Hutt Valley outfall pipe repair

A key feature of the Hutt Valley wastewater system is an 18.3 kilometre land based outfall pipeline. A pump control malfunction in March 2009 resulted in five joint failures and the start of a major repair and investigation lasting four months. The traditional response involved open excavation and casting reinforced concrete blocks around the leaking joints.

Difficult access to some of the sites led to a proprietary internal joint sealing system from Germany being used. The internal seal technique has significantly improved the speed and reduced the disruption to public compared to the previous repair approach. In addition this provides a cheaper repair and a better technical solution that maintains flexibility of the joint.

During the repair works, condition inspections were undertaken of the pipes and joints, and an innovative system was developed to pressure test the existing rubber ring pipeline joints. Following the initial recommissioning, a second major failure was discovered caused by tree roots that had affected some pipes. That failure required a structural slip lining repair to be made.

This paper describes the investigations undertaken during that period, the challenges of planning and completing a repair and the innovative repair methods that were developed.