BAM Ritchies

Case Study: A77 Haggstone Soil Nailing

Client: Transport Scotland

Designer: Halcrow

Location: Near Cairnryan, Stranraer

Date: 2008

As part of the construction of a new climbing lane on the A77 north of Cairnryan, BAM Ritchies undertook slope stabilisation by soil nailing. Some 1,450 linear metres of 60 degree slope up to 15 metres high was treated.

The drilling and installation of the soil nails was undertaken as the slope was excavated. Ground conditions consisted of glacial till overlying weathered and competent rock and was relatively free of water.

Prior to drilling and installing the working nails, ten test nails were installed and stressed to confirm the design and installation process.

Following the test nails, approximately 5,000 soil nails with a total length of 20,000 metres were installed by up to six of BAM Ritchies rigs. Drilling was achieved by the use of Down-the-Hole (DTH) hammers and air flush.

The nails comprise grouted in-situ Dywidag GEWI Bar double corrosion protected in a 125mm hole. They vary in length between 2 metres and 16 metres. Grout is neat OPC having a design 28 day strength of 40 N/mm2. It has a water cement ratio of 0.45. Selected nails were tested to 210kN by BAM Ritchies’ engineers to ensure that the specification was being met.

Each nail is fitted with a 400 mm x 400 mm galvanised head plate. The surface facing is Maccaferri’s Macmat®. This was initially secured at the top when the first nails were installed and then unrolled as the work progressed. It was retained and secured by the nail head plates.