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The Sapperton Railway Tunnel, named after the nearby village of Sapperton (near Cirencester, Gloucestershire) carries the Golden Valley Line from Stroud to Swindon through the Cotswold escarpment. It was begun by the Cheltenham and Great Western Union railway in 1839 and taken over by the Great Western Railway in 1843, being completed in 1845. There are actually two tunnels, the main one at 1 mile 104 yards (1704m) in length,〔 to 〕 and separated by a short gap, a second at just 353 yards (323m).〔 to 〕 ==Construction, engineering, and maintenance difficulties== The initial plans for the tunnel, dating from 1835, were unusual in that it was proposed to construct the tunnel on a curve, but this seems to have been abandoned before any construction was done; some works remain which are thought to relate to the approach route for the original line, but no excavations were made on that line for the tunnel itself. In 1836 "Mr Brunel" was appointed as engineer for the project;〔 this refers to Isambard, but the involvement of "Mark (sic) Brunel" is also recorded.〔 Brunel promised to get rid of the "objectionable" curve, and plans of the revised straight alignment were deposited in 1838. Preliminary shafts were dug, the work beginning in 1837, to ascertain the geological conditions, on the same straight alignment on which the tunnel was eventually built. In 1841 work began on four additional shafts of a larger diameter, quoted as 3 or 6 metres by different sources, plus a trial heading along the tunnel alignment. The line was opened in 1845. It was found that the intended route passed through a layer of fuller's earth, which was not sufficiently stable to allow construction of a tunnel. The plans were therefore revised to situate the tunnel in more stable strata at a shallower depth, at the expense of steeper gradients on the approaches. This also reduced the length of the tunnel and so reduced construction costs; it has been asserted that this was the actual reason for the change to the shallower depth, rather than simply an effect of it, but the geological cross-section shows clearly that the header, on the originally-proposed deeper level, passes through a much greater length of fuller's earth than the tunnel as built, and also makes it clear that information gained from digging the shafts would have made it apparent that this would be the case.〔(【引用サイトリンク】title=The Approaches to Sapperton Railway Tunnels )〕〔 This diagram also casts doubt on the unsupported assertions which are sometimes made〔(【引用サイトリンク】title=The Cheltenham Flyer ) 〕〔(【引用サイトリンク】title=Diesel multiple unit, 1950s )〕 that the gap between the two tunnels is the result of a roof collapse in the early days of the tunnel. This gap coincides precisely with the level section at the summit of the line, and also with a dip in the contours of the ground above which brings the ground level below the depth at which the transition from tunnel to cutting is made at the outer ends of the tunnels. It is unlikely that a chance collapse would have taken place to correspond with these features with such convenient precision. The gap is also shown to be in the more stable oolitic strata rather than the unstable stretches of fuller's earth which are more liable to collapse. The lateral alignment of the revised tunnel route was the same as the planned deeper route, and this left the ten exploratory shafts intersecting the tunnel and continuing as pits up to 6 metres deep below the tunnel floor. The pits were capped with timber to support the track and ballast. However, no records were left as to whether or not the pits had been filled in. In 1950 a train driver noticed a void beneath the tracks and it became apparent that work was required to stabilise the pits. The original timbers were removed and the pits spanned with prefabricated concrete beams reinforced with bullhead rail and shear links. One more beam was fabricated than was required for the work and this was stored in a nearby yard. Again it was not recorded whether the pits were filled. In November 2000, heavy flooding caused the collapse of one of the capped shafts. Emergency work over a period of four weeks was carried out to stabilise the collapsed shaft and similar preventative work was carried out on some of the other shafts; the four larger shafts, however, were left untouched. An erroneous report attributes the damage to the collapse of the canal tunnel running underneath;〔(【引用サイトリンク】title=Chaos over as rail track is reopened )〕 in reality the canal tunnel is to the north of the rail tunnel and does not pass underneath it. In 2001 it was decided to test the redundant beam remaining from the 1950 operations to destruction in order to determine its strength, as part of surveys intended to discover whether the route would support the loadings required for a route availability index of 8. It was found that the concrete had deteriorated and would not support the loads required for an index of more than 5. Further stabilisation was therefore required as a matter of urgency. The operation was carried out under a complete possession over a period of seven days by over 100 people working 12-hour shifts, many of whom were accommodated in temporary buildings at the site. Road-rail plant was used, standing on one track of the double-track tunnel to remove the other track and replace the beams underneath. The 1950 beams were cut into three sections using a diamond-tipped saw blade to facilitate removal. Each pit was then spanned with new prefabricated beams, one main support beam under each rail plus additional spacer beams to fill the gap between them. The new beams were fabricated in three sections to avoid exceeding the working load of the plant, which were joined once the beams were in place using stainless steel bolts. After work on the one track was completed, the road-rail plant was put into road mode and driven onto the new beams from where it could work on the other track. Not until the old beams were removed did it become known that the pits had indeed been backfilled in the course of earlier work and the fears of falling into a six-metre hole were unfounded. The seven-day possession did not give enough time to fully stabilise all four large shafts. Priority was given to the two least stable ones and the work on those was completed, but the remaining two were only partially stabilised, the beams under the up line being replaced but those under the down line being left alone. A further operation was scheduled for Easter 2002 to perform these final replacements.〔(【引用サイトリンク】title=The Rail Engineer - Featured Articles )〕〔(【引用サイトリンク】title=Network Rail Media Centre - Victorian Shafts at Sapperton Get Strengthened )〕〔(【引用サイトリンク】title=Sapperton Tunnel, Gloucestershire, UK )〕 A roof collapse occurred in October 2009, necessitating the closure of the line for relining work.〔(【引用サイトリンク】title=Swindon to Kemble Railway )〕〔(【引用サイトリンク】title=Rail Travel Disruption Monday 26th to Friday 30th October )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sapperton Railway Tunnel」の詳細全文を読む スポンサード リンク
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