WCC Central City Stormwater Upgrade

Spencer Holmes Limited were the site surveyors for Harker Underground Construction Ltd who were engaged by the Wellington City Council to lay a new stormwater drain along Wellington’s busy central city streets.

The project involved the construction of a new stormwater drain using pipe jacking technology. The main drain is a 1500mm ID reinforced concrete pipe laid at depths of up to 13 metres below sea level. It starts at the harbours edge by the entrance to the lagoon and heads inland towards Willis Street.

Due to the proliferation of underground services within our city streets it was a major undertaking for the contractors to relocate only those services that conflicted with the pit locations.
The cost of clearing a route for open trenching would have been prohibitive. Furthermore, open trenching would have caused much greater disruption to traffic.

The overall level of accuracy required at breakthrough was not unduly high - within 50 millimetres was considered acceptable.

"As near as I could determine, it was dead on for line and about 20mm out for height" said Hudson.

"The sight of seeing that tunnelling machine break out into the receiving pit at the right spot makes it all worthwhile and leaves me with a feeling of great satisfaction".
Hudson Moody led the Spencer Holmes Limited surveyors to:
  • Establish a horizontal and vertical control network along the route of the drains.
  • Complete a topographical survey to fix all existing services, kerbs and street furniture in the vicinity of each pit to facilitate the design and relaying of affected services.
  • Set out the pit positions and established a height datum for each.
  • Undertake level and alignment checks during the course of each drive.
  • Establish levelling pins along the road surface to monitor for subsidence. Prepared as built plans.
  • Set out the design alignments on the surface and transferred into the pits to allow the beds to be positioned.