Keywords: embankments, seismic design, slope stability, fault rupture, deformations.

Seismic design of any type of large-scale infrastructure consists of the evaluation of its performance due to seismic wave propagation (inertia response) and to permanent ground deformations, for example, due to an abrupt fault rupture [1,2]. Regarding the effects of fault rupture, seismic norms provide guidelines that are mainly related to the location of the geostructures. However, in major earth structures (such as dams, earth-filled embankments, landfills, etc) the additional distress imposed to them by the applied permanent deformations produced during a fault dislocation may be significant. In addition, other location related criteria (socio-economical, environmental, etc) may impose the requirement that a large-scale infrastructure (such as an earth dam) is constructed even in the vicinity of an active fault. In such cases, the consequences of the unavoidable permanent deformations should be carefully and realistically evaluated.

The current study includes a numerical investigation using elaborate finite element analyses of the distress of earth structures, focusing on the development of permanent deformations during the fault rupture propagation. The material nonlinearity is taken into account using the Mohr-Coulomb criterion with a strain softening behaviour. Initially, the numerical procedure is verified by comparing quantitatively the results obtained with the corresponding results from field cases, experiments and numerical studies reported in the literature. Subsequently, a parametric study is performed, in which the main parameters examined are the mechanic behaviour of the soil material, the fault type, the dip angle and the magnitude of displacement. In addition, the effect of the two-dimensional geometry of the geostructure in the resulting distress is evaluated, since another important aspect of the problem is the location of the fault tip, with respect to the slopes of the embankment.

The results indicate that significant ground surface deformations may develop due to the fault displacement. More specifically, a higher magnitude of base fault slippage is required for a reverse fault than for a normal one, to propagate through the embankment and reach the ground surface. Additionally, the ground surface deformation exhibits a more smooth variation for reverse faults, while in normal faults a scarp, or even a graben at lower dip angles, is developed. By comparing one-dimensional and two-dimensional models, reverse faults seem to be influenced by the slopes of the geostructure, since the deformations obtained in the two-dimensional model increase as the failure surface approaches the crest. It was also found that reverse faults propagate with greater inclination, approaching vertical orientation, when the fault tip is located under the slopes of the earth structure. By contrast, normal faults may propagate with the same inclination regardless of the position of the fault tip, but when the fault dislocates under the slope then a wider zone of marginally lower magnitude plastic strains is developed at the surface. Conclusively, the aforementioned results imply that geotechnical seismic design should assess very thoroughly the behaviour of an earth structure resulting from a nearby fault displacement.

1

Bray J.D., Seed R.B., Cluff L.S., Seed H.B., "Earthquake fault rupture propagation through soil", Journal of Geotechnical Engineering, 120(3), 543-561, 1994. doi:10.1061/(ASCE)0733-9410(1994)120:3(543)

2

Cole D.A., Lade P.V., "Influence zones in alluvium over dip-slip faults", Journal of Geotechnical Engineering, 110(5), 599-615, 1984. doi:10.1061/(ASCE)0733-9410(1984)110:5(599)

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