AN INVESTIGATION into mysterious cracks in the newest stretch of Greater Manchester's motorway ring road is to result in a series of closures.

Now six miles of the £220m `missing link' section of the M60 around Oldham is to close for the next six weekends while Highways Agency engineers try to find the cause.

The cracks, which are not connected to flooding in the same part of the ring road which cost £4.6m to put right three years ago, were spotted more than 18 months ago.

Digging

So far engineers have studied the cracks and filled them in but the probe will now involve digging a trench across the whole carriageway.

Work will start at 9pm on Friday night and finish at 5am on Monday between junctions 19 at Middleton and 23 at Ashton under Lyne.

The agency believes work will be completed by August, weather permitting.

One side of the motorway will be closed with a contra-flow on the opposite carriageways while the work is being carried out.

Various entry and exit slip roads will also need to be closed.

A 40mph speed limit will be in place throughout the roadworks.

Matthew Sweeting, agency operations manager, said: "We don't know why the cracks have started appearing.

"They are quite small cracks and pose absolutely no danger to drivers and until now, we have been fixing them as they appear. But they shouldn't be there so early in the life of the motorway and it has got to the stage where we decided to have a full investigation."

Overhead message signs will be used to advise drivers of the closures so they can choose an alternative route.

The Highways Agency will deploy extra crews for the duration of the work with a dedicated patrol to cover the roadworks area and react to any breakdowns or accidents to help keep drivers on the move.

Incidents and traffic conditions will also be monitored from motorway cameras.

The nature of the work required will only be known once the investigations are completed.

Mr Sweeting added: "It might turn out not to be that serious and we can simply carry on mending them as they appear," he said.

"But if remedial works are needed, closing the motorway at that point is not an option. It is not the busiest section of the motorway but it is very busy. There would have to be some form of traffic management while the work was done."

When the flooding problem was discovered, investigations showed the road builders were not at fault and in 2006 the agency paid to alter the camber to allow surface water to drain away easily and an `interceptor' tank was built beneath carriageway to collect excess rainfall.

£4.6m bid to stop M60 floods