Advanced post-earthquake damage assessment for non-pressurised pipes. Learning from the Canterbury (NZ) earthquake sequence 2010-2011

Non-pressurised pipes, commonly used within gravity driven storm water and wastewater networks, are very vulnerable to earthquakes. The consequences potentially caused by the earthquake-induced damage to both pipes storm water and waste water networks could be highly impacting in the short and long term, including health issues to the impacted population and increased flooding vulnerability in the impacted area. Therefore a reliable preevent seismic vulnerability assessment and a precise, though rapid, post-earthquake damage assessment for non-pressurised pipes is critical. Empirical fragility relations have been commonly used for predicting expected damage for buried pipes for both pre-disaster vulnerability assessment purpose and for informing post-disaster impact assessment and therefore repair/reconstruction decision making. However different shortcomings still affect fragility relationships and their use for the aforementioned purposes. The availability of advanced survey techniques and data management software is opening new opportunities towards a precise damage and impact assessment for buried pipes post-earthquake and therefore towards an optimal repair/reconstruction decision-making process, as demonstrated after the Canterbury Earthquake Sequence (CES) 2010-2011 in New Zealand. However, such a detailed level of damage and impact assessment might be very time-consuming and expensive and therefore unaffordable at large scale. This paper, after providing a nonexhaustive, but effective, overview on both fragility relations and advanced survey techniques, compare the outcomes from both the approaches and discuss their weaknesses and potentialities in relation to a case study, identifying with a selected portion of Christchurch, New Zealand, storm water system. The projecting of the outcomes from damage assessment with advanced survey techniques, conducted in confined selected areas, using empirical models is envisaged to become an optimal compromise towards accurate although time and cost-effective post-earthquake damage and impact assessment