DG43B – A Pain in the Asset

A partnership between the Christchurch and Government agencies was established in 2011 with the intention of repairing earthquake damaged horizontal infrastructure. The earthquakes weakened 1600km of brittle pipes, ~65% of the total wastewater infrastructure, but left them in a “just operational” level of service. Under the Design Guide (43b) the basic principle was, if a pipe could last more than five years it was left to the Asset Owner to manage, which has resulted in inconsistencies to repairs in parts of the network. With wastewater overflows to waterways being unacceptable and a programme of maintenance required, a multi-pronged team approach including regular detailed monitoring of 20 targeted wastewater pipe reference sites was employed. This was overlaid against the wastewater network with approximately two thirds having CCTV at 95% or greater accuracy against the NZPIM.

Findings include conclusive evidence of pipe decay rates, on the edge of performance failure but still operating acceptably. Assets that show large signs of earthquake damage but would have otherwise remained in good condition for the majority of the service life are in critical but stable condition. Whereas assets with a combination of earthquake and significant service damage (high level roads, liquefiable areas, higher number of connections) have evidence of linear or non-linear increases to deterioration rates.

With this data, the Asset Owner can improve its maintenance scheduling efficiency, decisions on renewals and minimise assumptions of remaining asset life with confidence. In particular the Asset Owner is able to target its maintenance spend and sweat the asset. The valuable evidence obtained allows accurate profiling of decay, directly informing operations and multi-million dollar renewals profiles for these pipes. The Asset Owner can then refine its funding profiles and target its limited funding to areas where dry weather wastewater overflows have affected aquatic systems and water users.

There are nationally significant outcomes, including adoption of the assessment model and methodology for networks with little asset information. With five years of data for selected wastewater reference sites, strong correlations can be made between the ratio of earthquake to normal service damage and the remaining life of the asset. The results of this have large implications on priorities for operation teams and criticality for asset management services.