Over the years, in order to meet the many and growing needs of urban development, a lot of underground spaces have been used for the public infrastructures, such as utility lines, rail lines and roads. Complex underground infrastructure and inaccurate underground information complicate the development of underground space, the ownership of underground objects is not clear for example; the interdependency of above ground and underground has not presented directly, another example. Having said that, some countries and institutions have implemented or at least conceptualized the 3D mapping of underground utility network and their management in relation to the cadastral system. The City of Zurich for instance has its own utility cadastre platform since 1999 and has set up a governance framework with the corresponding utility providers. Québec and Rotterdam begin to register underground objects for land administration as well. A reliable 3D digital map of utility networks is crucial for urban planners to understand the impactful aspects of the underground space. In order to provide the accurate information of underground utility, Singapore Land Authority (SLA) and the Singapore-ETH Centre started the Digital Underground project to developing a roadmap for a reliable map of subsurface utilities in Singapore since 2017. Through an in-depth studying and analysis about the current states of underground utility in the world and the requirement of Singapore, together with hands-on case studies using well-known data capturing technology (i.e. Ground Penetrating Radar) and research on the 3D modelling of subsurface utilities. It can be observed that the various pieces of information that would constitute the data model exist in the data management systems of different stakeholders in Singapore. Utility networks information is managed by utility owners, land administration information is managed by Singapore Land Authority (SLA). While survey and quality metadata are currently not managed and consistently provided by utility owners. Therefore, this work focuses on the design of 3D underground utility data model and how the data model is connected to land administration based on Land Administration Domain Model (LADM). This case study attempts to explore methods for the integration of newly collected 3D data using underground mapping technology, existing planning 2D utility data and 2D cadastre data. Based on this is a primary study of underground utility in land administration, the data model can be evaluated and improved to establish a national mapping of underground utilities in Singapore.