WAIMAKARIRI BLUFFS ROCKFALL MITIGATION

PROJECT DESCRIPTION

Waimakariri Bluff lies on the side of the SH73 State Highway which links Christchurch to the West Coast of New Zealand. These rock slopes are highly fractured and active with countless frittering rocks which would regularly fall on to the road surface. This created a significant hazard to road users as well as the highway maintenance team who were removing rock debris regularly.

NZTA wanted to address this hazard by installing a mesh netting/drapery that would control the displacement of any future rock falls. WSP were engaged to design a solution for the rock fall risk.

WSP visited the site to investigate and evaluate the topography and the size of rocks that could be of risk, this formed the basis of the design. Ensuing this, Geofabrics provided technical information about various Maccaferri mesh systems.

The tender was awarded to Abseil Access, a specialist geotechnical drilling and abseiling contractor. During the tender process, Abseil Access requested that Geofabrics modify the product and extend the vertical attachment ropes to aid an easier installation.

OUR SOLUTION

The final design required 34 rolls (2,400m2 ) of Maccaferri Steelgrid HR. This is a simple netting/drapery mesh solution, anchored over the crest and covering the entire slope. Each rock is guided down the slope under the mesh and contained at the toe of the mountain.

Geofabrics NZ utilised Maccaferri MACRO software to select the mesh type and estimate anchor loadings based on the slope height, geometry and estimated debris volume.

PRODUCT USED

Maccaferri® Steel Grid® HR Rockfall Netting

• High, strength, high stiffness steel composite netting system for rockfall mitigation and slope consolidation works
• Available in a range of system tensile strengths ranging from 50kN/m up to 180kN/m to allow projects to be cost and technically optimised
• High strength at low strain and high punch resistance at low deformation (high stiffness)
• Different levels of coating protection for durability; wires and ropes are coated with Galmac® galvanising to Class A level and can be additionally coated with a thermally bonded layer of PVC for more aggressive coastal road environments
• Reduces the stress on the mesh by its ability to transmit loads directly to the top anchors
• Less maintenance costs as it does not unravel if wire breakage were to occur