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Motivation for this paper stems from experimental investigations that consider how the vertical capacity of a horizontal circular plate anchor in clay changes due to consolidation. These experiments produced interesting time-dependent measurements that prompted a follow-on study, designed to explore the underlying mechanisms. The new experimental data indicate that changes in anchor load during consolidation under a fixed anchor displacement are linked to three distinct mechanisms. The first is a 'stress-relaxation' reduction in anchor load that occurs quasi-instantaneously after the initial anchor movement stops, with a magnitude that is linked to the average strain rate associated with the initial anchor movement. The second is a local consolidation effect that causes a reduction in anchor load over durations that scale with the anchor diameter. The final mechanism occurs simultaneously with the second, but at a slower rate, such that the resulting increase in anchor load becomes apparent at larger values of time. This increase in anchor load is due to dissipation of excess pore pressures developed in the wake of the anchor during the initial anchor movement. These time-dependent changes are considered relevant for the post-installation capacity of offshore anchors and for the capacity of anchors following a large movement event. [ABSTRACT FROM AUTHOR]

Prefabricated and assembled retaining wall systems are gradually becoming the choice for slope stabilisation and earth-retaining structures. However, current prefabricated retaining wall systems are often difficult to apply in complex and variable construction sites due to issues such as inconsistent production dimensions and transportation difficulties. This paper presents a novel prefabricated retaining wall system and reports centrifuge model tests performed to analyse its overall performance. The influence of different infill materials on the performance of the prefabricated retaining wall system was studied. The research findings reveal that the retaining wall system provides significant slope stabilisation effects and can withstand up to four times the stress level of a natural slope. Moreover, the stability of the retaining wall system is more than twice better when infilled with frictional soil compared with that when clay infill is used. Due to its unique structure, it can not only reduce material consumption and carbon dioxide emissions by around 63.94% but also allow planting of green plants in the gaps of components, thereby providing a more sustainable alternative to conventional concrete gravity wall systems. [ABSTRACT FROM AUTHOR]

This study presents an improved in-flight strutting system for centrifuge modelling. Based on the centrifuge model test data, the mobilizable strength design (MSD) method was revised. The modified MSD method extends to the prediction of three-dimensional (3D) deformations in retaining walls due to excavation activities. Initially, an improved in-flight excavation tool used in centrifuge tests was employed to investigate the impacts of staged excavation on the characteristics of wall displacement and ground settlement in two-dimensional (2D) braced excavation. Subsequently, 2D and 3D finite element analyses, calibrated against the centrifuge test data and considering the small strain effect, were conducted to assess the performance of wall displacement, ground settlement, and movement of the underground soil induced by the braced excavation. Moreover, this research proposes a straightforward predictive model based on the modified MSD, specifically for calculating the deformation along the length of retaining walls in 3D braced excavations. The insights and the modified MSD method given in this study may facilitate the design of foundation pit projects, especially when the 3D effects are an essential detail to be considered in these projects. [ABSTRACT FROM AUTHOR]

Displacement-based approaches have been proven to be effective for the seismic design of gravity retaining structures. However, application of these methods to embedded flexible walls, such as anchored steel sheet pile (ASSP) walls, is still an open issue, as the factors affecting the accumulation of permanent displacements of these systems are not fully understood. This paper presents the results of four dynamic centrifuge tests on small-scale models of ASSP walls in uniform dry sand. The experimental results showed that ASSP walls can experience different failure mechanisms depending on their geometry and on the magnitude of accumulated displacements. During the earthquake, the system exhibits an overall increase of its seismic capacity, caused by: (a) progressive mobilisation of the soil passive strength; (b) sand densification; (c) rotation of the walls; and (d) reduction of the retained height. Accounting for these effects in pseudo-static limit equilibrium solutions improved the predictions of both the critical failure mechanism and the maximum internal forces in the structural members. Moreover, it allowed development of an efficient analytical tool for the prediction of the seismic permanent displacements of these systems, based on Newmark's sliding block approach. [ABSTRACT FROM AUTHOR]

