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In the event of earthquake-induced liquefaction, structures with shallow foundations can suffer excessive settlement and rotation. In this paper, the rotational response of structures with shallow foundations resting on liquefiable layers with thickness equal to or smaller than the width of the foundation is examined through a series of dynamic centrifuge experiments. Moment–rotation backbone curves are extracted and the corresponding evolution of rocking stiffness with increasing rotation is depicted, in normalised terms. A stiffness attenuation relation is proposed, which can be used for simplified predictions of maximum and residual rotation using rotational spring and dashpot models. Two such examples are presented, one using an iterative, equivalent-linear rotational spring approximation, and one using Masing's rules for cyclic response, extended with Pyke's hypothesis.

This research provides an insight into the previously unexplored aspects of kinematic pile bending, especially for large-intensity earthquakes where the soil behaviour is highly non-linear. In this study, a series of dynamic centrifuge experiments was conducted on pile foundations embedded in a two-layered soil profile to investigate the kinematic effects on pile foundations during model earthquakes. A single pile and a closely spaced 3 × 1 row pile group were used as model pile foundations, and the soil model consisted of a soft clay underlain by dense sand. It was observed that the peak kinematic pile bending moment occurs slightly beneath the interface of the soil layers and this depth is larger for the pile group compared to a single pile. Also, the piles in a group attract lower bending moments but carry larger residual kinematic pile bending moments compared to a single pile. Furthermore, the elastic solutions available in the literature for estimating the kinematic pile bending moments are shown to yield satisfactory results only for small-intensity earthquakes, but vastly underestimate for large-intensity earthquakes, if methods are applied injudiciously. The importance of considering soil non-linearity effects and accurate determination of shear strain at the interface of layered soils during large-intensity earthquakes for a reliable assessment of kinematic pile bending moment from methods in the literature is demonstrated using dynamic centrifuge test data.

Allowing structures to rock during an earthquake can effectively provide base isolation at a relatively small cost. Rocking limits the base shear demand and provides self-centering, but the rocking response depends on energy dissipation caused by interaction with the soil and impacts during re-centering. This paper addresses the computational modeling of buildings that have either been designed to rock on the soil beneath their foundation (foundation rocking) or at the foundation–structure interface (structural rocking). Within OpenSees, foundation and structural rocking were modeled using a beam-on-a-nonlinear-Winkler-foundation model (BNWF) combined with flat-slider elements for footing–soil and superstructure–footing interactions, respectively. The modified with flat-slider elements BNWF model (mBNWF) involves an uplift-dependent stiffness and viscous damping for both vertical and horizontal directions, and a friction–vertical force coupling. The proposed computational model was used to simulate an extensive set of centrifuge tests involving both structural rocking and foundation rocking with sequential excitations. Generally, the proposed modeling approach, without calibration of built-in parameters, adequately captured the response observed in centrifuge experiments. More specifically, the modeling captured the response amplitude and waveform of story accelerations and building rocking angle in most cases, but including potential nonlinear behavior caused by previous ground excitations was in some cases critical to obtain reasonable predictions. This was more profound for foundation rocking due to its inherent dependency on the soil strength and energy dissipation; for structural rocking previous nonlinear response primarily affected the transition time between full contact and rocking, but had a smaller effect on the prediction of maximum response.

A series of dynamic centrifuge experiments was conducted on model pile foundations embedded in a two-layered soil profile consisting of soft-clay layer underlain by dense sand. These experiments were specifically designed to investigate the individual effect of kinematic and inertial loads on a single pile and a 3 × 1 row pile group during model earthquakes. It was observed that the ratio of free-field soil natural frequency to the natural frequency of structure might not govern the phase relationship between the kinematic and inertial loads for pile foundations as reported in some previous research. The phase relationship obtained in this study agrees well with the conventional phase variation between the force and displacement of a viscously damped simple oscillator subjected to a harmonic force. Further, as expected, the pile accelerations and bending moments can be smaller when the kinematic and inertial loads act against each other compared to the case when they act together on the pile foundations. This study also revealed that the peak kinematic pile bending moment will be at the interface of soil layers for both single pile and pile group. However, in the presence of both kinematic and inertial loads, the peak pile bending moment can occur either at the shallower depths or at the interface of soil layers depending on the pile cap rotational constraint.

