HYBRID DESIGN ROCK SUPPORT | GROUND SUPPORT
Above, figure 2: Buckling failure of RRS-support in the new Skarvberg tunnel chainage 3 + 162 PHOTO CREDIT: SKANSKA NORGE AS The design of permanent rock support also turns
more challenging. Some examples have been addressed by authors like Perras and Diederichs (2009) and Diederichs (2020) from case studies in Canada and Australia, respectively. Similar cases with tunnel stability problems and/or design challenges have been also found in Norwegian tunnels, such as the North Cape tunnel in which unforeseen and significant roof stability problems, over long tunnel sections, resulted in high support consumption (Melby et al. 2002; Palmstrom, personal communication 2023). The recent construction of the new Skarvberg tunnel showed extensive sections with roof overbreak, delamination problems, and a tunnel failure, resulting in a significant increase of the required rock support (Bøgeberg and Skretting 2021; Gildestad and Bakkevold 2021). Some of the challenges can be attributed to
limitations of current design methods, such as empirical classification systems being unable to capture and describe the basic ground properties controlling the anisotropic ground behaviour of layered rocks. As noted
by authors like Palmstrom and Broch (2006), Palmstrom and Stille (2006), Marinos et al. (2005), Anagnostou and Pimentel (2009), Palmstrom (2009), Vibert and Vaskou (2011), Høien et al. (2019), and Terron-Almenara and Li (2023), the well-established and widely used classification systems are built upon the assumption of structural isotropy; these include the Rock Mass Rating (RMR) of Beniawski (1973; 1989), the Q-system (Barton et al. 1974; NGI 2015), and the Geological Strength Index (GSI) of Hoek (1994). Alternatively, analytical solutions based on the
Voussoir beam analogue of jointed rock roofs may be also used to evaluate the roof stability of an excavation, as suggested in Sofianos (1996) and Diederichs and Kaiser (1999), among others. However, such an approach also presents limitations in predicting roof stability due to challenges for some of the mentioned analytical solutions to simulate tunnel shape and jointing, the effect of in-situ stresses and rock support, and also the failure mechanisms of the beds (Oliveira and Pells 2014; Bakun-Mazor et al. 2009; Abousleiman et al. 2021, 2023).
Above, figure 3: Interaction between layered ground, ground reinforcement at the tunnel face with radial bolts (dark brown colour) and ahead of the face with bolt spiles (grey color), and Si-RRS arches. a Longitudinal section. b Cross section (tunnel span ~ 10m)
September 2025 | 17
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45
