As Auckland faces continued pressure on its land resources, more difficult sites are being developed in an effort to contain urban sprawl. This means developers now have the problem of overcoming unstable ground conditions caused by the often clay and silty soils in the region. These conditions occur when ground water is trapped above an impermeable clay or rock layer and creates a ‘slip plane.’
Shear-key construction is a cost-effective and environmentally sustainable solution for hillside sites with unstable ground conditions. It works by excavating a ‘key’ into the hillside, draining the slip plane by tunnelling / trenching techniques, and constructing a compacted earth key at the base of the slope. This engineers an in-ground retaining solution that prevents further slippage of the ground above, and readies the site for development.
Dempsey Wood’s successful application of difficult shear-key construction techniques is regarded by many in the industry as ‘best in practice’.
‘Dempsey Wood completed the 80,000m3 bulk [and shear key] earthworks operation and the associated land drainage
within one earthworks season and despite the relatively challenging ground conditions, they showed throughout the works a high level
of competency and judgement which facilitated a smooth and efficient construction operation.’
P B C Bosselmann, Principal Geotechnical Engineer
Foundation Engineering Consultants Ltd.