KiwiRail engaged PDP to provide culvert design and consenting services for ten culverts along the main North Island railway lines identified as high priority due to capacity issues, collapse or blockage, fish passage barriers, and maintenance issues.
Between late 2022 and mid 2023, PDP conducted condition assessments for each culvert, hydrological modelling of the catchments, evaluation of the hydraulic capacities, and provided replacement/remediation recommendations. These recommendations were also informed by ecological and wetland assessments, planning assessments, and geotechnical investigations and slope stability analysis.
PDP and KiwiRail determined that seven culverts required replacement and further detailed design, which PDP completed. Two complex culverts were identified, including one with a high embankment depth/slope instability. Three culverts required consent due to coastal environments, presence of wetlands, or significant ecological areas (SEA).
A key project challenge arose for upgrading one culvert located on a very steep and unstable site with a natural wetland directly downstream. PDP value engineering and client workshop discussions resulted in design amendments including a 9m inlet shaft, micro-tunnelling through largely competent material, ground anchoring and Council accepting offset planting for the outlet structure area which encroached into the natural wetland.
Key Contacts
Luke Matheson
