The Rest and Be Thankful road is expected to remain shut for three weeks as it undergoes repairs to landslip damage.
Around 6000 tonnes of debris fell on the A83 route amid heavy rain nine days ago and it has been closed ever since.
Road management and maintenance organisation BEAR Scotland said the carriageway has been undermined after material was washed away from beneath the road and embankment.
Teams plan to work round the clock to build a concrete wall to support the road and a culvert to carry water under it.
A new temporary catch-pit will be created and the cliff formed below the road reinforced with concrete.
BEAR said the repairs could take up to three weeks before one lane of the road can safely reopen under traffic light control.
The landslide also blocked a parallel alternative route on the Old Military Road, which reopened later in the week.
It has since shut several times overnight amid heavy rain forecasts and will again shut overnight on Thursday.
Eddie Ross, BEAR Scotland’s north west representative said: “We’ve concluded designs to allow us to safely repair the A83 following last week’s landslip.
“The repairs involve complex engineering methods which involve stabilising the recently formed steep channels on the embankments above and below the carriageway, as well as repairing the road which was heavily damaged by the landslip.
“A catch-pit will also be installed to help provide additional mitigation for the A83.
“With good weather and no unforeseen circumstances we expect these repairs will take up to three weeks to complete, and our teams will work 24 hours a day to get the repairs completed as quickly as we can to allow the A83 to safely reopen.”
He added: “With weather warnings for thunderstorms in place overnight across much of the country we have taken the difficult decision to close the local diversion route again from 9pm due to the restrictions in being able to safely monitor the hillside.”
A diversion is in place from 9pm via the A83, A82, A85 and A819
STV News is now on WhatsApp
Get all the latest news from around the countryFollow STV News
Follow STV News on WhatsApp
Scan the QR code on your mobile device for all the latest news from around the country