A series of geotechnical centrifuge tests to investigate the long-term heave behavior of basements in over-consolidated clay was performed, and the profiles of the slab displacement and und...

Zeybek, A.hakim/0000-0001-7096-5770 Induced partial saturation is an innovative soil improvement technique intended to mitigate earthquake-induced liquefaction. Historical records indicate that successive earthquakes may occur in high seismic areas. Therefore, a comprehensive understanding of the response of partially saturated soils to sequential ground motions is of great significance for the rational design and execution of this method in engineering practice. In this study, a series of dynamic centrifuge experiments were conducted to investigate the impacts of sequential ground motions on the behavior of partially saturated soils beneath shallow foundations. Two different shallow foundation models with a bearing pressure of 135 kPa and 50 kPa were examined. Three seismic simulations, in order of increasing amplitudes, were sequentially applied to loosely-packed partially saturated sand models prepared with air injection technique. The assessment of the test results indicated that shallow foundations resting on saturated models of loose sand did suffer excessive settlements with each event, producing a large embedment of the foundation. However, much smaller settlements were recorded for partially saturated ground, and the level of the foundation embedment remained limited in this case. The deformation vector fields also indicated that different displacement mechanisms were observed for each successive event. Ministry of National Education in Turkey The centrifuge experiments were carried out in Cambridge University with the help of the technicians at the Schofield Centre and with the aid of funds offered by the Ministry of National Education in Turkey. Their support is gratefully acknowledged.

Experimental research into the seismic performance of buildings with passive oil dampers has so far been restricted to large-scale testing of frames erected on laboratory shaking tables that ignore the foundation soil below. This simplification of the problem falls short of replicating dynamic soil-structure interaction that would occur in the field. This paper presents the first experimental attempt at utilising high gravity dynamic centrifuge testing to replicate the response of a damped building at a reduced model scale. The paper compares the dynamic response of two similar two-degree-of-freedom model sway frames, one control (bare) frame and one frame equipped with miniature oil dampers, both structures founded on shallow raft foundations in dry dense sand. The miniature oil dampers successfully mitigate floor accelerations, drifts, and storey shear forces in the damped frame with minor modification to the frame stiffness. For strong, near resonance motions, global rocking of the undamped frame associated with physical uplifting of the foundation from the soil surface and subsequent yielding of sand beneath has led to floor acceleration levels, which are comparable to those obtained in the damped building fitted with miniature oil dampers. Assessment of the instrumentation installed on the miniature oil dampers reveals a viscoelastic damper behaviour with a dependency on stroke magnitude and on velocity.

Several techniques have been developed in order to mitigate damage to buildings during and after liquefaction events. Benefits of using vertical drains have been verified by analysing their performance in the soil and evaluating their effectiveness in dissipation of excess pore pressures generated by the earthquake. However, the effect of drains in the soil below structures requires further investigation. In this paper, a dynamic centrifuge test series was carried out to evaluate the performance of a vertical drains arrangement below shallow foundations. High permeable rubble brick was used as coarse material inside the drains to provide positive results not only from a geotechnical point of view but also from an environmental and sustainable perspective. The behaviour of drains was analysed when they are located under shallow foundations of a building, in terms of the excess pore pressures generated during the earthquake and subsequent post-seismic dissipation, the foundation settlement and its dynamic response.

Structural or foundation rocking are effective ways to prevent the development of large force demands in building systems experiencing ground shaking. In practice, structural rocking may result in large displacements and therefore is often accompanied with dampers, while residual and differential settlements are sometimes a barrier for utilisation of foundation rocking. This paper presents a novel approach to test simultaneously in a centrifuge the performances of a building model rocking above its foundation level (structural rocking) and of a dynamically equivalent building rocking below its foundation level (foundation rocking). These tests are used to explore the role of the foundation and soil response when considering the relative trade-offs between the two building types. In the experiments, dry sand was used in both dense and loose states and a series of earthquake excitations were applied. Results demonstrate that the rocking motion of the buildings is evident in the soil response beneath the structures, and foundation rocking causes larger dynamic differential settlements than structural rocking for a given rocking amplitude. However, these differential settlements may still be small enough to be tolerated from a serviceability limit state point of view.

