Steep private properties, un-engineered fill and an inaccessible stormwater outlet ruled out conventional construction methods in this stormwater upgrade.
Kerry Drainage & Civil developed a trenchless solution using its Pit Drill, navigated unexpected underground obstructions and installed New Zealand’s first DN375 PVC Restrain pipe.
Kerry Drainage & Civil was engaged by Healthy Waters as the main contractor for the Teal Crescent Stormwater Upgrade. KDCivil was also involved during the design phase, providing investigation and methodology advice to help develop a practical solution for the challenging site.
Two sections of the existing public stormwater network had partially or completely failed, with the affected pipelines running across multiple private properties on steep terrain. The project involved installing three new stormwater pipelines, alongside additional street drainage, replacement of a gravity retaining wall, a new stormwater outlet and slope stabilisation works.
The location and ground conditions made conventional open-cut construction particularly challenging. Much of the work was on steep private property with areas of un-engineered fill, while the depth to invert and site constraints meant that conventional directional drilling was not viable.
KD Civil instead developed a solution using its Pit Drill, allowing the new pipelines to be installed trenchlessly while working within the tight site constraints.
The downstream section presented particularly difficult drilling conditions. The drill alignment encountered numerous unexpected obstructions, including timber piles and car parts buried within the ground. These were carefully cleared using a combination of hand excavation and hydro-excavation before the new 450mm OD HDPE pipe was pulled into position.
Ground conditions were more favourable on the upstream section, but the new pipeline still had to navigate around an existing timber pole retaining wall. To suit the constraints of the installation, Kerry Drainage & Civil selected DN375 PVC Restrain pipe for this section. The project marked the first installation of DN375 PVC Restrain pipe in New Zealand.
The stormwater outlet created another significant access challenge. Located at the base of a steep slope with no suitable excavator access, the outlet had to be constructed largely by hand. Materials were lowered to the work area using an excavator and winch, allowing the team to safely construct the outlet despite the difficult terrain.
By combining specialist trenchless equipment, careful investigation and practical problem-solving, Kerry Drainage & Civil was able to deliver the new stormwater infrastructure while working across steep private properties and around challenging existing structures and ground conditions.
