ECAN - Huritini Halswell Weed Screen & General Civil Construction

SCOPE:

Environment Canterbury Regional Council needed to replace its existing Weed Screen. Grant Hood Contracting was the successful tender for the construction of the civil works and site preparation.

This project included following items:

• Removal of mussels as per consent request from project area

• Design and installation of piles and connecting points

• Installation of concrete slabs to support the winch system and electrical/control equipment

• Surveying the as-built location of installed piles and slabs

• Installation of rip rap on the riverbed and banks

• Reinstatement of hardstand areas to support site access and operation of the dragline.

The winch and screen were supplied and installed by Vector Lifting (Vector). Vector fabricated the screen to suit the as-built location of piles and slabs. Vector install and commissioned the winch and screen following the completion of the civil works.

Following an extensive flood in 2019 which caused extensive erosion to the Rangitata River bank Grant Hood Contracting guided the river away and undertook further work to avoid potential landfill entering waterways.

A flood event in December 2019 caused erosion of the right bank of the Rangitata River in a number of locations including at the Peel Forest closed landfill located at the end of Dennistoun Road. Some waste from the perimeter of the landfill entered the river and was subsequently cleaned up. There was concern that further erosion of the right bank could result in parts of the main landfill falling into the river.

Grant Hood Contracting was engaged to guide the river away from the landfill with a large sacrificial gravel embankment constructed in front of the terrace on which the landfill is located. The bank is to be approximately 250 m long and 5 m high and will be constructed of river gravel extracted from the central island directly adjacent to the site. 38,000 m3 was used for the construction of the embankment.

During the pre-start process, a bird survey was undertaken before any machinery movements or earthworks were begun. Site Fencing was set up to protect the public from accessing the work area.

The first step of the project was to divert the river channel away from the work area to construct a haulage cycle area. This was followed by building up a diversion bund to cut off existing channel in the work area. Importantly a culvert system and raised gravel crossing were constructed to ensure that heavy vehicles were at no stage working within any residual flows that might permeate through the diversion bund. The 45T Excavator removed some excess vegetation which was carted away to appropriate fill site. The Engineer undertook a site inspection of the proposed stopbank foundation setout as a hold point in construction. A Plateau Density Test (PDT) was carried out on the first layer which determined a reference Maximum Dry Density for the remaining stopbank construction with additional NDM testing as per specified frequency.