Remedial action is being taken on a section of the M74 extension where workmen have carried out THREE separate repairs since it opened last summer.
Road bosses have dismissed a series of partial collapses as "normal", but the Evening Times can reveal that liquid cement grout could be used to try to halt "snagging" across both carriageways.
We reported last week that a dip had formed along a 20ft section of the fast lane on the westbound carriageway. Within 72 hours of our article the partial collapse had been repaired.
We can now reveal that a section of the motorway began to sink within weeks of the official launch of the extension, which cost £445million to build.
Officials at Transport Scotland have admitted there was a partial collapse of all three lanes on the eastbound route, just yards from a slip road that takes drivers from Polmadie on to the motorway at J1A and directly beneath a gantry displaying a sign for J2 Rutherglen/ Cambuslang.
The fault was repaired two months after the extension opened – but repairs had to be carried out a second time on exactly the same spot weeks later.
A Transport Scotland spokeswoman said: "Localised settlement close to the Polmadie junction appeared shortly after opening the road. The area affected is about six metres long and extends across the road from the eastbound slow lane to the westbound fast lane.
"This is not an unusual occurrence in any road and often occurs where a services track crosses the road – for example BT cable ducts or a water duct. The normal course of action is to allow the settlement to stabilise over time and then effect a repair."
However, the first repair to the eastbound carriageway was made last August – even though the motorway opened only weeks before, on June 28.
That was not enough to stop it and the spokeswoman admitted: "Further inspection showed the settlement had continued, so a second repair was carried out in November."
But she said the fault did not end there. Instead, it spread directly across into the fast lane of the westbound carriageway, which had to be repaired last Thursday.
This latest semi-collapse triggered detailed inspections by engineers of the affected area about six weeks ago. They said that part of the motorway was sinking into "soft ground" beneath, according to Transport Scotland.
The spokeswoman said: "The most recent inspections have shown soft ground under the area of settlement, which the contractor will permanently repair by injecting grout into the ground."
The extension was built by a consortium of some of Britain's biggest construction and civil engineering groups.
Known as the Interlink M74 Joint Venture, it comprised Balfour Beattie, Morrison Construction and Sir Robert McAlpine, as well as infrastructure specialists Morgan Est.
Last week the consortium claimed it had been gagged by Transport Scotland from commenting to the Evening Times.
This week the roads agency cleared the way for the consortium to speak to the Evening Times about the problem, only to reveal no one really knows what is causing the fault.
A consortium spokeswoman insisted an investigation was continuing to identify the fault and that grouting was an "option" being considered, although no final decision had been taken.
She said: "Interlink M74 Joint Venture is aware that the road surface has settled over a small area of the M74 just to the south of Junction 1a at Polmadie.
"The problem is confined to a localised section, which is being resurfaced as necessary while ground investigation works are being carried out and analysed.
"A permanent solution will be undertaken when the cause is fully assessed and the appropriate measures identified."
"Interlink is committed to undertaking this work as soon as possible with minimal disruption to people using the road. Meanwhile, precautionary advisory messages have been displayed by Traffic Scotland to assist drivers."
Despite the investigations, Ainslie McLaughlin, director of major transport infrastructure projects at Transport Scotland, said any suggestion that the agency had launched a major inquiry would be "a distortion".
He shrugged off the controversy and said: "All new roads, like new houses, require an element of 'snagging' – and that is precisely the case in this instance.
"The M74 is already bringing significant benefits to Glasgow and the wider Scottish economy and will continue to do so for many years to come."
Mr McLaughlin claimed the defect was "isolated."
However, Transport Scotland is refusing to divulge whether other road repairs have been carried out on the M74 extension.
It said the Evening Times would have to submit a Freedom of Information request – but it was likely to be refused on the grounds of cost.