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Abstract
A robust and efficient numerical tool has been developed to evaluate the behaviour of earth and rockfill dams during seismic loading and to determine the associated deformations. Realistic behaviour of earth materials can be simulated if the plastic response of the soil and rockfill is appropriately considered. This has been achieved by employing a bounding surface plasticity constitutive model in a large deformation finite difference analysis. A novel mapping rule has been introduced in this work to improve the efficiency and applicability of the model in simulation of complex stress paths, which are usually encountered in soil during highly variable seismic loading. The constitutive model has also been extended to include the behaviour of rockfills and highly crushable materials. To resolve the problems associated with the effects of overshooting in the solution of boundary value problems, a new concept has been introduced in this work and successfully implemented in the solution algorithm in order to avoid spurious unloading/reloading stress paths and their associated hardening effects. The validity of the proposed models and the efficiency of the numerical tool have been demonstrated through simulation of a series of triaxial laboratory tests as well as a number of case studies on a range of monotonic and cyclic loadings. These cases include settlement of a foundation, liquefaction of loose to medium granular soils in two centrifuge tests, and failure of the lower San Fernando Dam during the 1971 earthquake. The predicted behaviours were compared with either laboratory test data or field measurements and reasonable agreements were obtained in all cases. The numerical tool has been used to simulate the deformations of modern earth dams during earthquakes. The seismic behaviour of earthfill and rockfill dams has been simulated under a wide range of frequency contents. The reliability of the simplified methods, which are widely used in industry for seismic analysis of earth dams, has also been investigated and shown that these methods are not conservative for all cases, as widely presumed, and factors such as tuning ratio affects the reliability of the results of the simplified methods.