Work undertaken included:
- Construction of a large precast stormwater outfall through the seawall at St Heliers beach.
- Installation of precast box culverts.
- Installation of a two-metre diameter stormwater pipeline along The Parade and across Tamaki Drive.
Working between high tides, we used a crane to place the 12-tonne outlet units on a pre-constructed concrete bed. A feature of our innovative approach to this job was the concrete cut-off wall we constructed behind the sea wall to limit tidal ingress to the worksite. This enabled work to continue independent of tides, and thus be completed quicker and with less disruption to the public.
To minimise disruption to traffic and residents, we used a 70-tonne hydraulic excavator (rather than a crane) to install 10-tonne culverts into the trench. The sides of the excavation were supported using a purpose-built steel trench shield that protected the immediate work face – and our personnel – in a restricted space. We overcame several challenging features of this project. We worked safely and cost-effectively on site with a combination of:
- Poor ground conditions (sand, tidal inundation, high water table, an old stream bed littered with debris such as logs and mud).
- A sensitive marine environment that is also a high-profile and popular recreation beach close to a residential area.
- An arterial road (Tamaki Drive) linking Auckland’s eastern suburbs with the city.
- Handling of contaminated material.