Client name: Winstone Aggregates Limited 

Scope of work: KiwiRail Fill Platform (Wiri North Quarry) 

Duration: February 2011 – April 2012 

Location: Auckland, New Zealand

Coffey provided a cost-effective redevelopment model to transform an existing quarry into land suitable for industrial and commercial use.

Evaluating the potential risks and value in rehabilitating a quarry

The Wiri North Quarry, located about 25km south west of Auckland, had been heavily mined since the 1980s and was close to exhaustion. 

Our client wanted to explore land rehabilitation options for future developments of medium to heavy industry and trade retail outlets. A portion of the quarry had already been acquired for the construction of KiwiRail’s new electric train (EMU) depot building, and formed part of the land area assessed as part of this project. 

Sections of the quarry had already closed. Our client urgently sought to understand the potential risks and value associated with restoring this land for alternative use. 

The site was characterised by variable soil and rock fill material overlying basalt basement rock. There was an inherent uncertainty in the ground profile and material parameters, creating settlement and stability risk. The building platform had to be delivered ‘fit for purpose’.

Advanced numerical modelling and specialist laboratory testing to assess ground condition

We provided our client with a design solution to profitably repurpose the closed portions of the quarry. This solution involved the replacement of 600,000m3 of uncontrolled non-engineered fill reinstated to earthworks specifications. We ensured that development costs would be low and the impact on the surrounding environment was taken into consideration.

Our solution gave Winstone Aggregates confidence that repurposing their land would increase its value and provide commercial return.

To avoid the risk of failing settlement and stability criteria, we carried out an engineering analysis, advanced numerical modelling and specialist laboratory testing to assess and define the ground beneath the building platform.

Using this data, we executed key design recommendations through a construction and monitoring program. This included the installation of underfill drainage, the placement of engineered fill and pre-loading to induce consolidation of pre-existing fill materials.

Cost-effective redevelopment model improving land value, reducing geotechnical risk and minimising environmental impact

Our design solutions provided a successful model to improve land value, reduce geotechnical risk and minimise environmental impact, making redevelopment a feasible option to pursue. It paved the way for Winstone Aggregates to progress their plans to redevelop for industrial and commercial use with confidence.

The design contribution to the EMU Depot has played a key role in managing the rolling stock of the newly electrified Auckland commuter rail system.