United Tunneling was engaged to deliver a trenchless installation beneath the North Island Main Trunk (NIMT) twin rail line at Ngaruawahia. The works required a controlled crossing beneath an active rail corridor, where maintaining rail operations and ensuring ground stability were critical.
The project involved 40 metres of 1000mm steel pipe installed using auger boring at 2.5 metres depth, with an 800mm SDR21 PE pipe installed inside the steel casing. Sheet piling was used to form and support the excavation areas, providing a stable working platform for the bore entry and exit pits.
Working beneath live rail infrastructure required careful planning, strict safety controls, and precise execution to ensure the installation was completed without disruption to rail services above.
This type of work reflects the value of trenchless methods in critical infrastructure environments — delivering essential underground services while keeping transport networks running above ground.
Project highlights
Project: Ngaruawahia rail crossing
Location: NIMT Twin Rail Line
Method: Auger Boring
Support Works: Sheet Piling
Length: 40m
Pipe Size: 1000mm steel casing with 800mm SDR21 PE pipe
Depth: 2.5m
Launch Box: 12m L x 5m W x 4m D
Environment: Live rail corridor
Need a trenchless solution under rail or critical infrastructure?
Talk to the United Tunneling team about the right approach for your next project.
