Pressure tunnels in non-uniform in situ stress conditions

The bearing capacity of prestressed concrete-lined pressure tunnels is governed by the in situ stress of rock mass, which generally has different magnitudes in the vertical and horizontal direction. Two cases were distinguished, based on whether the vertical stress is greater than the horizontal stress or not.By means of a finite element model (FEM), the resulting distribution of stresses, strains and deformations due to tunnelling processes was revealed. The bearing capacity of pressure tunnels was determined based on the superposition principle. The results obtained demonstrate the significance of horizontal-to-vertical stress coefficients in the bearing capacity of pressure tunnels prestressed by grouting. Favourite locations where crack openings in the final lining may occur are identified, which is useful for taking measures regarding the tunnel tightness and stability.