In subsurface planning of urban areas, the use, management, and exchange of urban and geological data serve as a fundamental basis for collaboration among various specialist in the fields of urban and geological 3D modeling. Therefore, the development of a data model schema tailored to urban and geological subsurface models is an important foundation for data management. However, various information’s about buildings, infrastructures, and geological structures, that cannot be integrated in common data model structures requires an expansion and combination of the existing data model structures for geological and urban 3D models. The existing data model schemas can already manage various types of subsurface data. Building on this, this paper aims to advance the development of a data model by combining existing schemas to meet the requirements for data management in 3D voxel modeling of the subsurface. The conception of such a data model is implemented for a case study in the City of Stuttgart, based on the GML application schemas Geoscience Markup Language (GeoSciML) and City Geography Markup Language (CityGML). Our data model is applied using urban and geological model elements for the Stuttgart case study. In this context, the construction and integration of the model elements within a framework that comprises modeling, data management, and visualization tools were examined.