Liquefaction fragility of sewer pipes derived from the case study of Urayasu (Japan)
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Liquefaction fragility of sewer pipes derived from the case study of Urayasu (Japan) Anna Baris1 · Rose Line Spacagna1 · Luca Paolella1 · Junichi Koseki2 · Giuseppe Modoni1 Received: 19 March 2020 / Accepted: 8 September 2020 © Springer Nature B.V. 2020
Abstract The damage on supply and drainage water networks is a serious cause of economic disruption for urban systems affected by earthquakes. Among various concerns, the ruptures of sewer pipes and manholes generated by liquefaction determine a particularly severe sanitary hazard and require extensive, costly and time-consuming repairs. Quantitative risk assessment carried out with the characterisation and geographical mapping of seismic hazard, subsoil susceptibility, physical and functional vulnerability of the exposed elements, enables to estimate losses, identify weaknesses, inspire strategies to mitigate the impact of earthquakes and improve resilience. The present study deals with the physical vulnerability of sewer pipelines. Empirical fragility functions are derived from the evidences of liquefaction induced in Urayasu (Japan) by the 2011 Tohoku-Oki earthquake (Mw9.0). The spatial distribution of seismic signals, subsoil characteristics, pipes and surveyed damages are reconstructed in a GIS platform. An articulated methodology is developed to correlate variables and compensate their limited spatial correspondence, exploiting the complete coverage of the area with terrestrial settlements measured by LiDAR and their strong correlation with damage. Finally, ruptures of pipes are probabilistically quantified adopting a common liquefaction severity indicator as engineering demand parameter and measuring the efficiency of relations with statistical tests. Keywords Liquefaction · Sewerage · Subsidence · Vulnerability · Validation
1 Introduction The ruptures on water delivery or draining systems determine a particularly severe economic impact on the communities affected by earthquakes, as long time and huge expenses are required to rehabilitate networks spread over wide geographical areas (Jones et al. 2008). Risk is noticeably higher in zones prone to liquefaction, because buried elements (pipes, manholes, pumping and regulation plants) undergo additional horizontal * Anna Baris [email protected] 1
University of Cassino and Southern Lazio, Cassino, Italy
2
University of Tokyo, Tokyo, Japan
13
Vol.:(0123456789)
Bulletin of Earthquake Engineering
displacements due to the degraded stiffness of the cyclically loaded granular soil (e.g. Salvatore et al. 2016, 2018) and vertical movements due to sinking or buoyancy (e.g. Castiglia et al. 2020). For the city of Christchurch (New Zealand) struck by the Mw6.2 earthquake in February 2012, O’Rourke et al. (2014) report repair rates of freshwater pipelines equal to 1.68 cases per kilometre (n/km) in the liquefied zones, 0.27 n/km in the non-liquefied zones. For wastewater conduits, the repair rate was 1.06 n/km for the liquefied zone versus 0.12 n/km for the non-liquefied zones. These data represent only gl
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