Pile foundations with enlarged bases are effective either in expansive soils or when piles are liable to attract tensile loading. In this paper, the uplift behaviour of enlarged base piles (referred to as under-reamed piles in the text) in layered strata has been experimentally investigated, using half-space small-scale 1g models, and compared with theoretical predictions developed using upper and lower bound theorems. The failure mechanisms observed were characterised using particle image velocimetry (PIV) techniques. It was observed that an upper stratum of clay overlying sand increased the post-peak uplift capacity when compared to two-layered sand, but had little effect at small strain. The small strain failure mechanisms observed were similar, consisting of a balloon-shaped bulb above the pile base, before extending vertically and radially out from the pile with increased displacement. This extension was seen to be wider in the clay than in the sand. These results show that when considering the design of under-reamed pile foundations, anchoring the base of the pile in a stronger stratum at greater depth is beneficial for increasing uplift capacity. At small strains, the overlying stratum has little consequence on the peak uplift resistance. However, at larger strains it can influence the post-peak uplift capacity, which would be an important consideration for possible situations of large imposed displacements.

Structures with shallow foundations resting on liquefiable layers can suffer excessive settlement in the event of an earthquake. The state of practice often estimates the settlement of structures using empirical methodologies. Commonly, these are based on case histories or estimations developed for the free-field. Their reliability has been contested due to uncertainties regarding the dominant deformation mechanisms in the presence of a structure. Here, six dynamic centrifuge tests are presented, investigating the response of structures with shallow foundations resting on liquefiable layers of different thickness. Particle Image Velocimetry (GeoPIV) was used to capture the developed deformation mechanisms. A structure resting on a deep liquefiable layer was found to settle primarily due to increased lateral soil displacements taking place beneath a bulb of stiffer soil formed below the foundation. In shallower layers, this bulb reached the base of the layer, transmitting large accelerations to the structure and promoting a rocking response. Settlement in this case was generated due to increased soil displacement from under the edges of the foundation. In no case were methodologies aimed for the free-field able to account for the salient settlement-generation mechanisms.

The growing energy needs of urban areas and the current environmental context have led to the development of new energy technologies. Since the 1980s, energy geo-structures have been developed and applied, in which heat exchanger pipes are attached to the reinforcement cages of geotechnical structures such as pile foundations or diaphragm walls. By circulating a heat transfer fluid in these pipes, and using a heat pump, these low-enthalpy solutions make it possible to produce heating and cooling with significantly reduced CO2 emissions. However, the cyclic thermal loading generates stresses and strains in the geo-structure and in the surrounding soil, due to thermal expansion. Research on the behaviour of energy pile groups is rather limited, particularly for piled foundations in which only a few piles within a group are thermally activated. Indeed, the implementation of this type of energy technology is slow because of the many concerns about the impact of thermal cycles on the mechanical behaviour of the piles. The complexity of this problem is increased if a natural groundwater flow is present, as this has the potential to affect significantly heat transfer between piles in the group.To tackle these questions, the stresses induced in pile groups by thermal activation were studied by geotechnical centrifuge modelling. Two reduced scale models of 2*2 pile groups were examined, one in dry and one in saturated Hostun sand. In the tests, only one pile was subjected to cyclic thermal loading, but all the pile heads were connected to the same raft. The model piles were cast in cement and copper pipes were used to model simultaneously the reinforcement cages and the heat exchanger pipes. This modelling highlighted that, when heated, the energy pile goes into additional compression along with the diagonally opposite pile, due to the raft rotation. The other two thermally inactive piles showed a decrease of axial load. The saturation of the sand layer displayed a strong role not only on the transient response, but also on the thermal equilibrium due to additional thermal inertia.In order to make relevant comparisons between the observations made on the reduced scale models and those made at prototype scale, scaling laws must be respected, so that the model and the full-scale structure undergo the same physical phenomena. Therefore, preliminary theoretical work was carried out to examine the various thermal phenomena involved. For each phenomenon of interest, the quantities that allow keeping dimensionless numbers identical or at least of the same order of magnitude are studied. Some phenomena were verified also numerically or experimentally. This work is presented in the form of a catalog of scaling laws derived for both mechanical and thermal behaviour of pile foundations.

