Energy geostructures integrate the primary ground heat exchangers of ground-source heat pump (GSHP) systems within foundation or support elements, as well as tunnel linings. We present a digital twin framework for the smart operation of a 3 km cut-and-cover thermoactive urban tunnel currently under construction in Madrid. The tunnel's diaphragm walls will not only serve as structural support but will also function as a large modular closed-loop ground heat exchanger. Several GSHPs will be installed to provide heating and cooling to adjacent buildings. By hybridizing GSHPs with conventional HVAC systems, multiple power-sharing options will be made possible. The digital twin offers a solution for managing the dynamic availability of geothermal resources, influenced by prior exploitation, operational thresholds, weather conditions, and varying energy demands. It encompasses the tunnel (including the diaphragm wall and surrounding ground as the physical component), temperature, deformation, and pipe circuit sensors (for data collection), pipe circuit operators (for automation), a numerical model (as the virtual component), data transfer protocols and devices, and the service: The real-time decision-making to optimize energy management. In this presentation, we focus on the service enabled by the digital twin and the opportunities that it presents for smart operation. The digital twin allows for continuous calibration and accurate prediction, overcoming challenges posed by simplified ground models due to uncertainties and variability in soil properties and the differing boundary conditions found along the 3 km tunnel.