Gerrards Cross Tesco tunnel construction
Background
and progress 1999 to 2008
Tesco won Planning
Permission, after Appeal, to construct a store in the middle of
Gerrards Cross, Buckinghamshire, England. It is being built
over the infilled railway cutting that was first excavated for the
Great Western and Great Central Joint Committee in 1905/07. The
process features the erection of pre-fabricated tunnel segments over
the railway with infill material brought in by train.
Progress was dramatically halted on the evening of 30 June 2005 when part
of the tunnel structure collapsed on to the line underneath, miraculously
without a train being involved. The story of the recovery from the
collapse is told at this link
The story starts in 1999 when preliminary drillings took place all over
the area involved but I have photographs from 1988 which provide a good then-and-now
comparison.
Looking from Marsham Lane bridge towards Packhorse Road Bridge and the
station, these pictures tell the whole story. In 1988, the fast through
lines had been disused for several years and the platform roads had already
been slewed for greater speed through the station. None of this is
visible today from the same vantage point. What we do see is the two
sections of the tunnel, the gap where the collapse took place and the framework
for the Tesco store.
Not only did the Tesco project make changes to the station area but before
that the layout was simplified. By the start of the project in 1999,
the semaphore signals had gone together with the signalbox, and the Up line
had been slewed to join what had been the Down through line, leaving just
two tracks through the station. These changes made for a much faster layout
which suited the increasing number of Chiltern Railways trains running through
non-stop and also provided more car parking space.
But the presence of the Tesco project is also apparent in the 2008 view.
In the distance, the turn-back siding added, with its associated crossover,
at the same time as the other track changes, has been extended to form a
siding for trains bringing in 1000 tonnes of fill material. The conveyor
belt system to bring the fill material to the site is on the right of the
car park, and the cutting has lost a lot of trees. All the space behind
the Up platform has been raised to form an entrance to the Tesco site from
Station Approach and to provide working space, entirely covering the garden
that had been created on the site of the old Up platform line and the Up
platform.
To put these two collages in place, here is a plan of the Tesco site.
We have been looking west from, first, Marsham Lane and then from Packhorse
Road.
In 1999 there was exploratory drilling going on all over the site, including
the area to be used for the infill siding.
These pictures contrast the scene from Bull Lane bridge. There
had been a siding here in the early days of the railway so the ground was
likely to be suitable. The 2005 scene shows a train of 1000 tonnes
of scalpings, topped and tailed by the usual Class 66 locos, although 60s,
59s and 47s were seen.
The trains were a tight
fit in the extended turn-back siding. They were unloaded by a grab
onto the track used by the grabs, and transferred by the other grab from
the track to the conveyor belt hopper - in this picture the latter grab is
in the distance but not working as evidenced by the empty conveyor belt. Two
trains a day was the usual level of activity. Next is a view of an
arriving train snaking over the crossover and into the siding. The trailing
loco was usually being dragged without any crew.
Click on the thumbnails to see larger images.
Now we can turn to the tunnel contruction project, starting with
1999 - 2008 contrast.
The 1999 drilling site is now entirely under the tunnel structure. The
bricks on the left are part of Packhorse Road Bridge (PHRB) which are still
there in the 2008 view but lost in the darkness of the tunnel. The
concrete structure is at the same height as the arch springing shown in 1999
and supports the tunnel segments which are in place under PHRB. The
brick piers are still there but their structural strength has been taken over
by the foundation works that support the aforementioned concrete structures.
Hard to see, but very preliminary works have started on the left through
PHRB, including drilling in a number of places. The 2008 scene shows
the Tesco site work area on the left and the tunnel as so far completed,
complete with its gap. The tunnel segments under PHRB are apparent as
are the huge concrete supports. If and when the project is completed,
only the tunnel portal, somewhat nearer to the platform ends, will be visible,
PHRB being totally lost to view.
Tunnel construction started in 2004 with the creation of bases for the
tunnel segments.
A very large crawler crane was delivered and assembled, here waiting for
the first tunnel segments to be delivered. The continuous base for
the segments is to the left of the crane.
This is October 2004 and the first segments have been placed overnight,
with the next batch lying on the ground close to the crane. This was
Sunday 10 October and the contractors had a Possession for the whole day.
Many of the segments have now been placed by the crane into the waiting
grooves to the north and south of the railway and the pairs pressed together
at the crown. Each segment weighs about 22 tonnes and is a metre wide. At
this stage very little fill material had been placed.
Looking from PHRB, fill material is being placed on the north side and
some is being shifted by this temporary conveyor to the south side.
On a snowy day, work continues, but now there is sufficient support for
the sides of the tunnel arches to allow larger quantities to be moved from
north to south. The structure in the foreground will form the stitching beam
that attaches each segment to its neighbour on the same side.
Later in February, much more fill can be moved.
The segments are covered in waterproof layers. Here the tunnel is
quite close to Marsham Lane and the huge crane has gone, to be replaced by
a smaller one later.
The final southside tunnel bases are being built on the deep piled foundations.
A smaller crane is now lifting the last few segments into place near Marsham
Lane in the early hours of the morning.
Almost the last segment to be placed is eased into position at around
3 a.m. on 9 June 2005.
Finally, some of the last pictures I took before the collapse with people
going about their day by day work. Three of them taken on 21 June 2005
and the last, of the Tesco store frame, just 26 hours before the disaster.
I have put them together as a collage.
To return to the home page on the Tesco Tunnel project, click here.
Text and pictures, © Guy Gorton 2008
