Ground and slope investigation of A83, Scotland

Project summary

Working with Transport Scotland and its technical advisers, AtkinsRéalis WSP Joint Venture (AWJV), Structural Soils has delivered detailed ground investigations on a stretch of the A83 at the Rest and Be Thankful, which has been the site of a number of landslides. The findings from the investigations will inform the design of Transport Scotland’s Long-Term Solution (LTS), a 1.4 km debris flow shelter, which will increase the resilience of this vital trunk road.

The background

While there is a long history of hillside instability at the A83 Rest and Be Thankful, landslides have increased in frequency and severity in recent years due to the increase in frequency of heavy, intense and prolonged periods of rainfall. The increase in the frequency of incidents means there is a need for a long-term solution to be developed to allow the area to prosper, and the Scottish Government is committed to delivering an infrastructure solution to address the landslip risk in the area.

The A83 trunk road is a vital trunk road connecting the Central Belt of Scotland with Argyll and Bute, and closures can have a significant impact on journeys in the region. The ground investigation work, procured through a Transport Scotland Framework Agreement, was required to inform the design of the Long-Term Solution, which will increase the resilience of the trunk road.

Multidisciplinary approach

Additional RSK companies supporting the work include CAN (rope access teams and specialist hillside borehole capabilities), RSK Geosciences (temporary works designs and coordination), Central Alliance (specialist slope climbing plant and operators, as well as remote monitoring systems), Envirolab (testing capabilities), Drilling Supplies (equipment and materials for drilling operations), Deans Civil Engineering (specialist carriageway reinstatement services), ADAS (ecology and archaeology support), RSK Geophysics (geophysical surveys) and RSK Safeground (utility avoidance and service control).

Operating under Structural Soils’ Framework Agreement with Transport Scotland, the project management team pulled internal RSK resources from multiple divisions and locations throughout the UK to complete the scope of works. Utilising RSK’s comprehensive network of businesses and expertise, Structural Soils was able to internalise all field-based programmed operations, delivering a uniform high standard of safety, provision of specialist plant and technical acuteness that is unmatched in the UK market by a single group.

The challenges

Owing to the location of the project site, there were logistical and technical challenges of maintaining vital public access and use of the road, while using the same road as the means of accessing the slopes above, below and through the carriageway to record data. In order to ensure safety for the workforce and road users, careful coordination was required with the operating company, BEAR Scotland, on-site. Traffic was diverted onto the Old Military Road on a number of days during the summer to facilitate the use of a large crane to allow ground investigations to take place on the slopes above the carriageway. These temporary diversions were communicated to the public and stakeholders by Transport Scotland via news releases and its social media outlets and stakeholder email updates issued by BEAR Scotland.

Innovation and the ability to overcome a host of physical, practical and logistical factors made access to many of the exploratory positions very difficult and unsuited to conventional investigation plant or access methods. Specialist personnel were necessary to complete the scheduled works and, because of the dynamic nature of the site, required adoption of a flexible approach with adaptable methods to fit specific conditions.

The solutions

To overcome the unique challenges of the project, multiple specialist ground investigation techniques were employed on steep slopes to obtain the detailed ground information required for the design of the Long-Term Solution.

To achieve this, the team deployed a specialist project team of over 50 members to execute the work. The techniques required included sonic drilling of boreholes through the carriageway, drilling of boreholes on steep and irregular slopes above and below the carriageway and geophysics investigations on sloped ground. Collaboration with the client, Transport Scotland; the technical advisers, AtkinsRéalis WSP Joint Venture; and industry experts was key to successfully and safely completing the ground investigations. Structural Soils drilled angled boreholes on slopes of up to 60 degrees, situated as far as 60 m from the carriageway, to depths of 35m.

The impact

When completed, the A83 Rest and Be Thankful Long-Term Solution debris flow shelter will increase the resilience of the A83 trunk road and provide protection against landslides, debris flow and boulder fall, ensuring Argyll and Bute remains open for business.

Through a collaborative approach with the client, Transport Scotland, and its technical advisers, AtkinsRéalis WSP Joint Venture, Structural Soils developed a highly positive working relationship that resulted in a successful project. Innovative solutions to problems not previously faced on UK land-based ground investigations were an essential element to being able to complete the scope on what is an extremely challenging site.