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Report - Sapperton Canal Tunnel, Gloucestershire - PART1 (Daneway Portal) - February 2015

Discussion in 'Underground Sites' started by Bertie Bollockbrains, Mar 6, 2015.

  1. Bertie Bollockbrains

    Bertie Bollockbrains 28DL Regular User
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    INTRODUCTION:

    Sapperton Tunnel, through which the Thames and Severn Canal flows, is 2.17 miles long and is the UK’s third longest canal tunnel. The tunnel burrows under part of the Cotswold Hills and at its deepest point is 65m below ground. The tunnel was completed on 20th April 1789 and at that time was the longest tunnel ever dug in England. It has been disused since the 1920s at least. The Thames & Severn Canal, as its name implies, formed a link between the two rivers.

    This explore was done in 2 parts and is listed as two reports, as each tunnel portal was done on a different day using completely different methods.

    This report is on the Daneway Portal end, which was done a relatively deep wade. Visited with Huey and a non-member.


    HISTORY:

    All photos in this section plagiarised from the interwebby thingy

    Sapperton Tunnel on the Thames & Severn Canal is the third longest canal tunnel in the United Kingdom at 2.17 miles. The nominal width is 4.4m with a minimum height of 4.7m. The roof can be significantly higher in parts of the unlined sections, due to the amount of rock that fell during construction blasting operations.

    The first boat passed through the tunnel on 20 April 1789. The last commercial passage was in 1911, by a boat captained by Mr Walter Pearce from Chalford. As early as 1916, roof falls made the tunnel impassable to normal boat traffic. Today Sapperton Tunnel remains impassable with a number of significant roof falls, and a complete blockage near the Daneway end.

    Tunnel Longitudinal Section
    The graphic below shows a longitudinal section of the tunnel. The profile of the ground level above has been derived using Ordnance Survey mapping data. The scale of the vertical axis is 7 times that of the horizontal to provide a more meaningful profile. The vertical lines represent approximate positions of tunnel construction shafts. Some of these are referred to as Air Shafts on OS maps. The two sections of the tunnel shaded red denote unstable rock formations (Fuller's Earth), and these sections are fully lined with brick or stone. The blocks of black shading within the tunnel denote areas of known wall and roof falls, with a total blockage near the Daneway end.

    [​IMG]

    Tunnel Entrances (Portals)
    Probably the most architecturally significant structure on the Thames & Severn canal is the Coates Portal. The mainly neo-classical structure was in a very poor state of repair in the early 1970s. Fortunately, the Cotswold Canals Trust raised the funding for restoration, and it was officially 're-opened' in 1977.

    [​IMG]

    Daneway Portal, built in the Gothic style, was also in a very poor state of repair with most of the battlements lying in the bed of the canal. In 1996 the Canal Trust again raised the funding to have the portal restored.

    [​IMG]

    Inside the Tunnel
    As can be seen from the photo below, there is no towpath in the tunnel.

    [​IMG]

    To get a boat though the tunnel, one or two men would lie on their backs on board the boat and 'walk' along the tunnel wall or roof. This process was known as 'legging'. Another method used a pole to push the boat along, again using the tunnel wall or roof.

    Distance Markers
    The distance through the tunnel is recorded on 'chain' marker plates fixed to the wall. The distance between plates is one chain, an old English measurement for 22 yards (20.3m). The markers start at 0 at the Coates Portal and reach to 170ish at the Daneway Portal.

    [​IMG]

    Roof and Side Wall Falls
    As might be expected after over a century of being abandoned and unmaintained, sections of tunnel wall and roof have collapsed. Areas worst affected by falls are marked on the tunnel graphic above, and these are predominantly in sections of Fuller's Earth.

    [​IMG]

    [​IMG]

    Tunnel Construction

    Tunnel construction started in late 1783 and was completed in 1789. The work involved several different contractors. Work began by setting-out the tunnel route on the ground. A number of vertical shafts were then dug along the route to the required depth. The shafts were about 2.4m in diameter and it is recorded that 26 were sunk in all. The depth of these varied from about 60m to less than 10m. The approximate locations are shown on the tunnel section graphic above. One of the shafts was abandoned before reaching the required depth, probably due to flooding.

    From the base of each shaft, a 'heading' (small tunnel about 1.2m wide and 1.8m high) was cut in two directions - along the tunnel line. Headings were also cut in from what would become the tunnel entrances. Once headings had been connected, and the alignment checked, the tunnel was excavated to its full size, and lined with brick or stone where required.

    The photo below show an open shaft:

    [​IMG]

    Problems after Construction

    Issues of poor workmanship were recorded during construction. One of these was where only one ring of brick was used in sections of the 'long arching' (see tunnel graphic), where three was specified. Fuller's Earth, being a clay, has the property of expanding when wet. This is not a good situation within the tunnel, as this had a tendency to put extreme pressure on the brick and stone structure, resulting in significant distortions of the side walls and roof, and eventual collapse.

    Rain water percolating down through the ground gives rise to a number of springs inside the tunnel. Springs have, however, been the cause of problems throughout the tunnel's history. These occur when water forces its way up through the clay lining in the canal bed. When the spring later dries-up, after periods of low rainfall, water from the canal then drains down through the bed via the same route. One solution, as late as 1904, was to line vulnerable parts of the tunnel with concrete, and provide spouts for the springs to discharge into the canal above the water line, as shown in the photo below.

    [​IMG]

    THE EXPLORE

    This report is on the Daneway Portal, visited with Huey and a non-member.

    With water no more than about a metre deep, it was a rather enjoyable pleasant wade, except for the idiot who turned without waders because he thought the water was only going to be about 4 inches deep. He came out shivering. Err that was me I confess. With the complete blockage at the Daneway End, there was only about 200m of tunnel to explore.

    First view looking in:
    [​IMG]

    and looking out:
    [​IMG]

    A chain marker, showing 170 chains from the Coates Portal (about 2 miles)
    [​IMG]

    Bulging walls show that this tunnel is very unstable:
    [​IMG]

    The first roof-fall
    [​IMG]

    The view in from top of the roof-fall...look how clear that water is! I may have to bring the wife swimming here in the summer.
    [​IMG]

    Triple brick construction...
    [​IMG]

    and that is a far as we got, as the next roof-fall completely blocks the tunnel, time to head out...
    [​IMG]

    [​IMG]

    SUMMARY

    The plan was to then drive round to the more exciting end of Sapperton Tunnel - Coates Portal - and then canoe to the roof falls in the centre of the tunnel about 1 mile in. Unfortunately there was no way to fit a canoe in. Fortunately I had saw an alternative way in at the Coates Portal, but that required different equipment and was left to another day.

    PART 2 of this report will be published soon, it is me snorkeling and swimming a mile into the tunnel from the Coates Portal. Not really a clever thing to do in the first week of March but hey ho they don't call me Mr Bollockbrains for no reason.

    Thanks for looking.
     

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  2. Lenston

    Lenston Bajo Tierra
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    Quality stuff there mate and looks very interesting, looking forward to the second part :D
     
  3. wellingtonian

    wellingtonian Subterráneo
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    Good stuff mate, can't wait for part 2 :D
     
  4. ACID- REFLUX

    ACID- REFLUX 28DL Regular User
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    Nice ones matey :thumb

    You can deffo" see where the water comes through the Limestone :)Pity about the Kitty litter though.

    Roll on part 2
     
  5. Garou Garou

    Garou Garou 28DL Regular User
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    Great place that. I've got almost identical photos to yours, but nice ones taken at night of the portal.
     
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