A network-of-networks percolation analysis of cascading failures in spatially co-located road-sewer infrastructure networks

This paper presents a network-of-networks analysis framework of interdependent critical infrastructure systems, with a focus on the co-located road-sewer network. The constructed interdependency considers two types of node dynamics: co-located and multiple-to-one dependency, with different robustness metrics based on their function logic. The objectives of this paper are twofold: (1) to characterize the impact of the interdependency on networks’ robustness performance, and (2) to unveil the critical percolation transition threshold of the interdependent road-sewer network. The results show that (1) road and sewer networks are mutually interdependent and are vulnerable to the cascading failures initiated by sewer system disruption; (2) the network robustness decreases as the number of initial failure sources increases in the localized failure scenarios, but the rate declines as the number of failures increase; and (3) the sewer network contains two types of links: zero exposure and severe exposure to liquefaction, and therefore, it leads to a two-phase percolation transition subject to the probabilistic liquefaction-induced failures. This indicates that tiered vulnerability of the liquefaction-prone links will result in multiple percolation transitions. The proposed framework provides a holistic approach to analyze the network robustness under different failure scenarios and can be extended to a larger interdependent system.