Kopu Marine Precinct – DuraForce® & DuraGrid Ground Stabilisation

As one of the Covid 19 Recovery (fast-track Consenting) projects, the Kopu Marine Precinct will provide a boat servicing facility in the Hauraki Gulf region. Targeted to open in May 2024, it will consist of an 80m long commercial wharf and floating pontoon, enabling in-water marine servicing and vessel loading, an expanded haul out area, as well as an upgraded concrete reinforced slipway with a public boat ramp and car park.

The site consists of part of the silt trap running from the original jetty adjacent to the Waihou river toward Thames. Normally dredged out every couple of years, this combination of hard sand and estuarine silt required significant stabilisation to support the new infrastructure.

DESIGN

To reinforce and stabilise a working platform over such soft estuarine silts, DuraForce AS410 was specified across both the hard sand and silt trap areas to separate the aggregate being layered onto the silt surface. DuraGrid X 40/40 was also added to reinforce and stabilise the GAP65 aggregate layer. A further layer of Tenax 3D-T would be placed for pavement stabilisation.

The ground had to be stabilised enough to bear the weight of the large cranes required for construction of the pontoon and jetty. Heavy-weight geotextile was also placed beneath the rock revetment area as new ground was extended into the river

INSTALLATION

Progress was hampered by extreme weather events as well as having to deal with tidal surges. The hard sand areas were aggregated first to provide a firm base for machinery to work from. Once DuraForce AS410 and DuraGrid X 40/40 were placed, the base was supported enough to begin building the carpark pavement with the Tenax 3D-T stabilisation layer.

Construction of the lower levels became extremely difficult during King tides, as water often flooded the entire area. Once built, however, the new Kopu Marine Servicing and Business Precinct will further utilise the area’s proximity to Auckland and the Hauraki Gulf, opening greater possibilities for transport and tourism into the Coromandel region.

The DuraForce and DuraGrid provided the following benefits to the project:

• DuraForce geotextile separates aggregates to prevent fines migrating into the pavement layer.
• DuraGrid geogrid stabilises aggregate layers over very soft subgrades.
• Heavy duty DuraForce geotextile under rock rip rap to prevent erosion of the riverbank.