This research investigates the influence of pile spacing on the dynamic behavior of pile groups by performing a series of specifically designed dynamic centrifuge experiments on pile founda...

Monopiles and gravity base foundations (GBF) are two of the most commonly used foundations for offshore wind turbines. As resonance can cause damage and even failure of wind turbines, understanding the difference between the dynamic responses of monopiles and GBFs under free vibration is important. However there is little experimental data regarding their natural frequency, especially from model tests carried out at correct stress levels. This paper presents the results of novel monopile and GBF tests using a centrifuge to directly determine the natural frequency (fn) of the foundation-soil system. The natural frequencies of wind turbine monopiles and GBFs in centrifuge models were measured during harmonic loading using a piezo-actuator, with the results confirming that soil-structure interaction must be considered to obtain the system’s natural frequency as this frequency reduces substantially from fixed-base values. These results will contribute in preventing resonance induced damage in wind-turbines.

Earthquake-induced liquefaction causes extensive damage to infrastructure. Soil liquefaction-induced effects can account for a significant proportion of damage such as the settlement of existing buildings on liquefiable soils. The influence of structures on the behavior of liquefiable soil is complex. In this paper, the effect of bearing pressure on liquefaction-induced settlement in layered soils was studied. Two 1 g shaking table tests, with different model buildings and bearing pressures, were conducted to establish the ultimate settlement of different structures in liquefiable layered soils. The results showed that as expected the settlement of the heavier building was larger than that of the lighter one. However, the settlement ratio of two buildings was smaller than the bearing pressure ratio. This study will be used as a benchmark for further testing on improving performance through the use of soil reinforcement methods.

It is not uncommon for buildings requiring good seismic performance, with objectives of immediate occupancy and continuous operation, to be equipped with supplemental damping devices. Oil dampers are a popular type of velocity-dependant devices that can be fitted into a structure without incurring considerable changes to the frame stiffness. Seminal experimental work into the seismic performance of structures with viscous dampers is based primarily on large-scale testing of prototype frames fixed to rigid shaking tables overlooking ground flexibility effects. Most literature examining the effects of soil-structure interaction (SSI) on the behaviour of structures with viscous dampers use highly idealised representations of the foundation-soil system stiffness and damping characteristics. This paper utilises high gravity dynamic centrifuge testing to investigate the effects of different base fixity conditions on the seismic behaviour of two model shear structures; one fitted with miniature oil dampers and one left bare for comparison. The base fixity conditions replicated are full base fixity and shallow embedment into dry, dense and loose sand. Experimental results indicate that the damped frame is less responsive to changes in ground compliance relative to its bare frame counterpart. Any apparent drop in damper control with reduced base fixity is driven by improvements in the seismic performance of the bare frame benchmark rather than an increase in the dynamic response of the damped structure. Despite the adverse effects of reduced base fixity on the energy dissipated by the dampers, SSI did not negatively affect the performance of the damped frame.

Countermeasure techniques against earthquake-induced liquefaction aim to mitigate damage on infrastructures. Vertical drains performance has been evaluated during the last decades showing effectiveness in the reduction of structural damage. The performance of alternative drain arrangements considering the influence of existing buildings have been recently analyzed showing positive results on foundations settlement reduction. Although geotechnical mitigation measures main objective is to reduce detrimental effects in buildings, it is also important to incorporate economic and environmentally sustainable solutions. In this paper, the use of recycled coarse material inside drains such as high permeable rubble brick obtained from post-earthquake debris or buildings demolition is examined. Dynamic centrifuge test series was carried out to evaluate the performance of rubble brick vertical drains placed around existing foundations with different loads. The study shows the influence of the foundation load variation on the excess pore pressure generation due to earthquakes, the following post-seismic dissipation, and the foundation response.

