said...

@Blockbell: please could you drop a line to the contact email address on the Two Tunnels web site?

@Dan Gallo: in early March the project plan indicated autumn 2011 as a completion date. When the current contract is done, there *will* be a bit of a hiatus, but the continuation of the construction phase is very much a going concern.

stanley mayer said...

Hi Mark and Frank.
I was down at the devonshire tunnel
today just in time to see hope a clay packing up.
They have done a great job ,I all so stud on maple garden bridge and looked over to the tunnel and the sun was passing over the tunnel it looked absolutely great
a master pice in it's own rights.
hope and clay were telling me the brick work is soled you won't move that by hand.seeing it today like that made me feel good . all the best to you all