A83 slip recovery work ongoing

The catch pit shows engineers fixing metal mesh to the slope using soil nails to stabilise the sides before excavating the pit. The pit will have a capacity of around 1000m3.

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Essential work to make safe the area of hillside that slipped and blocked the A83 earlier this year (January 29) is forging ahead.

Taking care to maintain social distancing and to observe all current NHS and government health advice, a team of experts has been carrying out extensive operations to stabilise the slope and construct a back-up catch-pit.

Engineers are working to repair the damage to the forest road at the head of the slip. The short, 5m trench (the darker area centred on the front of the machine) is the line of the piling that will be installed to strengthen and underpin the road. The first 10 piles are being drilled into this trench. A total of 50 metres of road is to be stabilised.

Led by Forestry and Land Scotland, the team includes the geotechnical engineers and consultants involved in resilience works elsewhere on the Rest and Be Thankful, and partners Transport Scotland and BEAR.

FLS Planning Manager, John Hair, said: ‘We’re channelling a lot of resources into this and are working on it seven days a week to make this area safe.

‘Over 1,000 tonnes of debris landed on the road back in January. It took a lot of clearing up but that loss of material from the hillside presented other problems as well. We’re currently underpinning a 50-metre stretch of the forest road to strengthen it and prevent any further major collapse.

‘The landslip channel has been stabilised but, in the event of future extreme weather events potentially affecting this part of the slope, we are constructing a catch pit that aims to prevent debris from reaching the road surface.

‘Traffic management will be in place for approximately a further two weeks to allow us to complete the catch pit. We will be working on stabilising the forest road for another four weeks after that but will not require any more traffic management.’

Currently only one lane of the carriageway is in use.

The area of hillside affected is land that FLS looks after but is well away both from those areas that have slipped in the past and from areas where previous mitigation work has been carried out.

Engineering assessments indicate that the incident was the result of exceptionally heavy rain causing a section of hillside above the forest road to slump and block a drainage culvert. This resulted in water damming up, overflowing the forest road and reaching the downhill slope, carrying surface material downhill and also creating a channel for more water to travel down at a faster rate.

John, added: ‘This event arose from a very particular set of circumstances that are unlikely to apply to other sites and situations. However, aware as we are of the increasing occurrence of prolonged spells of heavy rain, we have already reviewed and adapted our inspection process to include checks on other forest roads set in similar landscapes.

‘We are also developing climate change adaptation actions to make the forests and land more resilient and mitigate such risks.’