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Shallow embankment slopes are commonly used to support elements of transport infrastructure in seismic regions. In this paper, the seismic performance of such slopes in non-liquefiable granular soils is considered, focusing on permanent movement and dynamic motion at the crest, which would form key inputs into the aseismic design of supported infrastructure. In contrast to previous studies, the evolution of this behaviour under multiple sequential strong ground motions is studied through dynamic centrifuge, numerical (finite-element, FE) and analytical (sliding-block) modelling, the centrifuge tests being used to validate the two non-physical approaches. The FE models focus on the specification of model parameters for existing non-linear constitutive models using routine site investigation data, allowing them to be used routinely in design and analysis. Soil-specific constitutive parameters are derived from shearbox and oedometer test data, and are found to significantly outperform existing empirical correlations based on relative density, highlighting the importance of specifying a suitably detailed site investigation. An improved sliding-block ('Newmark') approach is also developed for estimating permanent deformations during preliminary design, in which the formulation of the yield acceleration is fully strain-dependent, incorporating both material hardening/ softening and geometric hardening (re-grading). The site-specific (improved) FE models and the new sliding-block approach are shown to outperform considerably existing FE parameters and sliding-block models in capturing the permanent deformations of the slope under virgin conditions, and further, only the improved FE and sliding-block models are found to capture correctly the behaviour of the 'damaged' slope under subsequent earthquakes (e.g. strong aftershocks). The FE models can additionally accurately replicate the settlement profile at the crest and quantify the dynamic motions that would be input to supported structures, although these were generally overpredicted. The FE procedures and sliding-block models are therefore complementary, the latter being useful for preliminary design and the former for later detailed design and analysis.

Modelling the seismic performance of rooted slopes from individual root-soil interaction to global slope behaviour T. LIANG Ã , J. A. KNAPPETT Ã and N. DUCKETT † Many natural and man-made slopes are planted with vegetation, and it is known that this can increase the stability of slopes under static conditions. There is anecdotal evidence that vegetated slopes also perform better than fallow slopes during earthquakes. However, the study of the dynamic behaviour of slopes planted with species having dichotomous ('woody') roots is relatively rare owing to the extreme expense and difficulty involved in conducting full-scale dynamic testing on shrubs and trees. In this paper, dynamic centrifuge testing and supporting numerical modelling have been conducted to study this problem. In the centrifuge modelling, ABS plastic rods are used to simulate repeatably the mechanical properties of real roots. The numerical modelling work consisted of two parts. First, a computationally-efficient beam-on-non-linear-Winkler-foundation (BNWF) model using existing p-y formulations from piling engineering was employed to produce a macro-element describing the individual root and soil interaction both pre-and post-failure. By adding contributions from the different root analogues of different diameters, smeared continuum properties were derived that could be included in a fully dynamic, plane-strain continuum, finite-element model in a straightforward way. The BNWF approach was validated against large direct shear tests having stress conditions simulating those in the centrifuge at different potential slip plane depths. The conversion to smeared properties for global time-history analysis of the slope was validated by comparing the continuum finite-element results with the centrifuge test data in terms of both the dynamic response and permanent deformations at the crest, and these demonstrated good agreement. Owing to the simplicity of the BNWF approach and its ability to consider variable root geometries and properties, along with variation of soil properties with depth, it is suggested that the validated approach described will be useful in linking individual root-soil interaction characteristics (root strength and stiffness, diameter variation, root spacing and so on) to global slope behaviour.KEYWORDS: centrifuge modelling; earthquakes; finite-element modelling; numerical modelling; slopes; vegetation INTRODUCTION Vegetation (grasses, shrubs and trees), as an effective and environmentally friendly approach to improving slope stability, improves slope stability mainly through direct mechanical reinforcement of soil and by modifying groundwater conditions by means of evapotranspiration. The net effect of both of these mechanisms is an increase in shear strength within a defined zone around the roots, although only the mechanical effect is present at all times; the hydrological effects potentially disappear following heavy rain. In terms of the direct mechanical effect, many studies have been performed to quantify the increase in soil ...

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Modelling the seismic performance of rooted slopes from individual root-soil interaction to global slope behaviour T. LIANG Ã , J. A. KNAPPETT Ã and N. DUCKETT † Many natural and man-made slopes are planted with vegetation, and it is known that this can increase the stability of slopes under static conditions. There is anecdotal evidence that vegetated slopes also perform better than fallow slopes during earthquakes. However, the study of the dynamic behaviour of slopes planted with species having dichotomous ('woody') roots is relatively rare owing to the extreme expense and difficulty involved in conducting full-scale dynamic testing on shrubs and trees. In this paper, dynamic centrifuge testing and supporting numerical modelling have been conducted to study this problem. In the centrifuge modelling, ABS plastic rods are used to simulate repeatably the mechanical properties of real roots. The numerical modelling work consisted of two parts. First, a computationally-efficient beam-on-non-linear-Winkler-foundation (BNWF) model using existing p-y formulations from piling engineering was employed to produce a macro-element describing the individual root and soil interaction both pre-and post-failure. By adding contributions from the different root analogues of different diameters, smeared continuum properties were derived that could be included in a fully dynamic, plane-strain continuum, finite-element model in a straightforward way. The BNWF approach was validated against large direct shear tests having stress conditions simulating those in the centrifuge at different potential slip plane depths. The conversion to smeared properties for global time-history analysis of the slope was validated by comparing the continuum finite-element results with the centrifuge test data in terms of both the dynamic response and permanent deformations at the crest, and these demonstrated good agreement. Owing to the simplicity of the BNWF approach and its ability to consider variable root geometries and properties, along with variation of soil properties with depth, it is suggested that the validated approach described will be useful in linking individual root-soil interaction characteristics (root strength and stiffness, diameter variation, root spacing and so on) to global slope behaviour.KEYWORDS: centrifuge modelling; earthquakes; finite-element modelling; numerical modelling; slopes; vegetation INTRODUCTION Vegetation (grasses, shrubs and trees), as an effective and environmentally friendly approach to improving slope stability, improves slope stability mainly through direct mechanical reinforcement of soil and by modifying groundwater conditions by means of evapotranspiration. The net effect of both of these mechanisms is an increase in shear strength within a defined zone around the roots, although only the mechanical effect is present at all times; the hydrological effects potentially disappear following heavy rain. In terms of the direct mechanical effect, many studies have been performed to quantify the increase in soil ...

Shake table testing of the dynamic interaction between two and three adjacent buildings (SSSI)Aldaikh, Hesham; Alexander, Nicholas A.; Ibraim, Erdin; Knappett, Jonathan Abstract 9The dynamic interaction of adjacent buildings in cities and urban areas through the soil medium is inevitable. 10This fact has been confirmed by various analytical and numerical studies. However, very little research is 11 available on the physical modelling of the Structure-Soil-Structure Interaction (SSSI) problem and its effect 12 on the dynamics of adjacent structures. In this paper, a series of shaking table tests was conducted at the 13 Earthquake and Large Structures Laboratory (EQUALS) at the University of Bristol to examine the effects of 14 SSSI on the response of a model building when bordered by up to two other model buildings under dynamic 15 excitation. The results indicated that depending on their height, the presence of one or two adjacent building 16 could positively or negatively alter seismic power and peak acceleration responses of a building in 17comparison to when it is tested in isolation. 18 19