A parameter study of the damaged rock zone around shallow tunnels in brittle rock

As part of an ongoing study on the mechanical characteristics of the damaged rock zone (DRZ) around underground excavations and its influence on the overall performance of the excavation, a parameter study was carried out using the continuum method of numerical analysis. This assisted in identifying the sensitivity of the parameters tested, thereby laying the groundwork for further numerical investigation. The main parameters investigated include the extent of DRZ, the strength and stiffness of DRZ, and the depth of the excavation. The main quantity used to test the sensitivity of these parameters is the response of induced stresses around the excavation boundary resulting from the variation in these parameters. In the study presented in this paper, typical in-situ stress and rock mass conditions observed for shallow tunnelling projects in Sweden are used. The results clearly demonstrate the effect of DRZ on the excavation as well as the criticality of various parameter combinations. The strength of DRZ although sensitive, is the most complex to define and the tool used in this study to determine the empirical plastic strength components, namely cohesion and friction, is felt to be uncertain.Godkänd; 2006; 20071004 (davsai