Suction bucket jackets are increasingly being used to support bottom-fixed offshore wind turbines. It is generally assumed that contact between the underside of the bucket lid and the seabed is mandatory to safeguard against additional settlement. Lid contact is usually ensured by underwater grout injection, albeit this has a significant impact on the duration and costs of installation. Although grouting is routine, there are limited available data regarding the benefits of ensuring contact between the lid and the soil. This paper presents data from centrifuge tests of completely and partially installed buckets in dense sand subjected to vertical cyclic loading to investigate the role of lid contact. Lid contact was shown to have a discernible effect on displacement accumulation when buckets were loaded beyond the drained skirt capacity in compression. Under these conditions, settlement of a completely installed bucket was limited by lid contact with the soil plug, while partially installed buckets experienced continuous settlement, as expected. The physical evidence indicates complex load transfer mechanisms that are influenced significantly by the drainage conditions. Hence, an understanding of the soil drainage characteristics at a particular site would provide value when evaluating the requirement for under-lid grouting. [ABSTRACT FROM AUTHOR]

The potential for pile tip damage and extrusion buckling has become an increasing concern for the offshore wind industry following the trend toward the use of large-diameter thin-walled pile foundations, either as monopiles or as part of a jacket structure. Extrusion buckling may be triggered by an initial pile tip fabrication imperfection or pile damage during transport and handling. It may also be triggered during driving through strong heterogeneous sediments. Numerical analysis of the problem requires advanced and computationally expensive techniques because of the three-dimensional, dynamic and large-deformation nature of the pile and soil deformations. The problem is addressed here by combining coupled Eulerian–Lagrangian simulations with geotechnical centrifuge model test data in dry dense sand. Both approaches consider pre-dented piles with the objective of estimating the soil strength, characterised by the cone resistance, at which minor initial damage will start to propagate. Simplified analysis of structural dent propagation and radial stresses generated in the soil during advance of a deformed pile led to a simple calculation procedure to assess the potential for extrusion buckling. Reasonably good agreement was achieved between the proposed calculation method, numerical simulations and centrifuge tests data, rendering the approach a valuable screening tool for practical application. [ABSTRACT FROM AUTHOR]

Mat foundations have been widely used as foundations of mobile offshore platforms such as jack-up rigs and installation platforms. Throughout the service period, the mat bears coupled multi-dimensional loads transferred from the superstructure and directly from the environment. Evaluating the bearing capacity of the mat is the premise of offshore platform design. However, there are few studies on the bearing capacity of commonly used irregularly shaped mats under multi-dimensional load conditions. Looking at two types of A-shaped mats on cohesive soil, uniaxial bearing capacities are calculated using the finite element method (FEM) in this study. The centrifuge test was performed to verify the FEM results. Effects of the length-to-width aspect ratio of the foundation on bearing capacities are discussed. The V-H, V-M, and V-H-M failure envelopes of mats with unlimited and zero tension interfaces are obtained. Studies have shown that the uniaxial bearing capacities change monotonously with aspect ratio increases, and that the bearing capacity of a rectangular A-shaped mat is higher than that of a trapezoidal A-shaped mat. The V-H-M envelope with unlimited tension interface condition is ellipsoid-shaped, while that with zero tension interface is scallop-shaped. With the capacity expressions established in the paper, it is possible to quickly check the bearing state of the mat under a given V-H-M load condition, and then assess the safety of the engineering operation. [ABSTRACT FROM AUTHOR]

An experimental campaign is conducted on a 100g centrifuged monopile model, impact driven, into saturated dense sand, down to three embedding depths, corresponding to three slenderness ratios of 5, 4 and 3. These models are instrumented with optical fibres to measure the bending moment profile along the monopile. A new method is developed to determine the experimental soil reaction curves by considering the distributed moment part from the measured bending moment. This distributed moment is assessed by the one-dimensional finite-element (1D FE) model of the PISA (pile soil analysis) method. The key features of this study are: (a) the monopile behaves from pure rotation to combined rotation–flexure as the slenderness ratio is enhanced from 3 to 5, inducing a less pronounced linear rotation–deflection response at ground level; (b) although the distributed moment assessed in the PISA project is very low, the developed method is useful to explore the experimental local behaviour of laterally loaded monopiles; (c) the 1D FE PISA model captures reasonably well the overall behaviour of laterally loaded centrifuged driven monopiles, even if it is less accurate for the local behaviour. [ABSTRACT FROM AUTHOR]

