ABSTRACT
Over the last decade or so, new concepts and techniques have been developed to conduct geotechnical exploration, related to tunnel construction, using the technology of directional drilled borings (DDB) (Lindhjem 2009, Howard et. al. 2005, Gui et.al. 2002). These new techniques have been made possible by significant advances in the directional drilling industry, particularly with respect to improved guidance and location control. These developments have allowed long, continuous geotechnical explorations along tunnel alignments in rock. For the soft ground (soil) tunnels, the extensive use of compensation grouting to minimize ground movements of structures during tunnel construction has driven new demands for better control of the location of DDBs. New techniques are being developed to carefully monitor and interpret parameters measured during the drilling process itself as input to the type and nature of the ground being encountered (Osbak 2011). Existing geophysical techniques have also been adapted to DDB to investigate for obstructions such as boulders, piles, steel casings, and so forth. These new developments suggest that DDB can and should be developed further using the above-mentioned techniques to provide continuous geotechnical information along tunnel alignments.
