HR: 1330h
AN: H42F-1142    [PDF]
TI: Multi-scale characterization of rock fracture surfaces using roughness analysis and geostatistics
AU: Grasselli, G
EM: ggrasse@sandia.gov
AF: Geophysical Technology Department, Sandia National Laboratories, PO Box 5800 MS0750, Albuquerque, NM 87185-0750 United States
AU: * Saito, H
EM: hsaito@sandia.gov
AF: Geohydrology Department, Sandia National Laboratories, PO Box 5800 MS0735, Albuquerque, NM 87185-0735 United States
AB: Surface roughness is a major factor in the determination of strength, deformability and fluid flow properties of rock joints. The surface roughness coupled with stresses that act on the fracture plane determine the geometry of the contacts and void distribution. Therefore, in the evaluation of the hydro-mechanical behavior of a rock fracture it is necessary to consider the contribution of the roughness. Experimental flow tests show that with increasing shear displacement, the fracture becomes heterogeneous, anisotropic, and more permeable in the direction perpendicular to the displacement. On the other hand, dry shear tests show that the surface fails in areas facing the shear direction. The empirical description of the surface proposed by Grasselli can be extended to all possible directions, resulting in a polar diagram that represents the directional distribution of the roughness over the surface (the roughness rose). The ability of this method has been shown to not only illustrate the differences in roughness, but, coupled to the shear tests results, also to quantify its contribution to the shear strength. In this paper, the method proposed by Grasselli for quantifying the roughness is compared to a geostatistical approach that has been developed to analyze and process spatially distributed observations. The semivariogram allows for the analysis of the spatial variability of surface roughness in a given orientation, providing a model that describes the statistical features of the surface. Two different surfaces, one with a strong anisotropic roughness, and the other almost isotropic, have been analyzed with the two methods. Both methods are able to capture the major geometric feature of the surfaces, with a good agreement of the findings. The results constitute the base-case for trying to couple the two discussed methodologies, in order to create a multi-scale methodology for the quantification of the roughness. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
DE: 5104 Fracture and flow
DE: 5112 Microstructure
DE: 8010 Fractures and faults
SC: Hydrology [H]
MN: 2003 Fall Meeting