In about 4-6 weeks time, one of the more interesting parts of the Crossrail project will make a significant move forward as part of the Royal Docks is drained to reveal the top of a Victorian railway tunnel for the first time in nearly 80 years.
This is the Connaught tunnel that was constructed in 1878 to run underneath two major docks — and is currently being repaired and upgraded to carry Crossrail trains. In fact, it is the only vintage tunnel to be reused along the entire length of the line.
The two docks that the railway runs under are linked by a short canal – and it is here that the complex work has to be carried out, as they have found that the roof of the tunnel here is perilously thin. Thus, around the end of March/early April, the canal will be drained and the top of the tunnel cut away once again and a new concrete roof put in its place.
Time to take a wander back to have a look at how things have changed – from above ground only this time.
The western end of the tunnel has been cleared and the base lowered in preparation for the new railway to be lain on top.
At the other end though, the old Silvertown overland station that used to serve when this old tunnel was used by the North London Line has been swept away and the area is also being cleared and new concrete bases laid for the future railway as it runs overland for a short stretch until it ducks down again, to pass under the Thames.
It is however, the bit in the middle that is of most interest – and you can see that highlighted in this (old) map, right in the middle of the two docks.
Here, steel caisson walls have been driven down either side of the tunnel under the docks and will shortly be in-filled to create a solid watertight(ish) wall.
Making it a slightly awkward site to work on, is that a modern road bridge runs right over the site, so they are going to have some modest constraints caused by the lack of head-roof. Also, the caisson walls cut off a pedestrian bridge that crosses the watery gap – so they have built a new floating bridge – which currently at least offers a very close view of the works.
What you won’t see though is the rather nice Victorian brick pumping head building, which has been carefully demolished to make space for a larger replacement. The building will be re-erected probably by the SS Robin further east in the docks.
So, in just a few weeks time, the dock here will be drained away and the roof of that actually quite remarkable Victorian tunnel will be revealed once more. The bit here is in fact not Victorian, but the results of a 1935 modification, and it is that later change that has broken and fractured. In the rest of the tunnel, while wet and dirty, it is structurally intact.