Christchurch City Wastewater Infrastructure - Response Assessments and Repair Techniques

This paper looks at the assessment processes and repair techniques utilised to stabilise the wastewater network and maintain service to the residents of Christchurch. At May 2013 Council had spent a total of $155 million on earthquake wastewater repairs and maintenance. $65 million has been utilised solely on repairs and stabilisation of the wastewater network.

The majority of damaged infrastructure occurred in recent marine sediment deposition areas. Earthquake induced liquefaction resulted in higher than “business as usual” operational costs and increased risk of wastewater overflows to waterways. Once the network was sufficiently cleared of debris, pipe assessments were undertaken covering immediate and longer term requirements.

The assessment processes utilised included pole camera, CCTV and the sewer leak technology of electro scanning. Repair techniques utilised include traditional dig and lay, pipe lining and patching, pipe bursting and pipe insertion, and the injection of compound resins around the pipe exteriors. The compound injection technique was utilised in areas of high ground water infiltration where dig and lay would have required considerable dewatering, resulting in significant costs and longer term disruption. A subset of each repair treatment system was assessed against ground and local environmental conditions, particularly depth to pipe, liquefaction index, pipe material and disruption to communities.