In this research, the potential benefits of using various structural types of cemented soil, including block-type, column-type, and wall-type, to reinforce the active zone behind a quay wall were investigated by experimental and numerical methods. The response of the quay wall and ground was analysed from aspects of soil movement, quay wall displacement, lateral earth pressure, and bending moment, and a close agreement between the experimental and numerical results was observed. Experimental and numerical results showed that the cemented soil effectively prevented potential deep soil sliding, and then lateral displacement of the quay wall and ground deformation was reduced. Among various structural patterns, the case with the block-type cemented soil exhibited smaller lateral earth pressure on the quay wall, while the case with the wall-type cemented soil more effectively reduced the bending moments and lateral displacements of the quay wall; therefore, wall-type cemented soil seems to be more favourable considering their improved performance under the same load intensities and excavation depth. This research provides a hint and guideline for the preliminary design of cemented soil-stabilised sheet pile quay structures in soft clay based on the lateral load-reduction effect of the varying structural types of the cemented soil. [ABSTRACT FROM AUTHOR]

Underground transportation systems often involve multiple tunnels constructed closely together. Previous studies mainly focus on interaction between circular tunnels; by contrast, interaction mechanisms involving non-circular tunnels are not well understood. In this study, four physical three-dimensional centrifuge tests were performed in dry sand, simulating the response of existing circular and horseshoe-shaped tunnels to a newly excavated tunnel. Two different ratios between pillar depth and tunnel diameter (P/D) of 0.5 and 2.0 were considered. Furthermore, three-dimensional numerical back-analyses considering small-strain stiffness were undertaken. Results reveal that the ground settlement above an existing horseshoe-shaped tunnel is less sensitive to pillar depth than for circular ones. Furthermore, for P/D = 0.5, the existing horseshoe-shaped tunnel experiences both vertical and horizontal compression; more stress reduction occurs vertically than horizontally. A circular tunnel for the same pillar depth becomes compressed vertically but elongated horizontally; stress reduction around the existing circular tunnel is less vertically than horizontally. However, for P/D = 2.0, both types of tunnel become elongated vertically and compressed horizontally because of a larger reduction in vertical stresses than horizontal ones. These results demonstrate that both pillar depth and shape profoundly affect tunnel deformation mechanisms. [ABSTRACT FROM AUTHOR]

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]

Long-term heave of basement slabs is a significant problem in cities with overconsolidated clay, such as London. There is a dearth of data to calibrate the methods commonly used by designers to predict heave displacement and swell pressure. This paper presents results from two centrifuge tests aimed at reproducing the phenomenon of long-term basement heave. Reduced scale models of rectangular basements with different slab thicknesses underlain by overconsolidated clay were tested, to investigate the effect of base slab stiffness on heave behaviour. The centrifuge tests provided measurements of the profiles of vertical displacement, bending moments in the slab and contact pressure at the slab–soil interface. This is the first geotechnical centrifuge study to provide simultaneous measurements of vertical displacement and swell pressures during long-term basement heave. Whereas the flexible basement underwent significant differential heave and almost complete relaxation of swell pressures, the stiff basement generated large swell pressures and consequently large bending stresses. These results confirm that the prediction of high heave pressures is a self-fulfilling prophecy: a basement slab with high stiffness will beget large swell pressures. The experimental measurements of swell pressure and heave were compared to predictions by a simplified non-linear method of heave calculation. The simplified non-linear method produced acceptable predictions of total heave. [ABSTRACT FROM AUTHOR]

