Liquefaction fragility of sewer pipes derived from the case study of Urayasu (Japan)

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.

Probabilistic seismic damage and loss assessment methodology for wastewater network incorporating modeling uncertainty and damage correlations

“…More recently, fragility functions have been developed in terms of damage ratios per unit length, such as the number of faults per km, to account for materials unique to wastewater systems (e.g. for Hume, VU, VP, PVC, and tile pipes (Shoji et al, 2011) and AC, CI, CONC, EW, RCRR, PVC, and PE pipes (Liu et al, 2015;Nagata et al, 2011)), functional disruption length per km (Shoji et al, 2011), and repair rate, defined as the number of repairs per km, with respect to peak ground velocity (PGV) or liquefaction potential index (LPI) (Baris et al, 2021). Furthermore, although ALA (2001) fragility functions, which are considered the industry standard for assessing the seismic vulnerability of pipelines, provide variability of pipe fragility in terms of lognormal standard deviations, fragility functions based on median repair rates are widely used for the seismic assessment of pipelines in practice, by industry and research communities alike (Makhoul et al, 2020;Sigfu´sdo´ttir, 2020).…”

“…Compared to the large body of literature related to the seismic assessment of other lifeline network systems, only a few of studies have assessed the seismic performance of wastewater systems; e.g., in contrast to potable water distribution systems (Cimellaro et al, 2016; Farahmandfar et al, 2017; Farahmandfar and Piratla, 2018; Fragiadakis and Christodoulou, 2014; Mazumder et al, 2020). Generally, existing studies on wastewater systems can be classified as: (1) reconnaissance studies reporting damage sustained to wastewater systems and the associated factors contributing to the vulnerability of the pipelines (Eidinger and Schiff, 1998; Eidinger and Tang, 2011; Giovinazzi et al, 2015; Scawthorn et al, 2006; Sherson et al, 2015; Zare et al, 2011), (2) empirical studies developing fragility functions for wastewater pipes based on reconnaissance observations (Baris et al, 2021; Liu et al, 2015; Nagata et al, 2011; Shoji et al, 2011), and (3) analytical studies evaluating the seismic performance of wastewater systems (Makhoul et al, 2020; Sigfúsdóttir, 2020; Sousa et al, 2012). Findings have included: (1) the predominant mode of failure is floatation of the pipes or manholes, due to differential settlements caused by liquefaction, (2) pipe failure decreases with increasing diameter and burial depth, and (3) some pipe materials, such as asbestos cement (AC), unreinforced concrete (CONC), cast iron (CI), earthenware (EW), and reinforced concrete with rubber rings (RCRRs), are inherently more vulnerable than other pipe materials, such as polyethylene (PE), polyvinylchloride (PVC), or high-density polyethylene (HDPE) (Giovinazzi et al, 2015).…”

“…Despite the damage observed after past earthquakes, little effort has been made to collect the data necessary to develop empirical-based fragility models for wastewater pipelines (e.g. Baris et al, 2021; Liu et al, 2015; Nagata et al, 2011; Shoji et al, 2011). Moreover, little to no effort has been made to collect data to inform pipe damage correlation models for wastewater pipes (e.g.…”

“…More recently, fragility functions have been developed in terms of damage ratios per unit length, such as the number of faults per km, to account for materials unique to wastewater systems (e.g. for Hume, VU, VP, PVC, and tile pipes (Shoji et al, 2011) and AC, CI, CONC, EW, RCRR, PVC, and PE pipes (Liu et al, 2015; Nagata et al, 2011)), functional disruption length per km (Shoji et al, 2011), and repair rate, defined as the number of repairs per km, with respect to peak ground velocity (PGV) or liquefaction potential index (LPI) (Baris et al, 2021).…”

Settlements and angular distortions of shallow foundations on liquefiable soil

“…Seismic liquefaction continuously stimulates the interest of the geotechnical community in promoting experimental, theoretical studies and eld observations that clarify the factors ruling susceptibility of soil, triggering (e.g., Ishihara, 1996 Baris et al, 2021) or at conceiving mitigative solutions (Flora et al, 2021;Salvatore et al, 2020), motivated by the concern of stakeholders for the huge economic and social impact of liquefaction recorded in past seismic events. An overall estimate is provided by Daniell et al (2012) who disaggregated primary (shaking) and secondary causes (tsunami, re, landslides, liquefaction, fault rupture, and other type losses) over a global record of nearly seven thousand earthquakes from 1900 to 2012.…”