ABSTRACT
Since a rock mass generally contains joints and microcracks, which are both a source of water and compliant, the application or existence of an anisotropic (effective) stress distribution may preferentially have closed those oriented at an obtuse angle to the major stress, while keeping those at acute angles or sub-parallel to the major stress, ‘open’. There are then grounds for expecting both anisotropic permeability tensors, and a corresponding anisotropic velocity, with both maxima tending to be parallel or sub-parallel to the major stress. Since subvertical jointing may dominate in the same way that horizontal stress anisotropy may dominate, the anisotropy will tend to be related to azimuth. However, there is a potential source of error here. The permeability test holes must intersect the ‘open’ structure to register their higher permeability. The test holes needs to be drilled in the ‘slow’ direction, parallel to the minimum stress. The lower Q-value given by crossing all the ‘open’ joints, should correspond to the higher permeability.