Funder: Gates Cambridge Trust (GB), One of the most prevalent causes of bridge failure around the world is “scour”—the gradual erosion of soil around a bridge foundation due to fast-flowing water. A reliable technique for monitoring scour would help bridge engineers take timely countermeasures to safeguard against failure. Although vibration-based techniques for monitoring structural damage have had limited success, primarily due to insufficient sensitivity, these have tended to focus on the detection of local damage. High natural frequency sensitivity has recently been reported for scour damage. Previous experiments to investigate this have been limited as a result of the cost of full-scale testing and the fact that scaled-down soil-structure models tested outside a centrifuge do not adequately simulate full-scale behaviour. This paper describes the development of what is believed to be the first-ever centrifuge-testing programme to establish the sensitivity of bridge natural frequency to scour. A 1/60 scale model of a two-span integral bridge with 15 m spans was tested at varying levels of scour. For the fundamental mode of vibration, these tests found up to a 40% variation in natural frequency for 30% loss of embedment. Models of three other types of foundation, which represent a shallow pad foundation, a deep pile bent and a deep monopile, were also tested in the centrifuge at different scour levels. The shallow foundation model showed lower frequency sensitivity to scour than the deep foundation models. Another important finding is that the frequency sensitivity to “global scour” is slightly higher than the sensitivity to “local scour”, for all foundation types. The level of frequency sensitivity (3.1–44% per scour depth equivalent to 30% of embedment of scour) detected in this experiment demonstrates the potential for using natural frequency as an indicator of both local and global scour of bridges, particularly those with deep foundations.

Gravity wharf (GW) structures are gaining popularity in new port constructions, as well as expanding existing ports. When such structures are located on saturated alluvial seabed, their se...

The paper presents a state-of-the-art review of the current understanding of the seismic behaviour of tunnels. Emphasis is placed on recorded responses of actual tunnels during past earthquakes, as well as relevant experimental studies. In particular, the observed seismic performance of tunnels is initially discussed, by providing cases of reported damage during past earthquakes. This is followed by a review of the current monitoring systems for this infrastructure, which can be used to create future case studies based on actual recordings of the seismic response. Subsequently, the paper provides a summary of relevant experimental studies that took place in the centrifuge or on shaking tables, followed by a short discussion of current analytical models, simplified methods and numerical schemes for the seismic analysis and vulnerability assessment of tunnels. Throughout the presentation, the current overall gaps in understanding the seismic response of tunnels are identified in an attempt to stimulate further work in these areas by the research community., Tunnelling and Underground Space Technology, 99, ISSN:0886-7798, ISSN:1878-4364

In recent years, much of the research in geotechnical earthquake engineering has focused on liquefaction of loose, saturated sands and silts. However, the dynamic behaviour of soft, clayey soils and their interaction with pile foundations during the earthquakes have received relatively little attention. In this study, an attempt is made to investigate the dynamic behaviour of soft clay and its interaction with pile foundations during earthquakes using high gravity centrifuge testing. A model single pile and two sets of 3 × 1 row model pile groups with different pile spacing were embedded in soft kaolin clay and tested under the action of model earthquakes at 50 times the earth’s gravity. The strength and stiffness of clay were evaluated using a T-bar test and an air hammer device respectively. The focus of this research is to investigate the dynamic response of friction piles in soft clay. However, this depends on the dynamic response of the soft clay layer around the pile. To this end, one-dimensional ground response analysis was performed using DEEPSOIL software to emphasise the importance of non-linear analysis in characterising the seismic behaviour of soft clays. It will be shown that clay response depends both on the earthquake intensity and the shear strength and stiffness of the clay layer. This has a direct bearing on the response of single piles and pile groups, with larger amplification occurring for small intensity earthquakes and attenuation occurring for stronger earthquakes.

The Liquefaction Experiments and Analysis Projects (LEAP) is an international effort to produce a set of high quality test data and to then use it in a validation exercise of existing computational models and simulation procedures for soil liquefaction analysis. A validation effort (LEAP-GWU 2015) was undertaken using a benchmark centrifuge model of a sloping deposit tested in a rigid-wall container. This article presents and discusses the shear stress-strain responses and effective stress paths of the LEAP-GW 2015 centrifuge tests and numerical predictions (including an assessment of the effects of the rigid boundaries).

