The stabilisation of two new highway cuttings as part of a substantial trunk road widening scheme. The Glandyfi site is restricted on one side by the estuary and the railway and on the other by a steep, wooded hillside.
The first cutting measured 15m high by 420m long and the second 12m high by 200m long, both formed through unstable slate/mudstone bedrock.
Design required the installation of 800 double corrosion protection (DCP) monobar anchors, with working loads up to 650kN and lengths of 11m. Extensive multi-cycle suitability and acceptance anchor testing was required in accordance with BS8081.
5500m² of sprayed concrete facing was applied with two layers of heavy gauge weldmesh reinforcement amounting to 3000m³ of concrete in total. This also included the installation of a backwall drainage system.
With working at height and on narrow benches cut into the hillside different approaches had to be taken across the site, using a combination of drill masts mounted on 8T tracked excavators, a bespoke telehandler basket and compact tracked drill rig.
Three different drill systems were required to cope with the varying ground conditions and hole diameters; these were down-the-hole (DTH), drifter and cased drilling.
Duration: 1 year +
Client: Carillion Civil Engineering
Location: A470, close to Aberystwyth, Wales