This paper presents a methodology for the digital reconstruction and management of underground utility networks in urban environments through Building Information Modeling (BIM) integrated with UAV photogrammetry, laser scanning, and Ground Penetrating Radar (GPR). The novelty of this study lies in the structured workflow that combines international standards (ASCE/UESI/CI 38-22, PAS 128:2022) with cloud-based platforms to ensure interoperability, information quality, and traceability across the entire infrastructure lifecycle. Compared to previous studies, this work explicitly addresses uncertainty in data acquisition and demonstrates the integration of heterogeneous survey techniques within a federated BIM model. The case study at the University of Palermo validates the approach, showing improvements in accuracy, data governance, and collaborative decision-making. The contribution of this work is the establishment of a reproducible framework for Digital Twins in Smart Cities, enhancing urban planning, risk management, and sustainable infrastructure maintenance.