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  Parametric Study of Steel-Lined Pressure Shafts in Anisotropic Rock

  The development of high-capacity Pelton turbines and high-strength steel (HSS) allows the design of high-head power plants up to 2000m gross head to meet the increasing demand for peak energy [1]. With the rise of volatile new renewable energies, storage hydropower plants are subjected to more drastic operational requirements to balance the electricity grid. HSS has been developed to address the mechanical requirements, but they are more difficult to weld than ductile grades. Furthermore they are more sensitive to fatigue and brittle failure [2-3]. The common method for the design of steel-lined pressure tunnels and shafts considers an axisymmetrical model in isotropic rock to compute the stresses and deformations, taking the lowest elastic modulus measured in situ. Such an approach is commonly considered as conservative for the maximum stresses in the steel liner [4]. In Europe, the CECT (1980) recommendations [5] are followed for the design and the construction of steel-lined pressure tunnels and shafts. These guidelines are applicable for ductile steel grades, but are no longer adequate for the design with HSS. Instead, designers use a range of horizontal failure assessment methods and/or recommendations, but there is still a need for specific recommendations for steel-lined pressure shafts embedded in rock. Several authors have studied the behaviour of linings in anisotropic rock (e.g. [6-11]). However, the case of steel-lined pressure tunnels or shafts has not yet been studied systematically in anisotropic rock. There is neither analytical solution nor extensive parametrical study of these structures available in anisotropic rock. In this work, the behaviour of steel liners considering the anisotropic behaviour of the rock is studied by means of the FEM. The solution in isotropic rock is introduced in Section 2. The constitutive models are discussed in Section 3. Finally, the numerical model, the parametric study and the results are presented in Section 4.

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