Drainage is always a critical element when constructing a new housing development and the landowner must understand the water course under the land to plan the evacuation of excess water. The project managers of a new housing estate in Barnstaple, Devon, UK identified that the capacity of a 600 mm diameter concrete culvert on the site was not sufficient to prevent flooding.
The client commissioned OnSite Central Ltd, a specialist contractor for water and waste management, to plan and carry out all the works associated with a culvert expansion. The culvert runs under the only access road to the building site which had to remain operational at all times and a trenchless solution was therefore required. Nathan Hand, Project Manager, appointed Genseed Underground Services Ltd, a specialist contractor, to develop a solution.
The existing concrete pipe was to be replaced by a new 750 mm diameter twin wall pipe. The usual method for upsizing pipes is pipe bursting, where an expander is pulled through the existing pipe, splitting it and forcing it open with the replacement pipe pulled in behind. On this occasion, however, the limited depth of cover and proximity of other services meant bursting the pipe outwards could cause damage and surface heave on the road.
What is believed to be a new, previously untried method was devised specifically to overcome this issue and that was to encapsulate the existing concrete pipe with a 930 mm diameter open ended steel pipe; breaking up the concrete pipe on the inside during the installation ready for the new pipe. This was achieved using a TRACTO GRUNDORAM pipe rammer from a launch pit constructed by OnSite. To complete the work Genseed designed and manufactured a multi-function custom built cutting, splitting and crushing head with internal blades that fractured the concrete pipe during the ram.
A total length of 21 m of culvert was upsized prior to the installation of 750 mm diameter twin wall pipe and grouting, which was completed by OnSite.
Accuracy in this particular application was essential particularly given the close proximity of high-pressure gas and water mains. Jamie Marshall undertook the precision installation saying: “The GRUNDORAM is exceptionally reliable and accurate which is important when there are other services to avoid underground. Our custom-made blades incorporated a guiding system to ensure the steel tube remained concentric to the concrete culvert and we set the pipe ramming guide rails to the line and grade of the culvert lowering the encapsulating head on to the them. We then butt- welded sections of steel tube to the back of the head and a winch cable was pulled through the culvert and attached to the head with the GRUNDORAM attached to the rear. After connecting an airline, the ram started and carefully progressed in sections until the encapsulating head was successfully exposed in the receiving pit where it was cut off and removed ready for the twin wall pipe.”
The whole job took just over two weeks from start to finish, with full rectification completed by the Onsite team. Nathan was impressed by the final result, commenting: “This was an example of great teamwork. From the initial call to TRACTO UK, that recommended Genseed to us, to the development of a bespoke solution for the culvert expansion and the works completed by all the teams, we completed the job with no interruption to site traffic, no damage to other services and no damage to the road surface. The client was very pleased with the speed and smooth delivery of the project.”