The slip road was closed on 28 June after significant subsidence created a 700mm deep hole in the carriageway. Other nearby areas that had been patched as recently as May were also found to have subsided. Since then, Transport Scotland’s operating company BEAR Scotland has engaged specialist contractors to carry out investigations including ground radar and topographical surveys.
BEAR Scotland has also been working with the Coal Authority, as records show historical mine workings close to where the subsidence occurred.
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The Coal Authority is now mobilising on site and will commence drilling a series of boreholes over the next two to three weeks. These will provide further data on any voids below the surface, which areas are safe to work from and inform any necessary future work.
Intermittent lane closures on the M80 northbound carriageway will be required during off-peak hours to allow works traffic to exit the site. These are not expected to cause any significant delays.
In parallel, BEAR Scotland is investigating the feasibility of constructing a temporary link road around the affected area so that access to Pirnhall Roundabout can be reopened while remedial works are completed.
A Coal Authority spokesperson said: "If the cause of this incident is found to be related to historical mining then we will work with BEAR Scotland to return the site to normal as soon as possible. It is important that we fully understand the make-up of the ground before this can be determined and this can take time, so we apologise in advance for any inconvenience caused."
