A major north road will remain closed all weekend amid fears boulders could rain down on motorists.
And helicopters may have to be used to ferry workers and materials up steep rock faces to make a stretch of the A82 safe.
The main route between the Highland capital and Fort William had to be closed after two giant boulders crashed on to the carriageway – leaving drivers facing a 120-mile detour.
Work to reopen the Loch Ness stretch of the road was described last night as “technically challenging and a major undertaking” by Forestry Commission Scotland.
The two boulders, each weighing about six tonnes, came loose above the road between Invermoriston and Balbeag.
It is thought they were dislodged after an oak tree fell further up the slope and landed on a boulder field, triggering a landslip.
Engineers from roads company Bear Scotland and a FCS geo-technical team will continue to work on the road over the weekend.
A helicopter may have to be brought in to help airlift materials and equipment to the top of the cliff to make it safe from further rock falls.
The two boulders which triggered the closure will be broken up over the weekend and catch fencing will be put in place to protect the road.
An FCS spokesman said last night it was hoped the work would be completed on Sunday night or on Monday morning.
The Forestry Commission is carrying out a major project to improve the embankments along the length of the A82 – dubbed the Steep Ground Harvesting programme.
The rockfall area has not been worked on and was not due for development until September.
Project manager, Alex McLeod, said: “Together with Geo-rope, our technical advisers, we are co-ordinating efforts to clear debris, assess and make safe the hillside, and we will continue to work with our colleagues in Bear Scotland and Police Scotland to complete the necessary work as quickly as possible.”
Iain McDonald, Bear Scotland’s north-west unit network manager, said: “We continue to work with Forestry Commission Scotland to enable the A82 to be reopened following the rock fall on Thursday and although the road is now clear of debris, there are still concerns about the slope.
“Public safety remains the ultimate concern and we are therefore advising that the A82 remains closed as operations progress.”
However, campaign group the A82 Partnership questioned the effectiveness of the work.
Spokesman Stewart MacLean said: “Major closures because of these rock falls were not a feature until the Forestry Commission started their work.
“I know they have said it’s a project lasting between 10-15 years to improve safety but in the short term it’s having a major impact on the road and doesn’t seem to have made it any safer.
“It could easily have resulted in major injuries or even death when you see the size of the rocks.”
Mr McLeod added: “We are looking into what underlying causes may be behind this incident but it illustrates once again the urgency behind our long-term programme.
“Felling the mature trees along the A82 and cleaning and scaling the rock face will significantly reduce the likelihood of these types of incidents in the future.
“We’d like to thank all local residents and road users for their continued patience and understanding.”
Northbound drivers have been diverted along the A86 from Spean Bridge before following the A9 to Inverness and then back along the A82 towards Loch Ness if necessary.