Check out what's happening on Clifton Hill

High-grade wire mesh is being draped over an unstable cliff face on Clifton Hill in a bid to reduce the risk of rocks falling onto the road below.

The work is part of a multimillion-dollar project to reduce the geotechnical risks along the critical Sumner to Lyttelton road corridor.

It began a couple of months ago with teams of abseilers using crowbars and airbags to leverage loose rock from the cliff face. Now they are anchoring mesh to the top of the cliff and unfurling it. The mesh will be bolted deep into the cliff at strategic points to form a protective barrier.

The mesh will be left unfastened at the bottom so it can channel any smaller rocks that might fall into the small moat or ‘catch ditch’ at the toe of the cliff.

Christchurch City Council Senior Geotechnical Engineer Dr Ian Wright said the main purpose of the mesh was to slow the momentum of any rocks that might fall from the cliff.

“You want to restrain the rock before it gets any momentum – you want to it hold back into the rock mass,’’ said Dr Wright.

“The mesh will either retain the material into the cliff face or, if it drops, act as an attenuator. It will attenuate the energy and makes sure the rock drops under the mesh rather than bouncing out into the road.’’

Dr Wright said any rocks that did fall from the cliff face would collect in the catch ditch, which would have a concrete barrier around it to provide another layer of protection between the cliff face and the road way.

Currently the road is protected by ballasted shipping containers. Those containers will be removed once this work is completed.