The Great Western Railway opened the Chipping Sodbury Tunnel in 1902 but, unfortunately, the tunnel cuts through a major Cotswold aquifer and flooding has been a serious, if intermittent, problem throughout the tunnel’s lifetime, with an inflow as high of 2.5m³ per second once recorded during particularly violent spring rainfall. The original drain proved entirely inadequate to cope with these quantities and flooding well over track level has been witnessed in the tunnel itself and in the cuttings as recently as 1999 and 2002.
A hundred years of sporadic disruption and closure to a section of this important rail artery had led Network Rail to invest £3 million into a new drainage system, with the advantages of such outweighing the cost and difficulty of the work, as well as the inevitable rail closures during construction.
A feasibility study was conducted through specialist hydrologists and tunnelling designers Haswell, and it presented a number of options for the new drainage system design. After considering many potential solutions, plans were eventually agreed for a conventional gravity drainage system involving the installation of around 6.5km of pipeline from the east cutting, through the tunnel and into the outfall in the west cutting.
Edmund Nuttall was appointed to carry out the work and installed Polypipe CGU’s Ridgidrain structured-wall drainage pipe as its preferred solution.