The use of monitoring data and geological documentation as a basis for defining rock mass behavior types for tunnelling

The use of geodetic surveying to measure the absolute 3-D tunnel displacements has provided new opportunities to evaluate the system behavior and interpret the rock mass behavior associated with tunneling. For a meaningful case history evaluation it is necessary to have consistent and quality documentation covering the excavation and support sequence, the geological conditions, as well as the displacement measurements. Combing this data allows the rock mass behavior type to be evaluated. In contrast to many available rock mass characterization or classification procedures, the procedure introduced by the Austrian Society for Geomechanics within the Guideline for
the Design and Construction of Conventional Tunnels, focuses on site specific evaluations of the rock mass types, potential rock mass behavior types considering the system boundary conditions and influencing factors, then determines the potential system behavior for different excavation and support methods. Using case histories provides valuable opportunities to develop a data base on rock mass behavior types associated with different environments and excavation and support systems. The examples discussed in this paper demonstrate this procedure can be used to identify key geologic parameters and associated behavior types.