Study on permeability and hydrodynamic dispersion in jointed rock

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1) A theoretical as well as a numerical study has been carried out with special emphasis on developing a basic under-standing of how crack geometry influences hydraulic phenomena such as permeability and hydrodynamic dispersion in cracked bodies. The permeability tenser kappa_<ij> is formulated in terms of length. aperture and orientation of cracks plus one more non-dimensional scalar lambda depending on conneetivity among cracks. By extending the Robinson's formula, a general expression for lambda is given as a function of density and anisotropy of existing cracks. Dispersion tenser D_<ij> consists of two different sources. The first comes from the fact that each tracer is forced to move along cracks the directions of which deviate from the mean path. The second comes from non-uniform distribution of hydraulic head throughout a cracked body. The second source has increasing importance not only when crack density is low, but also when crack arrangement is highly anisotropic. The distribution of head becomes extremely non-uniform, especially when overall hydraulic head gradient is parallel to the preferred orientation of cracks.2) Rock structure can be qualitatively, as well as generally. described by using tensors. In order to show how such a tensor is useful for the description purpose of rock structure, a crack tensor is introduced as an index measure for the rock structure by joints and faults, and is discussed in detail to clarify the geometrical meaning. Four cylindrical specimens of granite, which are immersed in hot water of 90 for 0,180,1030 and 2000 days respectively, are examined to see if the crack tensors can be actually determined by purely microscopic observation. Using thus determined crack tensors for the granite specimens. permeability tensors are estimated in good agreement with experimentally determined permeability values.