Mairangi Bay Pump Station

Description

The existing Mairangi Bay pump station can no longer cater for the new development in the area and was overflowing onto nearby beaches. Pipeline & Civil were engaged to construct a new pump station, installing larger pumps and additional underground storage that could hold wet weather flow, until they can be pumped into the network.

Work commenced onsite in May 2021, with the team completing the service diversions to allow space to be cleared for the new underground shaft of the pumpstation, this was completed in December 2021 with wastewater, water and power services being relocated.

In 2022 concrete secant piling (completed by CLL) to form the permanent underground structure, was completed. As too was the excavation of the 12m deep shaft and construction of the floor, which is 1.6m thick in places. The team then moved on to the outer skin wall. Being circular in shape and being cast directly against concrete piles, single sided jump formwork had to be used which was a particularly complicated feat of engineering to assemble and place.

On completion of the outer skin, steel work for the dividing walls began as well as preparing the new formwork for these dividing walls. The major central dividing wall which separates the dry well and wet well was poured using double-sided formwork, which progressed the project significantly.

Eight concrete plinths that were poured in conjunction with the middle wall. These plinths are where the four new wastewater pumps will rest, taking the wastewater from the wet well, and pumping it to Watercare’s wastewater treatment plant in Rosedale.

At the end of February 2023, the Mairangi Bay pumpstation project had progressed well and reached some key milestones. The underground shaft which contains the drywell and wet well is structurally complete, with only the roof to be finished. The internal walls are finished and all pipe penetrations through the piles to the outside are complete, including the inlet gravity sewer pipe, the rising main and the odour ventilation duct.

The main structural hollowcore beams were installed onto the roof of the wetwell and dry well, these will later be joined by unispan slabs. After the unispan slabs are installed, it will mean that the underground shaft is completely covered over, at which point a concrete pour to completely encapsulate the roof will take place.

The next step is the mechanical fit out of the dry well. Pipe support, pipework, pumps, and valves are all installed. Steel beams for the gantry cranes and the platform installation will then take place. Following the installation of everything underground, the roof will be placed on the top and then the construction of the pumpstation building will commence, which has been architecturally designed to improve the visual appearance of the area.

Manhole 5 excavation will also be completed in 2023. This manhole will sit outside the pumpstation and will be the link point between the upstream gravity sewer and the pumpstation. The manhole and the link between to MH3 will complete the gravity sewer portion of works.

Works will also commence on the new wastewater pipeline on Montrose Terrace that will help improve the flow of wastewater from the area into the new pumpstation.

Senior Project Engineer –  Daniel Matthews

Project Engineers – Gonzalo Aparicio and Aliasger Zamani

Site Engineer – Abhinav Tomar

Engineering Intern – Liam Thornton