Estimating in-situ stresses for the selection of the alignment of unlined pressure tunnels

In this paper, it is shown how analytical solutions, proposed recently by the authors for predicting in-situ stresses in rock masses with smooth and irregular topographies, can help in the selection of the alignment of unlined pressure tunnels near slopes and valley walls. The proposed methodology can be applied to ridges and valleys in isotropic or anisotropic rock masses subject to gravity or to combined gravitational and tectonic loading. It is found that the safe alignment of unlined pressure tunnels depends greatly on the extent of tensile regions in valley walls, which itself depends on the valley geometry, the degree of rock anisotropy, the orientation of the planes of rock anisotropy and the in-situ loading conditions.