On New Zealand's largest wastewater project, a liner delivery delay threatened a 76-metre deep shaft. Blick designed a fluid system that kept it stable for 91 days beyond design specifications.
The Challenge
New Zealand's largest bored wastewater tunnel — the $1.2 billion Central Interceptor, 14.7km and 4.5m diameter running 15–110m deep — required large-diameter shaft support at Keith Hay Park. When the shaft liner's delivery was delayed, CLL's 76-metre deep shaft needed to stay open for 62 days beyond its 90-day design specification. Collapse was not an option on a project of this scale.
The Approach
Blick designed a unique bentonite-based shaft support fluid system using Wyo-Ben MAX GEL and M-I SWACO UNITROL filtration control polymer. The system created a thin, stable filter cake that prevented fluid infiltration while providing full hydrostatic support. Critically, viscosity had to stay below 38 seconds Marsh to allow SHAPE sonar equipment to accurately assess excavation dimensions — a constraint that required careful reformulation.
The Outcome
The shaft held for 152 days total — 90 days design life plus 62 days beyond specification — with no deterioration. The thin filter cake prevented fluid migration throughout. 'Thanks to Blick and the excellent support of their technical support team, we had a successful outcome from start to end of the shaft drilling at Keith Hay Park.' — Sivam Thivaharan, Site Engineer, CLL Service and Solutions.