A 1960s sewer which runs alongside the main Bristol to London railway line has been repaired using no dig technology. The ageing asbestos concrete (AC) sewer, operated by Wessex Water, had suffered a number of fractures and was relined using a cure in place pipe (CIPP) to safeguard it for the future.
The work involved inserting a preformed polyester lining saturated with resin and specialist additives to provide the finished liner with greater strain capacity. The liner was inserted with low 'head' and cured in place using hot water.
Wessex Water engineer Barry Burtenshaw said repairing the 375mm diameter sewer in Corsham, Wiltshire, using a no dig method had many advantages.
He said:
“Without the use of this technology it would have been impossible to repair the sewer without closing this busy section of railway line which would have been extremely disruptive and costly.
“In addition, it meant that we could safely make improvements to support the pipe’s structure without the risk of compromising the asbestos cement pipe’s integrity.”
Ring fractures a common problem for AC sewers
CCTV investigation of the sewer revealed that it had lost structural strength due to decalcification and sections expose to the elements had caused exfoliation of the outside surface leading to a number of ring fractures, which are a common problem for AC sewers.
Before the relining work took place the sewer was cleaned using a Weirdermann 1000 Recycler, which has over 400m of reach and is one of the quietest machines of its kind in the country. Wessex Water chose to use the Weirdermann 1000 Recycler to minimise disruption to residents in the area.
Once the cleaning was complete the sewer was relined in two shots using liners measuring 325m and 323m.
Mr Burtenshaw added:
“These were unusually long liners for us to fit in one of the only sewers in our region located next to a railway line.”
“As an additional safety precaution most of the work was completed at night when very few trains use the Bristol to London line.”
The sewer was built in the 1960s next to the railway line, which runs in a ‘cut in’ six to 10m below properties in the area. Thes unusual location was chosen to avoid the need for a tunnel more than 600m long through the land adjacent to the railway line.
The work was undertaken by Wessex Water contractors Onsite. With its new liner installed the sewer is now expected to continue providing a safe, reliable service for more than 50 years.
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