Lack of complete information is the major factor causing accidents on metro tunnel projects. Safety risk control requires a comprehensive analysis of instrumentation data integrated with other safety related data. Based on a multidimensional data model, a safety-oriented geotechnical instrumentation data warehouse is established to integrate all the data from heterogeneous data sources, not only for quick retrieval of information on site, but also for further analysis. As one of the most important safety indicators, ground settlement is analyzed to take advantage of the data warehouse. A double Gaussian model is proposed to represent the settlement trough over twin tunnels. Moreover, a revised trough width parameter is proposed to represent the scope of safety risk areas. The ground loss is found to grow in a pattern that can be represented by a logistic curve. The first derivative of ground loss is applied to represent the evolution of safety risk.