In this paper, an experimental, numerical and analytical study is conducted on a 2 × 1 bored pile group on saturated sand under combined loading. Initially, a single-degree-of-freedom system founded on the pile group is tested at the ETH Zurich drum centrifuge under vertical, lateral and pushover loading, gaining insights and deriving benchmark results for validation of finite-element (FE) models. The latter account for non-linear soil–pile interaction, using hypoplasticity for sand and appropriate modelling of interfaces and pile response. Combining centrifuge and FE modelling, the governing resistance mechanisms are identified and quantified. The transition from model to prototype scale is achieved after careful consideration of scale effects. The concrete damaged plasticity model is employed to model the non-linear response of the reinforced concrete (RC) piles, accounting for axial load dependency of bending moment capacity. The prototype problem is studied parametrically, deriving failure envelopes for different levels of vertical loading. Distinguishable failure modes are identified, and the contribution of different resistance mechanisms is quantified. Finally, analytical failure envelopes are derived based on limit equilibrium, expanding Broms' theory to pile groups under combined loading. Accounting for the axial load dependency of RC bending moment capacity, the proposed closed-form solutions provide a useful design tool for engineering practice. [ABSTRACT FROM AUTHOR]

Seawalls are constructed by covering and protecting the sloping seashore ground with concrete plates or blocks. Their purpose is to sustain high waves induced by strong winds and prevent ground erosion, but they often collapse, mobilising different modes of failure, including that of the ground. Nevertheless, limited research has been conducted on ground failure caused by high waves. In this study, a series of novel centrifuge model tests was first conducted to investigate the failure mechanisms of seawalls due to wave propagation, focusing on the failure of the ground. Finite-element analyses were subsequently conducted to explore the failures observed in the model tests and to provide further insight as to the state of the ground leading to failure. Two failure modes were demonstrated to prevail: floating of the covering panel and sliding failure of the ground. In addition, of the possible causes of failure, the following three were identified in the current study: increased unit weight and reduced suction from wetting; enhanced seepage force under the panel and around the toe block during backwash; water pressure on the back of the panel and the landward side of the toe block during backwash. [ABSTRACT FROM AUTHOR]

A series of centrifuge tests was conducted to explore the deformation mechanisms and earth pressures mobilised in loose and dense sand for a complete set of passive movement modes of a rigid retaining wall: rotation about the top and base and translation. Sand deformations were measured by particle image velocimetry and earth pressures were observed by a Tekscan pressure mapping system. Simplified linkages between wall displacements, sand strains and earth pressures were built. Superposition of such results would allow designers to predict retaining wall behaviour in sand during the construction sequence as well as ultimate collapse in a mobilisable strength design procedure. [ABSTRACT FROM AUTHOR]

Steel catenary risers (SCRs) provide a cost-effective solution for deepwater oil and gas production. However, SCRs are susceptible to potential fatigue failure due to the cyclic motions of floating platforms. Previous studies on the physical modelling of cyclic SCR–seabed interactions have primarily focused on either the continuous cyclic motion of an SCR or a single rest period between two SCR motion packets. However, our understanding of the development of seabed trenches and excess pore pressure and their effects on SCR fatigue during multiple episodes of SCR motion and soil reconsolidation remains limited. This study presents a newly developed model container capable of modelling three-dimensional SCR motions including heave, surge, sway, and vortex-induced vibration in a geotechnical centrifuge. A centrifuge test is conducted to investigate the vertical cyclic SCR–seabed interaction, considering five vertical cyclic motion packets with intervening periods of reconsolidation. The results indicate that ignoring the effects of reconsolidation leads to an overestimation of the fatigue life of an SCR. In this test, the SCR fatigue life is reduced by 18%–23% after five episodic SCR motion packets and intervening reconsolidation. [ABSTRACT FROM AUTHOR]

