Wannenmacher, H, Entfellner, M, Kalenchuk, K, Oke, J, Fiest, T & Perras, MA 2024, 'Ductile shotcrete linings: A potential solution for mining in overstressed weak rocks?', in P Andrieux & D Cumming-Potvin (eds), Deep Mining 2024: Proceedings of the 10th International Conference on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth, pp. 563-574, https://doi.org/10.36487/ACG_repo/2465_33
(https://papers.acg.uwa.edu.au/p/2465_33_Entfellner/)
Abstract: Mining and tunnelling in overstressed weak rocks can result in substantial and long-lasting deformations, often referred to as ‘squeezing ground conditions’. The magnitude of deformations is closely tied to the rock mass competency and stress conditions, as well as the applied excavation and support concept and can reach tens or even hundreds of centimetres in very weak rock conditions.
The direct relation between rock pressure and deformation, represented by the ground reaction curve, suggests applying the yielding principle. The yielding principle states that the support capacity requirement decreases as deformation increases. To enable controlled deformation and safe working conditions, yielding elements as a part of the shotcrete lining are implemented. These elements avoid overstressing the shotcrete lining even at large and long-lasting creep displacements. During the deformation process, the support pressure of the yielding elements and liner increases, thus stabilising the rock mass. This economic support technique represents the state-of-the-art infrastructure tunnelling practice in overstressed weak rocks. A novel yielding element of high-strength expanded polystyrene has been invented, which overcomes existing systems’ drawbacks. Recent experiences from applications in Alpine base tunnels are presented. This deformation-based support system may be an economical solution in mining for permanent structures with large deformations and required long-term stability.

Keywords: deep mining, tunnelling, ground support, ductile lining, shotcrete, squeezing ground, overstressed weak rock, yielding elements, NATM, HS-EPS