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Making the railway safe after the tunnel collapse at Gerrards Cross
July and August 2005

This page follows earlier pages which you can reach from a link at the bottom of this one.

After peace descended on the Tesco tunnel site on July 10, there was no visible activity until July 21 when the site burst into life.  This page has to be different from other pages in the 'Collapse' group because there is no continuous story to portray, no sequence of dramatic events to illustrate although there has been drama, more a wide range of activities.  But there has been a common purpose, which has been to bring the railway back into use.  This seems to have involved two types of work - removing fill material obstructing the railway on the one hand and removing the load from the tunnel top on the other.  This last also creates conditions suitable for thorough and detailed examination of the remaining structure.  Note that making the railway safe is not necessarily the same thing as declaring the site safe for further development.

This page will begin with a picture of the site on Sunday August 7, four weeks after the last picture in the 'Clearance' page.  It is taken from the same position as that photograph and close to the vantage point for the very first picture in 'meadwaypark.co.uk/Collapse', which is itself now inaccessible.

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The collapse gap is now much bigger than it was.  Five or six segments on both the south and north sides were demolished on the evening of  July 27 - there is a picture later. Up to that point the railway formation had been kept fairly clear but it was covered again with fill material after more sections of rail were cut out and stacked in the tunnel.
The shape of both sides of the collapse site has changed several times but the present situation is that a retaining wall has been built on the south side and one is in the process of being built on the north side.  Most of the wall consists of RSJs about 40 feet long sunk into drilled holes with concrete fill at the lower end and old sleepers slotted between them.  The south wall had been completed before the additional tunnel segment demolition took place which is why there are some concrete pieces at the western end.  When the walls are in place fill material can be cleared from both the railway and the tunnel segment bases.  A roadway has been created on both sides behind the wall.
The other major activity has been the removal of fill from the top of the tunnel.  This began before the end of 'meadwaypark.co.uk/Collapseclearance' so that segments could be removed, but since then the whole tunnel top has been cleared, leaving carefully sculpted sides rising each side of the cleared area.  There are several pictures of the clearance work and associated engineering changes.  Much of the fill material was transported to the station car park but some was taken to a local landfill site and some from the car park has since gone to landfill.  A small amount has been stockpiled on site - small is a relative term!

Removing fill material obstructing the railway.

After the initial clearance was complete, the ground each side of the collapse site was unstable and liable to foul the railway formation.  It also covered the tunnel segment foundations.  The solution has been to build deep fences each side of the collapse site to hold back fill material and allow clearance of the space in between.

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A wet and muddy scene on the south side of the collapse with some RSJs sunk deep in the ground in the foreground, the drill making another hole with most of its screw in the ground behind.









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The fence is far from straight and requires some athleticism to work on.  The sleepers are being inserted and the ground cleared away..














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The southern fence is now substantial and beginning to hold back material.  The material at the far end of the fence and down to the railway did not slip there, it was deliberately placed.  See later pictures.

















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The southern fence is complete, although it has some concrete sections at its western end.  The fill material has been contoured to leave the tunnel segment foundations clear and to give a reasonable slope down to the railway formation.

The northern fence is well under way with most of the RSJs in position.










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A wide view showing most of the railway formation reasonably clear of fill material.  In the centre of the picture is an insignificant hole underneath a section of the signal cable channel.  The next day, a man was working in the hole which must have been at least 5 feet deep.  I understand that contractors Jackson have been attending to the drainage system while the railway is closed as it is in, I am informed, poor condition.  Perhaps that was the reason for the hole.






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Careful contouring of the north side is now in hand.  The excavator is clearing both the tunnel segment bases and the slope to the railway formation
On this north side the tunnel segment bases have not yet been cleaned up whereas on the south side the groove has been cleared of the concrete grout used to secure the tunnel segments in the groove. .









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The RSJs in the north wall seem longer than the ones on the south, and are certainly much closer together, there being only half a sleeper slotted between each.


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Unloading RSJs did not always go according to plan!













Removing the load from the crown of the tunnel segments.


The small section of tunnel at the east end of the development had very little fill on it at any time and that was removed at an early stage.
The western section was cleared from the east and within the Tesco shed framework at the same time.

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Clearance of fill material from the top of the eastern segments of the western tunnel (keep up!).  It was removed layer by layer.  The sculpted sides of the clearance are beginning to emerge.  At this stage the careful clearance to the top of the stitching beam had not been completed.
This work would continue until the Tesco shed frame stopped any more progress.










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It is tricky work inside the Tesco shed frame because of limited headroom.  Note the white framework behind the excavation and that its foundations have been left exposed.

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The framework has been dismantled.  It did not affect the roof structure which still spans from left to right.  There is space for a swimming pool in the excavated area, almost Olympic size.









At about this time, it seems to have been decided that some of the remaining tunnel segments were a bit doubtful and ought to be removed.  The heavy gang were called in.

Makesafe2553 The condemned segments were not lifted out by crane but smashed up by a demolition team.  Several segments are already on the ground and another is being attacked.  In the earlier section of this page it was noted that the railway had once again been covered with fill material, and protection from this event was the reason.

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After much pushing and shoving, and snapping of the reinforcing steel strands, the machine picked up around 20 tons of debris.  It was passed from one machine to the next further up the hill to be dumped for breaking up.

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The demolition team were working at around 8 pm, so light for photography was in short supply.

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Two vehicle cross Packhorse Road, with the help of temporary acting traffic controllers, on their way to the station car park with excavated fill material for adding to the stockpile.  It is not often that a vehicle of the size of the 6 x 6 dump truck is seen on the public highway.

Finally the whole of the top is clear.

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You can see all the way to Marsham Lane bridge in the background with the heavy steel work installed to hold up the western frontage of the Tesco shed in the foreground.  The stitching beam which connects the tunnel segments is clearly visible over the whole length.  It is about a foot deep so that is the amount of scalpings left on the crown of the tunnel, increasing with distance from the crown.

Perhaps it is worth mentioning with the stitching beam visible is that its task is to connect the side-by-side tunnel segments, not to hold the north and south sets together.















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A view not seen for many months - looking through Packhorse Road bridge from Marsham Lane bridge with the foreshortened station car park lights on the right and the protective fence along the unloading siding in the middle.

The vertical white steel beams are at the western end of the Tesco shed structure, being supported by the temporary steel beams.

Bull Lane bridge is in the distance..













The 'Collapse' page serves as the focus for all the events since the tunnel collapse on June 30 and you may return to it here.