Pile foundations are widely used for tall buildings, but determining their capacity and behavior under load often involves expensive and lengthy field tests or imprecise numerical models. This research employed a centrifuge to perform vertical loading tests on single and grouped piles in dry sand, subjected to 100 times gravitational acceleration, to investigate pile capacity and load transfer mechanisms. The results from centrifuge modeling, numerical simulations, and field tests were consistent. The total pile capacity for a single pile was 5800 kN/m², while short and long pile groups had capacities of 6800 kN/m² and 9200 kN/m², respectively. End-bearing accounted for 40% of the capacity in single and short pile groups, and 13% in long pile groups. Surface friction was 95 kN/m² for single piles and 140 kN/m² for grouped piles. A method for estimating total pile capacity based on soil properties showed good agreement with empirical results. [ABSTRACT FROM AUTHOR]

Measuring displacements in model tests typically involves contact-based sensors such as linear potentiometers, where contact between two moving parts occurs at the sensing point. The sensor’s finite mass, the limited stiffness of the beams and the clamping mechanism, and the slippage and hinging of the sensor body could affect the object’s response and lead to measurement errors. Also, the physical mounting rack required to hold these sensors often obstructs the view and makes significant areas unavailable for conducting some other essential investigations. The advancement in high-speed, high-resolution and reasonably priced rugged cameras makes it feasible to obtain better displacement measurements by image analysis. This paper introduces a non-contact method that works by video recording the projection of laser lines on a test object to measure static and dynamic vertical displacements. The technique produces a continuous settlement distribution along the laser line passing through multiple objects of interest. This paper presents the theory for converting laser line images to displacements. The new method’s validity is demonstrated by comparing the results from other measurement techniques: hand measurements, linear potentiometers and three-dimensional stereophotogrammetry.

This study conducted both three-dimensional physical model tests and numerical back-analyses to examine the performance of a single pile subjected to twin tunnelling beneath the pile toe in dry sand. Moreover, numerical parametric analyses were carried out to assess the impact of working load level and tunnel volume loss on pile behaviour. The findings revealed that the first tunnelling induced a 1.9%dp (pile diameter) settlement in the pile when the pile toe was 0.5 D (tunnel diameter) above the twin tunnels, which had a 1.0% volume loss. The settlement was accompanied by an upward load transfer mechanism. The second tunnelling had a reduced impact and induced only 76% of the settlement caused by the first tunnelling. The study also showed that tunnelling-induced shearing behaviours weakened beneath the pile toe with a decrease in working load, resulting in reduced pile head settlement. Moreover, the computed pile settlement increased by 178% when the tunnel volume loss increased from 0.5% to 2%. The findings of this study offer valuable data for the validation and calibration of numerical models. In addition, the outcome from this study provides useful insights into the prediction of the pile-soil-tunnel interaction when subjected to twin tunnelling. [ABSTRACT FROM AUTHOR]

This study investigates the dynamics of granular flows in geotechnical centrifuge models, focusing on the effects of centrifugal and Coriolis accelerations. While conventional laboratory-scale investigations often rely on Froude scaling, geotechnical centrifuge modelling offers a unique advantage in incorporating stress-dependent processes that fundamentally shape flow rheology and dynamics. Using the Discrete Element Method (DEM) and the Lattice-Boltzmann Method (LBM), we simulate the collapse of a just-saturated granular column within a rotating reference frame. The model’s accuracy is validated against expected trends and physical experiments, demonstrating its strong performance in replicating idealised collapse behaviour. Acceleration effects on both macro- and grain-scale dynamics are examined through phase front and coordination number analysis, providing insight on how centrifugal and Coriolis accelerations influence flow structure and mobility. This work enhances our understanding of granular flow dynamics in geotechnical centrifuge models by introducing an interstitial pore fluid and considering multiple factors that influence flow behaviour over a wide parameter space. [ABSTRACT FROM AUTHOR]

