Client: Bear Scotland

The A83 is a major road in the south of Argyll and Bute in the Scottish Highlands. It runs from Tarbet, on the western shore of Loch Lomond, where it splits from the A82 to Campbeltown at the southern end of the Kintyre peninsula.

A section of the A83 near Furnace has a sea wall constructed to protect the road from tidal movement. However, a partial collapse of the wall allowed water to migrate into the pavement sub-base and wash out fill. The voiding led to surface fractures and notable sinking in the road surface. Immediate action was required to remediate the voiding and stabilise the sub-base. The wall also needed reconstruction to prevent future issues. 

A visual inspection was carried out in March 2019, which identified the carriageway defects. They included large cracks on the uplink/shore side and half-width of the uplink carriageway. 

The cracks were severe, over 25m in length and depth of 250mm; in some areas, the cracks measured 30mm width.

More recently, a 25m long crack formed 400mm from the top of the wall. Furthermore, bulges and holes had appeared in the sea wall. The original construction was founded on Puddle Clay tidal/storm action which caused further erosion at the base of the wall. 

 

Alternatives

The standard option for this kind of project is closure, with excavation and reconstitution of the fill. However, the closure of the A83 was not an option. The road is the only convenient route into Furnace and the surrounding villages, closure would mean a diversion of over one hour for business and residents in the area. A fast solution that could that did not require a closure was essential.

 

Geobear solution

The client initially considered a temporary repair by clearing stone from the front of the wall and placing formwork in front of the holes. Afterwhich the voids could be filled using foam concrete or expanding geopolymer. 

However, using Geobear geopolymer material, we could provide a permanent solution. Our geopolymer can fill voids and stabilise the sub-base before a surface repair. The geopolymer material a water sealant that would prevent future erosion of the fill. 

The methodology of the Geobear solution also meant that one lane of the road could remain open at all times; this would ensure a traffic diversion was not necessary. 

Using GPR surveys, Geobear could accurately identify where the voiding was and create a treatment plan to ensure the stabilisation of the road. The area of treatment was 48m3; our engineering team designed a pattern of works that would require geopolymer material injected into the voiding from the road surface. The material was pumped in at a depth of 1.5m through 14mm steel tubes.

The material we used is a two-component expansive geopolymer; on entry to the void, the two components react, and when mixed, this creates the expansive force to fill the voids. The material also acts as a water seal; as a supplementary aspect of the works, we sealed the sea wall joints to prevent access to burrowing animals in the critical areas. 

For this project and other emergency works, Geobear prides itself on response times. We received the instruction at 15:50 on a Friday and our teams were on-site delivering the works on the following Tuesday morning. We were able to complete the works in 3 days, and the road has subsequently handed to Bear Scotland.