The central requirement of project safety, stability, and resilience of complex underground systems leads to demands for more efficient computational modelling tools to assist design and decision-making during the project life cycle. The concept of Digital Twins (DTs) provides a robust solution to monitor a construction project during its life cycle, predict its behaviour based on integrated holistic computational models, and protect it from hazards by virtually controlling the physical processes with its digital counterpart. Leveraging the power of a computational framework based on CutFEM combined with a BIM platform incorporating CAD-based data, the TwinSSI project will develop a comprehensive DT for underground design and construction. To validate the computational framework, real-scale experiments of tunnel-soil-structure interaction will be performed at the National Buried Infrastructure Facility (NBIF) at UoB. Moreover, the developed DTs will be applied to real case studies co-created with the industrial partners Network Rail and Maidl Tunnel consultants. The TwinSSI project will thus, for the first time, create and validate detailed DTs in the domain of soil-structure interaction modelling. The project outcomes will lead to a new paradigm for project planning and monitoring by geotechnical engineers.