Rail disruption in Ayrshire is expected to last well into the summer.
A sinkhole at Gatehead had closed the line between Kilmarnock and Barassie after being discovered at the start of June.
Repair work was expected to last until early July but ScotRail's website now states that a replacement bus service will be in place until Sunday, July 17.
Network Rail Scotland has been working closely with the Coal Authority on the sinkhole, which experts say is complex because of the mining legacy in the area.
In a video showing ongoing work at the site, one of Network Rail's geotechnical asset managers says a solution to the issue is currently being devised.
The expert said: "Since June 4 we've been working closely with the Coal Authority undertaking ground investigation in the form of boreholes.
"This is to investigate for the presence of any potential voiding beneath the railway.
"The purpose of the investigation is to gather information so that we can design a remedial solution that'll enable the track to reopen in a safe manner.
"The local area has a rich mining legacy and at this specific location there are recorded mine-workings and mine shafts in the vicinity.
"It's complex task to investigate these features , and we need to make sure that we are satisfied that we can run trains safely over this specific location and the surrounding areas."
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