Journal of Safety and Environment

To address the insufficient characterization of cross-layer risk transmission and differential facility exposure in urban underground spaces， this study proposes a three-layer coupled network consisting of risk factors， disaster events， and facility types. The network structure is established by representing the relationships among different risk elements and describing the cascading transmission pathway from initial risk factors to disaster consequences and facility impacts. A cascading failure model is developed to simulate the dynamic propagation process among interconnected nodes. Specifically， risk propagation pressure is introduced to quantify the transmission intensity between nodes， while node tolerance thresholds are defined to represent the resistance capacity of individual nodes against cascading failures. Based on the proposed mechanism， a method for identifying key cascading risk sources is developed， and a facility exposure assessment index is constructed to quantify the heterogeneous exposure characteristics of different underground facility categories. The proposed method is validated using 200 representative accident cases collected in China from 2010 to 2025. The identified key cascading risk sources are compared with frequently reported accident causes， and the calculated facility exposure index is further compared with actual damage frequency. The results show that lax safety management， operational errors， and equipment aging or corrosion play important triggering roles in risk propagation. Among different facility categories， underground pipelines exhibit the highest exposure level， whereas underground passageways show the lowest exposure level. The consistency rate between the identified key cascading risk sources and frequently reported accident causes reaches 66.7%， and the facility exposure index demonstrates a significant correlation with actual damage frequency， with a Pearson correlation coefficient of 0.706. Furthermore， the comparison between cascading influence and topological centrality indicates that structural importance does not necessarily correspond to cascading propagation capability. The proposed method provides an effective approach for disaster chain interruption， critical facility monitoring， and hierarchical risk management in urban underground spaces.