Hydromechanical Analysis of Masonry Gravity Dams and their Foundations
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ORIGINAL PAPER
Hydromechanical Analysis of Masonry Gravity Dams and their Foundations Eduardo M. Bretas • Jose´ V. Lemos Paulo B. Lourenc¸o
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Received: 19 June 2012 / Accepted: 21 August 2012 / Published online: 7 September 2012 Ó Springer-Verlag 2012
Abstract A numerical model for the hydromechanical analysis of masonry dams based on the discrete element method is presented. The dam and the rock foundation are represented as block assemblies, and a coupled flow-stress analysis is performed in an integrated manner for the entire system. Complex block shapes may be obtained by assembling elementary blocks into macroblocks, allowing the application of the model to situations ranging from equivalent continuum to fully discontinuum analysis. A contact formulation was developed based on an accurate edge–edge approach, incorporating mechanical and hydraulic behavior. The main numerical aspects are described, with an emphasis in the flow analysis explicit algorithm. An application to an existing masonry dam is presented, analyzing its present condition, with excessive seepage, and the proposed rehabilitation intervention. An evaluation of sliding failure mechanisms was also performed, showing the expected improvement in the safety of the structure. Keywords Masonry dams Discrete elements Hydromechanical analysis Failure
E. M. Bretas (&) J. V. Lemos National Laboratory for Civil Engineering, Av. do Brasil, 101, 1700-066, Lisbon, Portugal e-mail: [email protected] J. V. Lemos e-mail: [email protected] P. B. Lourenc¸o Department of Civil Engineering, ISISE, University of Minho, Guimara˜es, Portugal e-mail: [email protected]
1 Introduction Seepage, which takes place through the whole dam-foundation system, is a much relevant phenomenon when assessing the structural safety of dams, particularly in the case of gravity dams. The flow is established primarily in the discontinuities, being almost negligible through the concrete or rock, due to the low permeability of these materials. In the particular case of masonry gravity dams, water flow may occur in the dam body (in cracks or other discontinuities), in the dam–rock interface and through the foundation itself. There were several accidents directly related to this phenomenon, such as the historical accident of Bouzey dam, in 1895, which brought attention to the role of water pressure in dam safety (Bretas et al. 2012). Seepage is a consequence of the hydraulic gradient imposed by the dam and for this reason cannot be avoided. It is therefore necessary to adopt control measures, such as the grout curtains and the drainage systems. The intensity of the seepage and its effect on the safety of the structure depend fundamentally on the characteristics of the water reservoir, the flow velocity and the stress field established due to the presence of water (ICOLD 1983). The reservoir water may be too aggressive for mortar and concrete and may thus lead to a progressive degradation of the material by leaching the calcium (Eglinton 1987). This phenomenon is even more evident in
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