This paper deals with two forms of preconditioner which can be easily used with a Conjugate Gradient solver to replace a direct solution subroutine in a traditional engineering ÿnite element package; they are tested in such a package (FINAL) over a range of 2-D and 3-D elasticity problems from geotechnical engineering. Quadratic basis functions are used.A number of modiÿcations to the basic Incomplete Choleski [IC(0)] factorization preconditioner are considered. An algorithm to reduce positive o -diagonal entries is shown in numerical experiments to ensure stability, but at the expense of slow convergence. An alternative algorithm of Jennings and Malik is more successful, and a relaxation parameter ! is introduced which can make a further signiÿcant improvement in performance while maintaining stability. A heuristic for determining a near-optimal value of ! is proposed. A second form of preconditioning, symmetrically scaled element by element, due to Bartelt, is also shown to perform robustly over a range of problems; it does not require assembly of the global sti ness matrix, and has great potential for parallelization. ? 1997 by John Wiley & Sons, Ltd.
Path dependent and time-dependent constitutive models and experience with their use for numerical simulation of field performance of concrete and rockfill dams are described in the paper. For the mechanical part of the solutions, a combined model using path dependent incrementaly-linear elasticity in the pre-peak regime and theory of plasticity in the peak regime is applied. Using proper switch functions and path dependent relations for calculating tangent values of the conventional deformational characteristics, the function of double hardening elastic-plastic models is approximated. For the time dependent part of the solutions, the theory of multiface viscoplasticity with two and three viscoplastic surfaces is applied. The two-surface model allowed simulating the observed viscoplastic flow of weak marly shale in foundation of a concrete dam displaying unusual behaviour. Viscoplastic flow with three surfaces was successfully applied for modelling long-term creep of rockfill. This model and its application for Sance Rockfill Dam are described in more detail.
Safety assessment of the 62 m high Sance Rockfill Dam based on long-term monitoring results and their simulation by numerical models is presented in the paper. Unexpectedly large settlements and horizontal movements of the crest together with the steep downstream slope questioned the safety of the dam. Calibrated 2D and 3D models fitting the monitoring results were applied for the safety assessment of the dam including slope stability analysis and estimation of the clay core cracking and hydraulic fracturing hazard. The modeling results contributed to the rehabilitation concept and project of the dam. Fig. 1 Sance drinking water reservoir-key source of drinking water for Moravian-Silesian region Front.
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