Identifying implementation-oriented models of urban underground space development in China based on fuzzy-set qualitative comparative analysis (fsQCA)

The rapid expansion of urban underground space (UUS) has become increasingly popular in densely populated urban areas worldwide. Although data-driven technology has facilitated the planning process successfully, the implementation mechanism of UUS planning remains obscure, potentially undermining the spatial performance. To address this gap, this study employs fuzzy-set qualitative comparative analysis (fsQCA) to analyze the causality of UUS development. Three primary models of UUS development-separate, interconnected, and integrated models-are categorized. Causal conditions and outcomes along with their quantitative metrics are proposed. Subsequently, 30 Chinese cases are analyzed using fsQCA to assess the necessity and sufficiency of UUS development. Three distinct causal paths are identified, namely strong economic strength, robust policy support, and advanced construction technology, which play critical roles in integrated development, while weak economic strength and inadequate policy support lead to separate development. The study underscores the importance of implementing UUS development models and provides valuable insights for UUS planning management.