This paper discusses the behaviour of large-span tunnels and caverns in hard rock in a major underground storage project. In-situ stresses were measured using hydraulic fracturing during site investigation and 3-D overcoring during construction, with both showing a horizontal stress ratio of 2-3 times the vertical stress. Rock reinforcement design was based on the Q-system combined with numerical modelling for special design cases. Tunnel design and performance were checked and monitored by in-situ instrumentation during rock excavation, including measurements of deformation, convergence, and load on rock bolts. Deformation measurements using borehole extensometers included one borehole drilled into the virgin rock before rock excavation, which provided a direct and very insightful comparison with the various deformation measurements made during rock excavation. These measurements coupled with numerical calculations have proven that the high horizontal stresses to be very favourable to the stability of the large openings.
|Number of pages||6|
|Publication status||Published - 1 Jan 2003|
|Event||10th International Society for Rock Mechanics Congress, ISRM 2003 - Sandton, South Africa|
Duration: 8 Sep 2003 → 12 Sep 2003
|Conference||10th International Society for Rock Mechanics Congress, ISRM 2003|
|Period||8/09/03 → 12/09/03|