Characterization and DEM Modeling of Shear Zones at a Large Dam Foundation
Publication: International Journal of Geomechanics
Volume 12, Issue 6
Abstract
Cataclastic rocks and fault gouge present highly variable properties, from those of soil-like materials to those of competent rock mass. In most cases, the entire rock mass, or internal major shear zones, can be represented as a block-in-matrix rock (bimrock), i.e., rock fragments of different shape and size, embedded in a finer matrix. In this paper, a tectonized metamorphic rock mass at the site of a planned gravity dam is investigated. The dam foundation is crossed by numerous major discontinuities, often grouped to form wider shear zones and characterized by high persistency, waviness, and abundant cataclastic filling. Systematic measurements of local orientation and filling thickness along the discontinuity traces made a detailed morphological analysis possible. The most frequent type of filling is a lightly cemented matrix-supported gouge. Undisturbed sampling of filling materials was successful only in some special cases. Laboratory tests, as well as in-situ mechanical tests, were therefore difficult and not exhaustive. Micromechanical distinct-element method (DEM) modeling was instrumental in obtaining a more comprehensive framework of deformation and failure mechanisms of cataclastic materials. The mechanical properties of the particulate model were first analyzed by numerical simulation of biaxial and direct shear tests. The relationship between the overall constitutive parameters and micromechanical properties, such as interparticle friction, contact stiffness, cement bond strength, volumetric block proportion, and block shape, was determined. The complex interplay between the geometric features of a major discontinuity (joint-wall roughness and waviness) and the properties of the infilling bimrock was then investigated, and finally, the overall strength of the infilled discontinuity was analyzed.
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Acknowledgments
The authors are grateful to Stefano Zanchetta and Francesco Micheli, who carried out most of the geological surveys, to Anita Di Giulio for her valuable support in carrying out activities on the site and in the laboratory, to Carlo Bartolucci for his help in the field activities, and finally to Paolo Tommasi, who is involved in the research program.
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Published In
International Journal of Geomechanics
Volume 12 • Issue 6 • December 2012
Pages: 648 - 664
Copyright
© 2012 American Society of Civil Engineers.
History
Received: Sep 9, 2011
Accepted: Apr 4, 2012
Published online: Apr 11, 2012
Published in print: Dec 1, 2012
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