The semi-rigid pile-supported composite foundation is widely used in highway projects due to its effectiveness in increasing the bearing capacity and stability of foundations. It is crucial to understand the stress distribution across the embankment width and the behaviour of unreinforced foundations. Thus, five centrifuge tests were conducted to examine the bearing and deformation behaviours of NPRS (Non-Connected Piled Raft Systems) and GRPS (Geosynthetic-Reinforced Pile-Supported systems) with varying substratum stiffness, then a comparative analysis was conducted on embankment settlement, pressures underneath the embankments, and axial forces along the piles. The results indicated that greater substratum stiffness correlates with reduced settlement and deformation at various depths. Deformation occurring 5 meters from the embankment toe includes settlement in NPRS and upward movement in GRPS. The potential sliding surface is primarily located within the embankment in NPRS, whereas it may extend through both the embankment and foundation in GRPS. The pile-soil stress ratio and efficiency in NPRS are higher than in GRPS across the embankment. The axial force borne by end-bearing piles is significantly greater than that by floating piles. As the buried depth increases, the axial force in GRPS initially rises then declines, whereas in NPRS, it remains relatively constant within a certain range before decreasing. This study aids in assessing the applicability of composite foundations in complex railway environments and provides a reference for procedural measures under similar conditions. [ABSTRACT FROM AUTHOR]

The extreme drought–rainfall seesaw is projected to occur with an increasing frequency. However, there still lacks a thorough understanding of its impacts on slope behaviour, in which desiccation crack plays a key role. To address this issue, a centrifuge test was conducted to investigate the effects of drought-induced desiccation crack on slope instability under extreme rainfall. During the test, the non-cracked slope was firstly subjected to extreme rainfall with 100-year return period. Subsequently, a long-term drying was applied to induce desiccation crack, and hence forming a cracked slope. The cracked slope is then subjected to an identical extreme rainfall. The non-cracked slope only exhibits swelling deformation, whereas for the cracked slope, a slip surface (2 m in depth) is clearly observed to initiate from one deep crack at crest. The global sliding failure of the cracked slope is mainly related to preferential flow, which could result in soil shear strength reduction. [ABSTRACT FROM AUTHOR]

Earthquakes generally consist of one mainshock and subsequent aftershocks. Although effects of aftershocks following the mainshock on surface structures has been studied extensively, similar studies on underground structures are rarely reported in the literature. With the fast advances in underground space development, robustness of remediation measures against underground structures uplift induced by soil liquefaction shall be examined to ensure their functioning subject to not only the mainshock but also the subsequent aftershocks. This paper studies the uplift behaviour of a conventional manhole subjected to the mainshock-aftershock sequence. It was found that, in the ground that becomes liquefied during the mainshock, manholes become more vulnerable when faced with aftershocks. Due to this reason, some of the previously proposed remediation measures, such as increasing the manholes’ self-weight, roughening the sidewalls, were examined using centrifuge modeling in this study. It was found that such measures had little effect in the aftershocks despite their effectiveness in the precedent mainshock. In contrast, the methods that mitigates manhole uplift by enhancing the manhole’s base permeability, demonstrated better performance in the aftershock than in the mainshock, indicating its promising application potential in future mitigation design.

The number of incidents worldwide where pile tip damage has occurred during driving has accelerated following the growth of the offshore wind sector, and the expansion into areas with increased risk of embedded boulders or partially weathered soft rocks. The process involving pile–boulder–soil contact can be simulated with advanced three-dimensional (3D) large-deformation dynamic coupled Eulerian–Lagrangian (CEL) finite-element (FE) analysis. However, analyses of this nature are highly time-consuming and computationally expensive. The objective of the paper is to develop a generic framework whereby the potential for denting by a boulder can be assessed a priori. The study encompasses four main components to determine the magnitude of force necessary to create plastic damage of the pile tip and what combination of boulders and soil might generate such reactions during pile installation: (a) a parametric 3D FE structural denting study; (b) a parametric boulder–soil 3D CEL study, where prescribed displacements were applied to the surface of boulders embedded in sand; (c) a range of pile–boulder–soil 3D CEL analyses where a deformable pile and different boulder–soil combinations were simulated; and (d) centrifuge model tests involving tip damage from boulders. Simple relationships and charts have been established from the numerical studies and validated from experimental work. [ABSTRACT FROM AUTHOR]

