been a lot going on at the Costain/Tesco site in 2009, most of
largely unnoticed by the local population. One important
has been the replacement of the tunnel segments destroyed during
immediately after the collapse on June 30, 2005. Even this
very obvious unless you look over the parapet of Marsham Lane
although the sight of the blue framework of the crane visible
the public car park fence could hardly be ignored.
is an account of the final part of this replacement task, made
by a lot of preliminary ground work and some research and
into the design of the segments. 63 segments were placed,
them half-segments to the original design to square off the ends
original tunnels, 2 half-segments to start and end the sequence
new-design segments, and 59 full size new segments. The
new-design segments are not obviously different from the
but they do have a slightly different profile and the mating of
north and south segments at the crown is different.
used the word "completion" but that only means that there
one tunnel instead of the two we have had since 2005.
There is a
brief account of "what next" at the end of the page.
thumbnail to see a larger image. You can go the TescoTunnel
home page here.
Installing the replacement tunnel segments.
A 250t crawler crane was brought to and assembled at the Costain
site. The segments weigh around 22 tonnes each, but they
be lifted at a considerable radius. Date February 14.
A very large platform was built for the crawler crane, together with a wide access route. Preparations included stabilising the ground underneath, boring some deep piles and safety fences round everything. The crane placement and preparation work are quite different from those employed by the original contractor. You can see both the earlier cranes on other pages of this website. Date February 20.
The first task undertaken by the
to assist the building of this temporary gantry. All this
was, of course, done at night during a Possession. When
as shown in the next picture, the gantry was used to support the
first segment being placed as there was no opposing segment for it
be supported by. Once segments were in place, the crane
longer reach the gantry which had to be dismantled from track
and taken out through the tunnel.
The train, 165018, is heading west into the western part of the tunnel. The eastern, and shorter, part is in the foreground.
In a few more days, trains will be invisible as they were in 2005. Date February 23.
additional structure on
the top, the gantry is ready for
use. Date February 27.
new segments have been
placed. The temporary supporting gantry is now
redundant. This is where your scribe confesses that he fully
intended to get out of bed in the early hours to take some
action photos but regrettably his willpower proved inadequate to
task. Date March 2.
base and the channel for the segments survived the 2005 collapse and
quite good order. After all the rubble, fill material and
covering was removed only a small amount of remedial work was needed
make them fit for use now. The foot of each segment is
retained in position by wooden blocks and wedges which are later
replaced by grouting the gap.
Segments queue for placement.
Date March 4.
side segments are firmly anchored
into their channel. On the right is the lower part of the
platform being used by the crane. Two things are worth
here. Along the right-hand edge of the tunnel bases a rail
will be fixed for a gantry that will straddle the tunnel
the work to be done over the top and down the sides of these
The other thing to note is that the entire tunnel length from here to Packhorse Road bridge to the west, on both south and north sides, will have to be excavated to the level you see here. Whilst a lot of preparatory work has been done, it is not very photo-worthy, but I hope to record some of the action later. Date March 5.
temporary gantry is no longer in
use but has not yet been removed. The space for the
segment shows daylight. Date March 5
Here is the
space from a different angle. The stainless steel face to
opposing segment shows clearly from here. Date March 5.
The next three pictures are of a delivery of yet another segment. Date March 5.
The streak of sunshine on to the track through the tunnel gap will be extinguished permanently in a few days. I hope the passengers in Chiltern 168002 enjoyed it. Date March 6.
the halfway mark in segment
placement. Date March 11.
segments in place and many
Date March 13
small gap left to fill. Date
along the north side. Also
seen is the crane platform at the right, built up in layers on
layers. Date March 20.
the team on the south side is
mixing and placing grout. Date March 20.
Segment placement is almost complete, there being just one half segment to go in at the other end on the left on this picture - the gap is protected by safety fencing. In the foreground, looking west, it is possible to see the slight difference in profile where the new segments meet the old. The stitching beams on the new segments do not stand so high so that the top of the concrete is at the same level as on the old segments. Date April 3.
slight profile change shows here
too. On the right is the base of the crane platform.
ground it stands on is at approximately the level created during
recovery work after the collapse, but hugely reinforced in a
ways. Date April 3.
east towards Marsham Lane Bridge,
the almost completed new work completes the link from Packhorse
bridge to just short of Marsham Lane bridge. Date April 8.
from the north side of the linked
tunnels. Date April 8.
north side complete. Date April
last half-segment waits to be
and fitted in the gap, which we have seen in earlier
between the old western tunnel and the new segments.
Date April 8.
Finally the last segment is in place so the south side is also complete. Date Apr 17.
What next? The old and new tunnel segments seen in this and
other pages will be used as formers for the placement of a
concrete outer casing. The new casing will be the load
bearing structure, not
the precast concrete segments.
You can skip the page about the west portal and go straight to the continuation of the completion of the main structure here..
TescoTunnel home page here.
Pictures and text © Guy Gorton 2009
Updated 8th June 2009
tyo final page added October 2014