Orewa North, Auckland, New Zealand
Background
Grand Drive is a multi-staged, terraced residential subdivision located in Orewa North, Auckland.
The subdivision is the vision of client Orewa Subdivision Limited, primarily owned by Cabra, who purchased the land, previously a sheep and beef farm, at least a decade before construction began.
The subdivision comprised three stages with a combined total of 117 residential lots of at least 450m2 each. The development included substantial earthworks to provide the terraced finished land form, a range of retaining structures and subdivision infrastructure including roads, access-ways and a permanent pond.
Scope
The landform showed clear evidence of deep, historic, deep seated land sliding.
Our scope incorporated supplementary geotechnical investigations, development of the ground model and design work to stabilise the land form. We were also required to work with the project team to provide an appropriate, stabilised landform that met with the projects’ economic demands.
Geotechnical design included a 150m long palisade wall at the toe of the subdivision. Several large reinforced concrete walls were constructed in a top-down fashion, being installed as palisade walls initially and then being exposed and faced with mesh and shotcrete. Designs also included some 70 timber retaining walls which were constructed within a tight schedule to meet construction programmes.
Construction monitoring and certification of the works were also key features of our work scope.
Findings/Challenges
The complex geology of the site and the 50m change in elevation across the site provided demanding conditions for the design and construction of the subdivision. Having a large quantity of high quality investigation data made design of the remedial works possible despite the steep topology and development intensity required. Good communication between the client, CMW civil engineers and the contractors made the construction process smooth, helped to keep costs down and maintained good progress on site.