Sleepyhead Estates

Ohinewai, Waikato

Project Detail

This project involves the construction of a 10-hectare warehouse and factory building on liquefiable sands and highly compressible peat. A wider, mixed-use commercial, retail, and residential community is also proposed on an adjoining 180ha block of land. The development includes:

  • A 100,000 m² factory and warehouse for Sleepyhead
  • A rail siding to the Sleepyhead site, off the North Island Main Trunk railway
  • 660,000 m²of light industrial and industrial development on adjoining land
  • 85,000 m² of commercial development including mixed retail outlets, convenience stores and petrol stations
  • 33,000 m² of residential development for 1,100 new homes
  • 600,000 m² of public open space

Significant ground improvement will be required to address widespread liquefaction risk and settlement issues due to soft ground and peat. Approximately 1,000,000 m3 of new fill will need to be imported to the site to lift the land above flood levels and to provide a suitable bearing layer for support of new buildings.

Estimated Project Value: $100M (Stage 1 only)

Initia's involvement

Our involvement in this project has comprised the following:

  • Multiple stages of geotechnical investigations
  • Liquefaction and lateral spread assessment
  • Design of ground improvement solutions for mitigating liquefaction susceptibility
  • Specifying and managing Dynamic Compaction field trials
  • Design of preloading to address settlement
    (up to 500 mm combined settlement)
  • Specification of instrumentation and monitoring for preload trials
  • Preparation of Expert Evidence for the proposed Plan Change Hearing and Resource Consent Application
Geotechnical risks and mitigation
RISKS MITIGATION
Liquefaction susceptibility
The site is underlain by loose Taupo Pumice Alluvium sands which are highly susceptible to liquefaction under seismic events. Ground improvements are required to prepare the land for development.
 Initia assessed several different ground improvement options and assisted with costing these to support feasibility assessments for the development.
Dynamic compaction was selected as the preferred ground improvement/treatment method. A field trial was conducted to determine the efficacy of dynamic compaction using a 90t crawler crane with a 13t weight. Pre-trial and post-trial testing was undertaken using seismic CPTs. The post-trial tests confirmed effective densification to 5 m below ground level and analyses demonstrated that liquefaction susceptibility was effectively mitigated over the same depth range. It is proposed to employ this method over the wider site.

 
Earthworks – Fill importation for lifting site levels
Up to 1 M m3 of new fill is required to lift the Sleepyhead Estates site above flood levels and to achieve design grades for construction of future buildings.
 Earthworks specialists from Initia conducted a regional investigation of suitable fill sources.
Several quarries and other borrow-sites were visited and the geotechnical properties of the materials were tested and assessed and tested. The team from Initia was instrumental in identifying a source of quarry overburden material which is to be imported to the site at highly competitive rates. The material can also be hauled during winter months and used for preloading purposes. This has resulted in a significant reduction in both cost and programme.

Client Referee
David Gaze, Director, Gaze Property Ltd

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