LEAP (Liquefaction Experiments and Analysis Projects) is an effort to formalize the process and provide data needed for validation of numerical models designed to predict liquefaction phenomena. For LEAP-GWU-2015, one project within LEAP, an experiment was repeated at 6 centrifuge facilities (Cambridge University, Kyoto University, University of California Davis, National Central University, Rensselaer Polytechnic Institute, and Zhejiang University) and the results were shared and archived for the purposes of validation of numerical models. This paper describes the specifications for the LEAP-GWU-2015 experiment and compares the experimental results from the six facilities. The specified experiment was for uniform medium dense sand with a 5 degree slope in a rigid container subject to a ramped, 1 Hz sine wave base motion. The experiment was meant to be relatively simple to enable different facilities to produce comparable experiments. Although it cannot be claimed that identical experiments were precisely replicated on different centrifuges, it is argued that the results are similar enough that each experiment lends veracity to the set of results. A benefit of variability between experiments is that the variety enables a more general validation. Important lessons with regard to specification of future experiments for validation of numerical models are summarized. LEAP-GWU-2015 has demonstrated an approach that is a useful reference for future validation studies.

As part of the LEAP-GWU-2015 exercise, a dynamic centrifuge test was conducted at the University of Cambridge on a 5° slope of medium dense Ottawa F-65 sand. The model preparation and saturation details are presented in this paper. This paper presents the experimental data recorded during small and large magnitude sinusoidal ground motions. After the experiment, numerical simulations of the experiment were performed using the finite element code Swandyne. The results from these numerical analyses are compared with the centrifuge test data and the deformations observed during the post-test investigations. The numerical analyses replicated many of the salient features of the test, such as the overall generation of excess pore pressures and attenuation of accelerations in the liquefying ground. More subtle results, such as the de-liquefaction shocks and the asymmetric response due to differences in upslope and downslope accelerations were less well captured in terms of the expected spikes in the dynamic excess pore pressures and accelerations. Overall, the combination of centrifuge testing and numerical analysis were found to complement each other well.

The first author wishes to acknowledge the financial assistance provided during the course of this study by the Ministry of National Education (M.E.B.) of Turkey.

Recently, artificially introducing gas/air into liquefiable soils has been presented as a method for reducing the risks from liquefaction. Although this method offers a simple and cheap solution, its use in practical applications is still very limited. This might be primarily ascribed to the concerns of practising engineers about the durability of gas/air bubbles in soils over time. This paper discusses the durability of entrapped air bubbles under various simulated field conditions that may potentially cause the dissolution, diffusion, compression and escape of air bubbles. Multiple series of 1g vertical sand column and high-g centrifuge tests were undertaken to provide insights into the problem. Air-induced partially saturated soils were prepared using an air-injection technique. The test results showed that the majority of entrapped air bubbles in soils can persist under several simulated field conditions for a sufficient period of time, indicating the long-term reliability of the mitigation accomplished.

Reducing the risk of structural damage due to earthquake-induced liquefaction in new and existing buildings is a challenging problem in geotechnical engineering. Drainage countermeasure techniques against liquefaction have been studied over the last decades with an emphasis on the use of vertical drains. This technique aims to allow a rapid dissipation of excess pore pressures generated in the soil during the earthquake thereby limiting the peak excess pore pressures and consequently improve the structural response. Rapid drainage in the post-earthquake period in the presence of these drains helps quick recovery of the soil strength. Recent studies propose different variations in the vertical drains arrangement to improve the excess pore pressure redistribution in the soil around structures. However, conventional arrangements for existing buildings do not achieve an adequate proximity from the drains to the soil below the foundation. To address this, the performance of inclined and vertical perimeter drain arrangements are studied in this paper. Dynamic centrifuge tests were carried out for the different arrangements in order to evaluate the excess pore pressure generation due to ground shaking and the following dissipation together with the foundation settlement and dynamic response.

This paper describes the specifications developed by and distributed to all of the centrifuge test facilities involved in LEAP-UCD-2017. The specified experiment consisted of a submerged medium dense clean sand with a 5-degree slope subjected to 1 Hz ramped sine wave base motion in a rigid container. This document describes the detailed geometry, sensor locations, methods of preparation, quality control, shaking motions, surface markers, and surface survey techniques.

