The purpose of the project was to address flooding problems by installing two stormwater pipelines under the North Island Main Trunk Line at Pukekohe.
This involved trenchless installation of a 1050mm concrete pipe under the live rail corridor and installation of another 660mm GRP pipe under the same line to a depth of 5m over a distance of approximately 95m.
Another 250m of open cut pipe, varying in diameter from 600-1350mm was also installed next to the railway lines.
This project presented several challenges as all of the trenchless works had to be done during live rail operations and with minimal disruption to the travelling public. This involved liaison with numerous stakeholders, notably KiwiRail, Council’s stormwater team, Auckland Transport, Transdev and Housing New Zealand.
The geotechnical conditions presented a challenge for the deep excavation works, as the ground had a high water table with associated risk of water drawdown, excavation collapse, and flooding.
Potential ground settlement due to vibration from the works, which could lead to movement of the railway tracks and major disruption to the line, was also identified as a critical risk.
The need to minimise vibration and ground settlement was a major constraint. Surveys were undertaken every two hours to identify any ground movement. Our careful planning and risk management prevented this from escalating into an issue that would disrupt live rail operations.