The existing Mairangi Bay pump station could no longer cater for the new development in the area and was overflowing onto nearby beaches.

Pipeline & Civil engaged us post award to optimise the geotechnical design. An opportunity was quickly identified to delete all of the tensioned ground anchors included in the tender design by optimising the base slab of the tank. This was achieved by allowing transfer of the uplift loads, associated with long-term hydrostatic forces on the underside of the tank in the permanent design case, into the surrounding ground retention piles.

Our team used state-of-the-art 3D finite element modelling to demonstrate that this transfer would further allow for a reduction in the reinforcement requirements of the base slab. It also demonstrated that the internal partitional walls would essentially prop the base slab prior to groundwater equalising to its long-term steady state conditions. In addition, our analysis optimised all reinforcement requirements

of the other structural components. That analysis identified for the structural engineers all unfactored shear force, bending moment and axial forces in all of the structural members.