This paper compares experimental results from every facility for LEAP-UCD-2017. The specified experiment consisted of a submerged medium-dense clean sand with a 5-degree slope subjected to 1 Hz ramped sine wave base motion in a rigid container. The ground motions and soil density were intentionally varied from experiment to experiment in hopes of defining the slope of the relational trend between response (e.g., displacement, pore pressure), intensity of shaking, and density or relative density. This paper is also intended to serve as a useful starting point for overview of the experimental results and to help others find specific experiments if they want to select a subset for further analysis. The results of the experiments show significant differences between each other, but the responses show a significant correlation, R2 ~ 0.7–0.8, to the known variation of the input parameters.

The experimental results of LEAP (Liquefaction Experiments and Analysis Projects) centrifuge test replicas of a saturated sloping deposit are used to assess the sensitivity of soil accelerations to variability in input motion and soil deposition. A difference metric is used to quantify the dissimilarities between recorded acceleration time histories. This metric is uniquely decomposed in terms of four difference component measures associated with phase, frequency shift, amplitude at 1 Hz, and amplitude of frequency components higher than 2 Hz (2 + Hz). The sensitivity of the deposit response accelerations to differences in input motion amplitude at 1 Hz and 2 + Hz and cone penetration resistance (used as a measure reflecting soil deposition and initial grain packing condition) was obtained using a Gaussian process-based kriging. These accelerations were found to be more sensitive to variations in cone penetration resistance values than to the amplitude of the input motion 1 Hz and 2 + Hz (frequency) components. The sensitivity functions associated with this resistance parameter were found to be substantially nonlinear.

Partially saturated soils associated with the presence of occluded air bubbles are commonly encountered in seismically active zones. Yet, there is a lack of deep understanding of the mechanisms of settlement that partially saturated soils suffer during seismic events. Consequently, a reliable seismic design approach for use in engineering practice is lacking. The aim of this paper is to show that seismically induced settlement of a level deposit of partially saturated soil can be estimated by summing the settlement related to excess pore pressure (EPP) generation/dissipation and increased soil mass compressibility in the presence of air bubbles, which are calculated separately. Predictions of the proposed effective stress-based methodology are found to be in good agreement with geotechnical centrifuge measurements. It is shown that the variation of degree of saturation is of significance. The proposed methodology utilizes the degree of saturation as a parameter and can satisfactorily predict the experimentally observed settlement. © 2019 American Society of Civil Engineers.

Gravity Wharf Structures are widely used worldwide to form shallow and deep water ports. They are large structures with a height of 25–50 m depending on the water depth. When these structures are to be sited on loose to medium dense sand, earthquake induced liquefaction settlements present a significant risk. This often requires expensive soil replacement or other ground improvement techniques. In this paper, the dynamic behaviour of these large structures that exert very high bearing pressures on the foundation soil was investigated for the first time. The level of settlements they can suffer due to soil liquefaction was investigated using dynamic centrifuge testing. It will be shown that the full liquefaction does not occur below the structure even when the free field soil fully liquefies during strong earthquakes. However there will be some stiffness degradation owing to excess pore pressure generation and consequent structural settlements. The level of these settlements are considered to be acceptable from a Service Limit State (SLS) perspective. In addition to this the hydro-dynamic pressures that act on the Gravity Wharf structure were also investigated.

This article presents a model preparation methodology for simulating the seismic behavior of a gentle slope in clay with the presence of a soft, weak layer employing centrifuge testing. The model consisted of a three-layered slope of relatively soft clay with a 3° inclination, representative of Brazilian marine subsoils. In-flight characterization of the undrained shear strength and shear wave velocity profiles were achieved through T-bar penetrometer and air hammer tests. The model was subjected to a series of earthquake simulations at different amplitudes, and the response was tracked with accelerometers and displacement transducers. Additional data were obtained using a particle image velocimetry (PIV) methodology also described in this work. The results show that the proposed model preparation methodology enables the simulation of the strength contrast between the weak and relatively stronger surrounding layers using a laminar container. The additional displacement and acceleration data obtained from the PIV were in good agreement with the corresponding displacement transducer and accelerometer measurements. From the spectral analysis, a shift in the fundamental period was observed as the strain amplitude was increased, suggesting that strain rate effects mobilize higher stresses and a strength rate correction should be considered for the calibration of numerical models and comparison with existing methods for calculation of dynamic displacements in slopes.

