18 Jan 2010
The existing 25” cast iron rising main carries sewage from the south side of the city of York to Yorkshire Water’s sewage treatment works at Naburn, some three miles to the south of the city. A risk of leakage was found in a section of the pipeline where it passes directly under the main A64 dual carriageway.
Yorkshire Water’s framework partner, Costain Ltd. was main contractor on the project to replace approximately 140 mtrs of the rising main. Open cut techniques were only feasible on 30 metres either side of the A64, for the remaining 80 metre section of the pipeline, Costain needed a trenchless solution for the pipe replacement as the main A64 could not be disrupted. An additional complication was the presence of rare tansy beetles. The York area contains some of the only suitable habitat left for tansy beetles.
Costain called us in to recommend a solution and, after examining the site and the ground conditions, our engineers recommended unguided auger boring. Other solutions were considered, including directional drilling but were ruled out due to the ground being too sandy. Unguided auger boring was agreed as the least risk solution to minimise ground disturbance where the new pipe was to pass under the A64.
Costain prepared the launch and recovery pits prior to us setting up on site. In a ten day window we installed 80 metres of 914mm lost steel casing in 12 metre sections. The host pipe was then sliplined with a 600mm ID ductile iron sleeve, which was attached to a towing head and pulled back through the pipe by the auger rig as the auger flights were removed.
After installation and pressure testing, Costain connected the new section of pipe to the rest of the open cut pumping main and the sewer was returned to service.
The existing 25” cast iron rising main carries sew...
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