Digital twins for urban underground space

Digital twins (DTs) offer promising benefits to address several inherent problems in underground construction, yet confusion surrounds the concept due to its context-specific nature which hinders more widespread adoption. This paper seeks to clarify DT-related terminologies from a built environment perspective and define the features and maturity levels of DTs for underground spaces, considering their unique challenges. A layered architecture for constructing DTs is proposed, offering various options based on functionality, technological advancement, and expected value. Additionally, a comprehensive literature review of technologies enabling the development of digital twins for underground spaces is presented, including data-driven ground modelling, site investigation and design process integration with BIM, computational BIM, and advanced sensing and instrumentation. The paper identifies synergies between DTs and the observational method in geotechnical engineering, highlights research gaps, and proposes a transition to a prescriptive, knowledge-based DT. Furthermore, exemplar use cases of underground DTs throughout their lifecycle are explored, demonstrating their potential value.