Defect Level Condition Modelling of Sewer Pipes

Z. Tizmaghz, J. E. van Zyl, T. F. P. Henning (University of Auckland)

N. Donald (Watercare Services)

P. Pancholy (University of Canterbury)

Sewer pipes are affected by various internal and external factors and therefore need to be maintained and monitored to keep their performance at a desirable level. CCTV plays an essential role in monitoring, assessing, and condition scoring sewers. A condition score is assigned to each sewer pipe based on the type, quantity, and extent of defects observed through CCTV inspections. While the impact of different factors on the condition score has been considered in several studies, the impact of these factors on the underlying defects has not been investigated in detail. The aim of this study was to investigate the effect of various factors, including age, diameter, and slope on the prevenance of eight defect categories in the transmission sewer network of Auckland, New Zealand. A cleaned dataset with the defects identified through recent CCTV inspections of 2817sewers was gathered and linked to a range of physical and environmental factors. Defects were grouped into the following eight categories: gas attack, material damage, infiltration, roots, debris, total joint, structural, and dipped pipe. Results identified statistically significant relationships between defect categories and factors that provide new insights into the drivers of deterioration processes in sewer pipes.