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Allowing the transitory attainment of bearing capacity of caisson foundations supporting bridge piers during strong seismic events can lead to substantial optimisation in their design and major cost savings. If the approach of capacity design is applied to geotechnical systems, the temporary triggering of plastic mechanisms may be permitted if the resulting permanent displacements are smaller than given threshold values. To validate this design approach, the seismic performance of caisson foundations was assessed through dynamic centrifuge testing on reduced-scale models. This paper presents the results of two tests in which a caisson–pier–deck system was embedded in a typical alluvial deposit and subjected to a series of earthquakes of different intensities. The caissons were founded on soft and very soft clay, to either avoid or induce the attainment of plastic soil behaviour under the same seismic inputs. It is shown that both yielding and failure of the layer of very soft clay limit inertial forces transmitted to the superstructure, validating the design approach and some useful empirical relations available in the literature. In contrast, inelastic soil behaviour implies accumulation of permanent rotation and settlement of the system, which must be carefully evaluated to check for fulfilment of performance requirements. [ABSTRACT FROM AUTHOR]

Seismically induced landslides can often cause severe human and economic losses. Therefore, it is worth assessing the seismic performance of slopes through a reliable quantification of the permanent displacements induced by seismic loading. This paper presents a new semiempirical relationship linking the permanent earthquake-induced displacements of slopes to one or two synthetic ground motion parameters developed considering the Italian seismicity, and a comparison with existing simplified displacement models is illustrated. Once combined with a fully probabilistic approach, these relationships provide a useful tool for practicing engineers and national agencies for a preliminary estimate of the seismic performance of a slope. In this perspective, the predictive capability of different semiempirical relationships is analyzed with reference to the permanent displacements evaluated for the Italian seismicity assimilating the slope to a rigid body and adopting the Newmark integration approach. The consequences of the adoption of these relationships on the results of the probabilistic approach are illustrated in terms of displacement hazard curves and hazard maps for different slope scenarios. [ABSTRACT FROM AUTHOR]

The seismic performance of earth dams can nowadays be performed via dynamic analyses using constitutive models of sufficient accuracy in describing cyclic soil behavior. However, a number of assumptions different from soil model affect the problem as a whole. In this paper, a 2D model of a simplified homogeneous earth dam is developed, to assess the influence of bedrock compliance, vertical component of ground motion, stabilizing berms, and initial pore water pressure distribution on its seismic performance, thus providing some guidance on the choices that should be adopted for a safe assessment of the seismic performance of existing earth dams. [ABSTRACT FROM AUTHOR]

Substructure method is widely used to evaluate the seismic performance of caisson foundations supporting bridge piers subjected to strong ground motions, mainly because of its simplicity. However, the strongly‐simplifying assumption of linear viscous‐elastic behaviour for the foundation soil limits its applicability to flexible systems subjected to low‐intensity earthquakes, for which irreversible strains and pore water pressure build‐up are not anticipated. Furthermore, lumped‐parameter models are typically adopted in calculations in which soil‐foundation compliance is reproduced via dynamic impedance functions, whose dependency on frequency of excitation is often neglected. Modification of free‐field motion leading to foundation input motion (FIM), due to the presence of caisson embedment, is also mostly ignored. The influence of these simplifying assumptions on the seismic performance of bridge piers on caisson foundations is assessed in this paper through a parametric study, where soil‐caisson‐bridge pier‐deck systems differing in geometric and mechanical properties are subjected to real seismic records. Dynamic analyses were carried out in the time domain with the finite element method, using a 3D continuum and a lumped‐parameter model for the foundation soil. In the 3D model both the linear viscous‐elastic and the nonlinear soil behaviour were assumed, while linear viscous‐elastic behaviour was assumed in the lumped‐parameter model. The influence of inelastic soil behaviour was assessed by comparing the seismic performance of the systems obtained with the 3D model, while the role of FIM was evaluated by comparing the results of the dynamic analyses computed assimilating the soil to a linear elastic medium. [ABSTRACT FROM AUTHOR]

In the last decades, Italy has experienced several strong earthquakes, triggering the attention on the high seismic risk associated with the potential instability of large existing earth dams. Under intense seismic events, dam response depends on various factors including the geometry and the type of water retention scheme. This paper explores the influence of these factors, comparing the seismic performance of two idealized earth dams: a homogeneous dam and a zoned dam. The simplified models adopted in the analyses are representative of these two classes of earth dams, often adopted in the sixties to design various dams located in southern Italy. The idealized models, here examined in detail, have comparable heights and foundation soil conditions, differing in terms of water retention scheme. The seismic response of the dams was evaluated through time‐domain nonlinear dynamic analyses in which the same input ground motion, represented by real‐time histories, was applied at the base of the models. It is shown that for highly inelastic systems, such as those at hand, duration of input motion should be accounted for in addition to compatibility criteria with a design elastic response spectrum. Also, different slopes of dam flanks, shear strength mobilization at the end of dam construction and high stiffness contrast at the shells‐core contacts are shown to result in different deformation patterns at the end of earthquake loading. Some peculiarities in the behavior of these classes of earth dams are highlighted in the paper, providing a guidance for the rational assessment of their seismic performance. [ABSTRACT FROM AUTHOR]