http://www.bbc.co.uk/news/uk-england-manchester-34447899A new sewer needs to be dug under one of Manchester's busiest roads as part of repairs on two holes which have opened in two months.
United Utilities said it has to close an existing badly-damaged sewer and create a new 130m stretch of plastic sewer piping on Mancunian Way.
Manchester City Council said it is trying to minimise the disruption.
The second hole opened last month near to work fixing a road collapse caused by heavy rainfall in August.
Tony Phillips, area manager for United Utilities, said it hoped to repair the sewer but had found the damage was greater than expected.
He also said that the geological problems had added to the company's difficulties.
Mr Phillips said sealing off the old sewer - built in the 1920s - digging the first new tunnel in Manchester for many years and installing plastic piping had doubled the repair bill to £4m.
"It is not just a significant piece of civil engineering, it is also a significant cost," he added.
Councillor Kate Chappell (Labour), who is responsible for highways on Manchester City Council, said: "It is going to take until the New Year but the most important thing for ourselves and United Utilities is to make sure it is going to be the fix for the next generation."
She said the work would create disruption during the run-up to Christmas but she added the council was delaying some roadworks until the New Year and has brought other works forward to open new routes.
Repairs to the first hole, which was 15ft (4.5m), were being carried out by United Utilities and Manchester City Council.