Comprehensive Sewer Condition Assessment Using CCTV and Electro Scan: International Cases

On February 22, 2011, Christchurch, New Zealand experienced a magnitude 6.4 earthquake, killing 185 people in one of the country's deadliest peacetime disasters. The total cost to insurers has been estimated between $15-20 billion, making it New Zealand's costliest natural disaster and the third-costliest earthquake, worldwide. The earthquake caused widespread damage, especially in the central city and eastern suburbs, with buildings and infrastructure already weakened by a previous earthquake occurring September 4, 2010. The February 22nd earthquake caused significant liquefaction affecting the eastern suburbs and producing 400,000 tons of silt. While a conglomerate of diverse partners formed the Stronger Christchurch Infrastructure Rebuild Team (SCIRT) to assess the damage and undertake emergency repairs of public infrastructure and right of way, little focus has been dedicated to the condition assessment of underground infrastructure of property homeowners and educational institutions. While smaller diameter pipes were oftentimes inspected using high resolution push cameras, the inability of visual inspection techniques to adequately identify and quantify cracks and defects led consultants for the Ministry of Education to utilize a new technology, known as "electro scanning", to reassess previously televised drains. This paper describes the limitations of using closed-circuit television (CCTV) camera equipment and compares side-by-side results from electro scanning. By measuring the variation in electric current flowing through defects in non-conductive pipe walls, this paper explores the type of data, field set-up requirements, and diagnostic information resulting from both legacy CCTV and new electro scan technologies.