Soil Nail Wall – Dowse to Petone

Fletcher Higgins Joint Venture 2008

Part of the Dowse to Petone Project involved building a new service road at the rear of the buildings that were accessed directly off State Highway 2. The new service road cut into the toe of the hill and required a large retaining wall to be constructed.

Project scope

Griffiths were tasked with constructing the wall from start to finish. Construction of the wall included drilling and testing a sacrificial nail for design purposes, drilling and installing production nails of various lengths, fabrication of nail heads, fixing mesh to the rock face and applying sprayed concrete to the wall.

Due to the unstable nature of the rock locally, a blinding spray was required around the area of the test nail to give a firm and regular surface to place the jacking plate against for the testing of the sacrificial nail. Once the testing was completed work on the production nails was able to commence.

The top rows were accessed by a large scaffold platform which was constructed after the blinding spray. The platform accommodated a portable drilling rig that was lifted into place. The scaffold level was lowered as the nail installation progressed.  The lower rows were drilled from the ground using a multi-angled rig. All holes were drilled with a down hole hammer.

Once the nails were grouted into place, the specially fabricated nail heads were installed and a heavy galvanized steel mesh covering the whole rock face, was attached.

After installation of the mesh and drainage holes, the whole wall was sprayed with 48 cubic metres of shotcrete.