Client: C.J O’Shea
Project start: September 2008
Project finish: May 2009
Location: Millharbour, London
J Browne were awarded this contract by main contractor, C J O’Shea, who needed to divert an existing 1600mm diameter sewer, to enable the commercial development of apartments they were constructing for developer, Galliard Homes, to proceed as planned.
The work involved a 240m pipe-jack with three lateral connections, two end connections and associated manholes. It was originally intended to construct a new 1800mm diameter sewer to take the flow from the existing 1600mm diameter sewer but due to difficulties with the ground conditions it was agreed with the client and asset owner, Thames Water, that the new sewer could be reduced to 1500mm diameter.
A closed face micro tunnelling machine, capable of coping with the challenging ground conditions, was used to form the new sewer line. A 12m x 8m shaft, 6m deep, from which to launch the tunnelling machine, was excavated, together with two 6m x 4m reception pits, also 6m deep.
J Browne were selected for this complex project as a result of previous work carried out for main contractor, C J O’Shea, their wastewater expertise as Thames Water’s largest wastewater repairs and maintenance contractor and due to their existing civils framework agreement with fibre optic network owner, Geo Metro.
The excavation for the launch pit was particularly challenging as the area was heavily congested with existing services. Also, ground water was encountered in the shaft at approximately 6m, so a 6” pump was required to continuously pump water out of the excavation.
A 10T gantry crane was installed at the base of the launch shaft to facilitate the movement of equipment and materials to and from the tunnel.
In addition to the tunnelling work, there was 30m of open cut excavation, construction of a number of new manholes and connections to existing manholes.
An additional element of the project was to transfer several existing fibre optic cables from the original sewer to the new sewer.