This paper presents the mechanical and hydraulic behaviour of passively prestressed concrete-lined pressure tunnels embedded in elastic transversely isotropic rocks subjected to non-uniform in situ stresses. Two cases are distinguished based on whether the in situ vertical stress in the rock mass is higher, or lower than the in situ horizontal stress. A two-dimensional finite element model was used to study the influence of dip angle, α, and horizontal-to-vertical stress ratio, k, on the bearing capacity of prestressed concrete-lined pressure tunnels. The study reveals that the in situ stress ratio and the orientation of stratifications in the rock mass significantly affect the load sharing between the rock mass and the lining. The distribution of stresses and deformations as a result of tunnel construction processes exhibits a symmetrical pattern for tunnels embedded in a rock mass with either horizontal or vertical stratification planes, whereas it demonstrates an unsymmetrical pattern for tunnels embedded in a rock mass with inclined stratification planes. The results obtained for a specific value α with coefficient k are identical to that for α + 90° with coefficient 1/k by rotating the tunnel axis by 90°. The maximum internal water pressure was determined by offsetting the prestress-induced hoop strains at the final lining intrados against the seepage-induced hoop strains. As well as assessing the internal water pressure, this approach is capable of identifying potential locations where longitudinal cracks may occur in the final lining.

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Based on the non-linear finite element analysis, the maximum bearing capacity of a plain circular concrete lining subjected to external and internal pressure is investigated. Numerical results regarding elastic stresses and deformations are compared with those calculated using the classical thick-walled cylinder theory. Referring to the discrete cracking concept and assuming that the concrete behaves as a brittle material, the redistribution of stresses after cracks have occurred is further investigated. The normal tensile strength in the lining will reduce to zero as soon as the joint element is cracked. These analyses confirm that the proposed modelling method may be used satisfactorily, to model the cracking process of passive pre-stressed circular concrete linings.@en