- Email: [email protected]
Characterization of phyllites for tunnelling
ARTICLE IN PRESS
International Journal of Rock Mechanics & Mining Sciences 41 (2004) 396
SINOROCK2004 Paper 1B 05
Characterization of phyllites for tunnelling E.A. Button Graz University of Technology, Institute for Rock Mechanics and Tunnelling, Rechbauerstrasse 12, Graz 8010, Austria
Abstract Rock mass characterization and the development of a geotechnical model form the basis for tunnel design. Many characterization procedures focus on determining the engineering parameters necessary for empirical or numerical evaluations of the required tunnel support, but this is only one step in the characterization process. The Guideline for the Geomechanical Design of Conventional Tunnels recently introduced by the Austrian Society for Geomechanics (2001), focuses on characterizing the rock mass behaviour and potential failure mechanisms considering the site specific influencing factors and boundary conditions. Case histories from tunnels in phyllites in which systematic, 3D absolute displacement monitoring was carried out have been used to identify the influence of the rock mass structure and the rock mass quality on the system behaviour. Basic key parameters for phyllitic and similar metamorphic rock masses are the anisotropic strength and deformability associated with the foliation, foliation orientation persistence, fault and joint characteristics, mineralogy (per cent and distribution of phylosilicates and clay minerals). To develop rock mass behaviour types, which consider the full excavation area without any support, the following influencing factors should be considered; relative orientation of foliation to the excavation, fault orientation and spatial characteristics, stress level, ground water, excavation size and shape. It is also important to recognize the potential for initiating global slope movements especially in portal regions or hill slope tunnels. Owing to the variability both in rock mass quality and spatial distributions rock mass behaviour types must be determined based on scenarios developed from the geologic model. These scenarios should be treated probabilistically during the design phase and used during the excavation to assist in interpreting monitoring results. The observed rock mass behaviour is highly influenced by the local spatial relations between influencing structures and the excavation. Therefore, only with a comprehensive understanding of both the geologic conditions and geomechanics can reliable evaluations of the rock mass and behaviour be made (Fig. 1). Keywords: Phyllites; Characterization; Rock mass behaviour; Tunnelling; Squeezing ground
Fig. 1. Example of monitored displacements and the associated geologic conditions used for evaluating rock mass behaviour characteristics of phyllites. E-mail address: [email protected] (E.A. Button). For full length paper see CD-ROM attached. doi:10.1016/j.ijrmms.2003.12.053
International Journal of Rock Mechanics & Mining Sciences 41 (2004) 396
SINOROCK2004 Paper 1B 05
Characterization of phyllites for tunnelling E.A. Button Graz University of Technology, Institute for Rock Mechanics and Tunnelling, Rechbauerstrasse 12, Graz 8010, Austria
Abstract Rock mass characterization and the development of a geotechnical model form the basis for tunnel design. Many characterization procedures focus on determining the engineering parameters necessary for empirical or numerical evaluations of the required tunnel support, but this is only one step in the characterization process. The Guideline for the Geomechanical Design of Conventional Tunnels recently introduced by the Austrian Society for Geomechanics (2001), focuses on characterizing the rock mass behaviour and potential failure mechanisms considering the site specific influencing factors and boundary conditions. Case histories from tunnels in phyllites in which systematic, 3D absolute displacement monitoring was carried out have been used to identify the influence of the rock mass structure and the rock mass quality on the system behaviour. Basic key parameters for phyllitic and similar metamorphic rock masses are the anisotropic strength and deformability associated with the foliation, foliation orientation persistence, fault and joint characteristics, mineralogy (per cent and distribution of phylosilicates and clay minerals). To develop rock mass behaviour types, which consider the full excavation area without any support, the following influencing factors should be considered; relative orientation of foliation to the excavation, fault orientation and spatial characteristics, stress level, ground water, excavation size and shape. It is also important to recognize the potential for initiating global slope movements especially in portal regions or hill slope tunnels. Owing to the variability both in rock mass quality and spatial distributions rock mass behaviour types must be determined based on scenarios developed from the geologic model. These scenarios should be treated probabilistically during the design phase and used during the excavation to assist in interpreting monitoring results. The observed rock mass behaviour is highly influenced by the local spatial relations between influencing structures and the excavation. Therefore, only with a comprehensive understanding of both the geologic conditions and geomechanics can reliable evaluations of the rock mass and behaviour be made (Fig. 1). Keywords: Phyllites; Characterization; Rock mass behaviour; Tunnelling; Squeezing ground
Fig. 1. Example of monitored displacements and the associated geologic conditions used for evaluating rock mass behaviour characteristics of phyllites. E-mail address: [email protected] (E.A. Button). For full length paper see CD-ROM attached. doi:10.1016/j.ijrmms.2003.12.053