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Friday, 26 March 2010

Looks like this was some sort of transport system

Devonshire Tunnel portal excavation
The end of another working week. You'll see that Hope and Clay have been carefully plugging away to excavate the earth from in front of the structure. Their method has been to remove the load on the structure in an 'even handed' way, monitoring for movement as they go - tunnel portals can be sensitive, in that they sit at a junction between made ground and undisturbed material. Hence, they reward being treated appropriately.

The fill is now gone from the portal down to the level of the trackbed. Monitoring will now continue, as movement, if any, is likely to be gradual and occur over weeks in terms of time - and hopefully less than a smidge in extent. The portal, having shrugged off heavy vibration from passing trains for over ninety years, is not likely to be seriously troublesome. (There are several accounts from people who lived above this particular tunnel that mantlepiece ornaments had to be glued down ...)

Devonshire Tunnel portal excavation
The cylindrical structure is the access shaft built when the tunnel was sealed. At a later stage the original access was tending to bury itself, and the shaft had a bit of an extension added to its top - if you've visited the cutting you'll remember this, around four feet high and buried in brambles. The contractors have tidily removed the extension - they swiped it off in one piece with a bucket - Matt happened to be there at the time. After removing the extension they've put a new cover on the access shaft.

Devonshire Tunnel portal excavation
Both shaft and block wall stays put for the moment, as it's not yet a good time of year to alter the environment for the (very few if any) bats inside. Another aspect of the task is that topsoil and subsoil are treated separately, subsoil can then be reused where appropriate in the excavation and later covered with topsoil in which things will grow. The images show that some of the cutting sides are already dressed with topsoil - the final part of their treatment involves grassing them over, but the topsoil itself will also contain seeds from previous years growth and will provide continuity.

This unveiling is a bit like a birthday present for the project, after four years of anticipation. It's a present which is pretty well unwrapped now, but for the time being it's not easy to see and very much a work in progress - looking from the direction of Maple Grove bridge, the spoil heap's in the way.

There was a concern that they may have been damaged, but it looks as though the tunnel portal's wing walls - at either side - are going to be fine - the photos show a glimpse of the up side wall capped by its coping stones. Unlike our three other portals, this one seems to be 'As built'.

Lined up against the other architecture the city can provide, this structure is inconsequential. However, many of us find that it feels particularly good to have it back.


stan mayer said...

Nice one Mark it's good to see thing moving along a bit .
It should be ok when all uncovered
hope and clay seem to have it all in hand.I think we all new that there may be some sort of a problem
unearthing the tunnel it's been covered a long time but fingers crossed

all the best mark keep safe.

raven said...

Fantastic photos,
is it my eyes or does the small digger bucket on the left appear to be floating in the air??

raven said...

Happy Birthday Mark, and the Two Tunnels Group.

A great start to a great project!

Blockbell said...

Unwrapping a present indeed - well said - and it feels just great to have it back.