Replacing critical stormwater infrastructure beneath a residential neighbourhood
Following the significant flooding experienced across Auckland in February 2023, damage was identified to a 900mm stormwater pipeline beneath Castleton Street in Birkdale.
The pipeline formed part of an important overland flow path through a residential subdivision, and its failure had the potential to increase flood risk for surrounding properties.
The challenge was significant. The existing pipeline sat approximately 6.5–7m below ground, beneath a residential street and private properties, with limited working space and existing services adding further complexity. The site was also close to a local primary school, making safe access and minimising disruption to residents and pedestrians an important consideration throughout the works.
Changing the methodology when the conditions demanded it
The initial proposal was to replace the damaged pipeline using pipe bursting, which would have reduced the amount of excavation required.
Kerry Drainage & Civil worked through the options with the project team and changed the construction methodology to an open-trench replacement.
However, as the works progressed, investigations revealed approximately 500mm of concrete bedding surrounding the existing pipe. This would have created significant resistance to the pipe-bursting operation and potentially caused the new pipe to deviate from its intended alignment.
At depths of up to 7m, this required careful planning of the excavation, temporary works and plant positioning. An engineered shoring system was developed to safely accommodate the depth of the excavation and the surrounding services.
An existing Auckland Council watermain presented another significant constraint. Rather than excavating directly beneath it, Kerry Drainage & Civil adopted a tunnelling approach supported by a temporary bridging platform, allowing the stormwater works to continue while protecting the existing watermain.
The project also included the construction of a new 1.8m diameter, 6.7m deep stormwater manhole and approximately 60m of CIPP lining to the existing downstream pipeline.
Restoring the network and reducing future flood risk
The completed works replaced the damaged 900mm stormwater pipeline, added a new 1.8m diameter manhole and rehabilitated the downstream network with CIPP lining.
Together, these works restored the integrity and capacity of the stormwater network and reduced the risk of future pipeline failure and flooding within the surrounding residential area.
The project demonstrated the importance of adapting construction methodology to the conditions found underground — combining detailed investigation, engineered temporary works and practical construction experience to find a safe and workable solution in a highly constrained environment.
