Page 11 - SISK NEWS JANUARY 2017

Tunnel Vision

In 1873 Sir John Hawkshaw’s vision for a grand new railway tunnel began construction. The
Severn Tunnel links South Gloucestershire in the west of England, to Monmouthshire in south
Wales under the estuary of the River Severn.

The Severn Tunnel Welsh portal in 1886 when it was completed. For well over 100 years it was the longest mainline Railway tunnel in the UK

The Welsh portal is four miles and 624 yards from 130 years later Sisk Rail, along with our contractor
the Gloucestershire entrance, and of this distance Vertex, were tasked to carry out vegetation clearance
two and a quarter miles are underneath the and masonry repairs on the approach to the tunnel
River Severn. The total length, including approaches, is on the Welsh side. This coincided with a six week
approximately seven miles. period when trains were stopped from running to allow
installation of the new electrification equipment.
Whilst it remains a great feat of civil engineering,
there were many setbacks during its construction. In Originally it was a small order to remover 370m3
1879 miners working uphill on the Welsh side struck of vegetation, as well as some masonry repairs and
the Great Spring. This poured fresh water into the unblocking of seven weep holes over an eight day
tunnel from an underground reservoir and within a few period. However, once we began work in October,
hours the tunnel was flooded to a depth of 150 feet in Network Rail decided that all the vegetation required
the air shafts. It poured in at a rate of 6,000 gallons a removal which equated to 15,500m3. As we only had
minute, 23 million gallons a day. It was eventually cut 10 days left on the blockade we therefore had to work
off using shields and many pumps were used to drain 24 hrs a day to achieve this using roped access teams.
the water out. This required us to mobilise all available operatives to
assist in clearing the vegetation, with up to 17 abseilers
The works were completed in 1886 when the first at a time clearing the banks.
passenger service ran.

Sisk News | January 2017 11