The main reasons for rock masses to frequently exhibit impressive degrees of anisotropy, with properties varying with direction of observation and measurement, are clearly their varied geological origins. Origins may provide distinctive bedding cycles in sedimentary rocks, distinctive flows and flow-tops in basalts, foliation in gneisses, schistosity in schists and cleavage in slates, and faults through all the above. We can add igneous dykes, weathered horizons, and dominant joint sets. Each of the latter are rich potential or inevitable sources of velocity, modulus, strength and permeability anisotropy. The historic and present-day stress anisotropy provides a wealth of additional examples, which further reinforce disbelief in the elastic-isotropic-continuum intact-rock-based assumptions used and promoted by so many of us for modelling rock masses. RQD and Q are frequently anisotropic as well. Has the a priori assumption of homogeneous-isotropic-elastic behaviour any significant place in the scientific practice of rock mechanics?

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