The European offshore wind sector has been undergoing tremendous growth, resulting in offshore wind farms having larger wind turbines that are located further away from the shore in harsh environmental conditions. To cater for the resulting higher loads, the current trend has been to continually increase the size of the monopile, which is the most popular foundation type. However, this is not viable in the long term given the current installation technology. This paper presents the results of three-dimensional finite-element analyses investigating the improvement in the lateral capacity of a large-diameter monopile in clay when used in combination with hybrid features and rock armour. Non-skirted reinforced concrete and steel footings, a skirted steel footing and steel fins were assessed under a combination of vertical, lateral and moment loads expected at an offshore wind farm location with a water depth of 30 m. The findings, based on shear and bending moment developed in the monopile and mobilised soil resistance, indicate the skirted steel footing and fins to be the most effective in enhancing monopile lateral capacity at serviceability.

This paper outlines the results of an experimental program carried out on centrifuge models of cantilevered and propped retaining walls embedded in saturated sand. The main aim of the paper is to investigate the dynamic response of these structures when the foundation soil is saturated by measuring the accelerations and pore pressures in the soil, displacements and bending moment of the walls. A comparison among tests with different geometrical configurations and relative density of the soil is presented. The centrifuge models were subjected to dynamic loading in the form of sinusoidal accelerations applied at the base of the models. This paper also presents data from pressure sensors used to measure total earth pressure on the walls. Furthermore, these results are compared with previous dynamic centrifuge tests on flexible retaining walls in dry sand.

Earthquake-induced liquefaction of soils can result in floatation failure of lightweight buried structures such as tunnels, with the potential for economic and human loss. Ground improvement around a tunnel is one approach to preventing this mode of failure. Four 1-g shaking table tests have been conducted including a reference test with a tunnel in unimproved liquefiable ground, and three tests with different geometries of coarse-grained granular backfill replacing areas of the liquefiable layer around the tunnel. It was observed that ground improvement performed below the tunnel was most effective at reducing uplift during earthquake loading. This was attributed to the reduction of excess pore water pressure (EPP) acting on the tunnel invert and the restriction of the flow of liquefied soil around the tunnel needed to facilitate the uplift. In contrast, ground improvement above the tunnel showed very little benefit in reducing uplift compared to the reference test. The ground improvement above the tunnel was unable to retain sufficient shear strength to restrain the buoyancy of the tunnel and, once uplift had been initiated, was unable to restrict the flow of liquefied soil that would have restricted the uplift to a small value. This suggests that, for shallow tunnels, restricting the flow of the liquefied soil and alleviating EPP acting on the invert is more important than preserving shear strength above the tunnel when designing remediation schemes against uplift.

Seismically induced accelerations are greatly affected by the transmission through soil layers. The stiffness and damping of the material beneath a structure can therefore influence the seismic loads experienced in the structure. Recently, there has been interest in the use of very low shear stiffness materials in subsoil beneath structures in order to act as a filter to seismic motions, but there is significant skepticism as to its practicability. In this chapter, some notable contributions are discussed, and some work showing the physical modelling and numerical modelling of a soft-material scheme that showed initial promise is presented. This is seen to be readily modelled as a simple mass-spring system, which could be applied to other similar cases. Future challenges include development of a suitable material for the purpose, and reliably proving static stability.

© 2018 The Authors Earthquake Engineering & Structural Dynamics Published by John Wiley & Sons Ltd Rocking motion, established in either the superstructure in the form of a 2-point stepping mechanism (structural rocking) or resulting from rotational motion of the foundation on the soil (foundation rocking), is considered an effective, low-cost base isolation technique. This paper unifies for the first time the 2 types of rocking motion under a common experimental campaign, so that on the one hand, structural rocking can be examined under the influence of soil and on the other, foundation rocking can be examined under the influence of a linear elastic superstructure. Two building models, designed to rock above or below their foundation level so that they can reproduce structural and foundation rocking respectively, were tested side by side in a centrifuge. The models were placed on a dry sandbed and subjected to a sequence of earthquake motions. The range of rocking amplitude that is required for base isolation was quantified. Overall, it is shown that the relative density of sand does not influence structural rocking, while for foundation rocking, the change from dense to loose sand can affect the time-frequency response significantly and lead to a more predictable behaviour.