Abstract
Joint effects on rock-mass anisotropy are examined by considering granodiorite and metasediment rock masses that were encountered in two different tunnelling projects. Composite moduli are determined using two simple models representing the constraints of equilibrium and compatibility. The equilibrium constraint gives a lower value modulus where there is no stress redistribution as the rock mass deforms. The compatibility constrained modulus characterises the stress distribution and redistribution as deformation occurs. Rock-mass moduli, and their dependance on joint orientation and imposed stress ratio environments, are examined. By considering rock masses encountered in two tunnelling projects it is shown that rock-mass anisotropy is not only very sensitive to joint characteristics and orientation but also to in-situ stresses. In a very poor (Class 5) metasedimentary rock mass, it is shown that in-situ stresses induce significant anisotropies whereas initially pseudo-isotropic elasticity was assumed because of the multiple jointing.
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