The complex project is required to bypass a 130 meter stretch of mains sewer under Mancunian Way after the network was damaged when a sinkhole opened up in August.
The ground is considered too unstable to conduct the work from one side of the carriageway and UU has already built on concrete shaft in order to stabilise the ground around the sinkhole.
The project will involve the construction of another two shafts, one at the top of Manor Street and the other further along the eastbound carriageway of Mancunian Way.
A tunnel would then be used to link up the shafts with a new concrete pipe. The old stretch of sewer would be stabilised and abandoned.
UU wastewater network manager Tony Griffiths said: “Our damaged sewer is six foot wide, more than 40 foot deep, and serves thousands of properties in the city centre.
“Unfortunately, the geological conditions in the area are very unstable and dangerous. It would have been impossible to carry out a traditional repair and keep the road open throughout.
“The tunnel scheme we’re proposing is major engineering – the type of work that would normally take 12 months to plan – but we are fast-tracking it to get both sides of the road reopened as quickly as possible.”
UU has been working with Manchester City Council (MCC) to stabilise the immediate area and assess the extent of the damage to the sewer and the road structure.
MCC executive member for the environment Cllr Kate Chappell said: “Engineers working for UU have discovered that the situation beneath the Mancunian Way is more challenging than anyone had originally anticipated.
“This is clearly a huge piece of engineering work, of a nature that would normally require months of planning, and will sadly mean that the Mancunian Way will remain partially closed for longer.”
A version of this story first appeared on wwtonline.