ABSTRACT:
A combined geological and rock mechanics approach to tunnel face behaviour prediction, based on improved understanding of brittle fracture processes during TBM excavation, was developed to complement empirical design and performance prediction for TBM tunnelling applications in novel geological conditions. A major challenge of this research is combining geological and engineering languages, methods, and objectives to construct a unified geomechanics characterisation system. The goal of this system is to describe the spalling sensitivity of hard, massive, highly stressed crystalline rock, often deformed by tectonic processes. Geological, lab strength testing and TBM machine data were used to quantify the impact of interrelated geological factors, such as mineralogy, grain size, fabric and the heterogeneity of all these factors at micro and macro scale, on spalling sensitivity and to combine these factors within a TBM advance framework. This was achieved by incorporating aspects of geology, tectonics, mineralogy, materials strength theory, fracture process theory and induced stresses.
1 INTRODUCTION
Tunnel Boring Machines (TBM) are being used for tunnel excavation in deeper and tougher environments than ever before. Current TBM design and performance prediction methods based on empirical databases and lab scale and in-situ testing (Bruland 1998, Rostami et al. 2002, Rostami et al. 1996, Zhang et al. 2003) consider factors such as UCS, Brazilian tensile strength, joint characteristics (Barton 2000, Sapigni et al. 2002) and TBM specific index test values (CERCHAR 1986, Dollinger et al. 1999, Plinninger et al. 2003). These design methodologies can be successfuly applied to projects that fit within the realm for which the empirical databases contain a large amount of data. When attempting to apply these methodologies to novel conditions, such as in very hard, massive or foliated, unjointed rock at high stress, the nuances that are important under these conditions may be overlooked during TBM design.