This work presents a simple two-phase flow model to analyse a series of axisymmetric granular column collapse tests conducted under elevated gravitational accelerations. These columns were prepared with a just-saturated condition, where the granular pores were filled with a Newtonian fluid up to the column’s free surface. In this configuration, unlike the fully submerged case, air-water-grain contact angles may be important to flow dynamics. The interaction between a Newtonian fluid phase and a monodispersed inertial particle phase was captured by an inter-phase interaction term that considers the drag between the two phases as a function of the particle phase porosity. While this experimental setup has broad applications in understanding various industrial processes and natural phenomena, the focus of this study is on its relevance to predicting the motion of debris flows. Debris flows are challenging to model due to their temporally evolving composition, which can lead to the development of complex numerical models that become intractable. The developed numerical scheme in this study reasonably reproduces the particle-size and gravitational acceleration dependencies observed within the experimental runout and basal fluid pressure dissipation data. However, discrepancies between the model and physical experiments primarily arise from the assumption of modelling the granular phase as a continuum, which becomes less appropriate as particle size increases. [ABSTRACT FROM AUTHOR]

Scour leads to the loss of soil around monopile foundations for offshore wind turbines, which affects their structural safety. In this paper, the effect of scour on the lateral behaviour of monopiles was extensively investigated using finite element analysis, and calibration and comparison were undertaken using centrifuge tests. Piles with three slenderness ratios, i.e., 3, 5 and 8, were studied by keeping the diameter constant and varying the embedment length. Three scour types (local narrow, local wide and global) and four scour depths (0.5D, 1D, 1.5D and 2D; D signifies the pile diameter) were considered in this investigation. The results indicate that the lateral resistance of the pile is the greatest in the case of local narrow scour, followed by that in the cases of local wide scour and global scour. When the scour depth is larger than 1D, the influence of the scour type on the pile lateral bearing behaviour is insignificant. The influence of the scour type and scour depth on the pile lateral bearing behaviour is broadly similar for piles with slenderness ratios of 3, 5 and 8. However, the piles featured with smaller embedment lengths show a larger decrease rate in their lateral capacity, which means the effect of scour should cause more concern on small slenderness ratio monopiles. [ABSTRACT FROM AUTHOR]

Extensive studies have been performed on the effectiveness of scour protection against scour erosion progression. But there is little research to date evaluating the effect of scour protection on vertical resistance behaviour of monopile foundations. This paper investigates the influence of scour protection on the vertical loading behaviour of monopiles installed in sand using centrifuge tests and finite element analysis (FEA). Four scour protection widths (1D, 2D, 3D, 4D; where D is the pile diameter) and three scour protection thicknesses (1 m, 2 m, 3 m) were modelled on a pile with a slenderness ratio (L/D) of five. In the FEA, the scour protection mechanism was modelled using two strategies, namely the 'stress method' by applying stress and the 'material method' by applying virtual material on the seabed surface around the pile. Outcomes between these two strategies were compared, and the contact coefficient δ used in the 'material method' for describing the contact effectiveness of the overlaying scour protection material with the pile structure was introduced, providing a more scientific and accurate calculation reference for engineering applications. The results indicated that the vertical capacity of monopiles could be increased by 5% to 23% by adopting the scour protection measure, depending on the scour protection width and scour protection thickness. [ABSTRACT FROM AUTHOR]

A study aimed towards assessing the variation in shaft capacity of piled foundations in swelling clays is presented. At the clay's in-situ water content, the results of pull-out tests on short-length piles revealed no dependency of shaft capacity on overburden stress. Conversely, after achieving a targeted value of swell, a strong dependency on overburden stress was observed. In upper portions of the profile where swell can occur relatively freely, swell-induced softening results in a reduction in pile shaft capacity. However, at greater depths where swell is largely suppressed, so too are the effects of swell-induced softening. For this reason, shaft capacity at depth was found to remain relatively constant before and after swell. The results of an instrumented pile test revealed an overriding dependency of lateral induced swell pressure on the magnitude of heave which has occurred. Irrespective of the level of overburden stress, lateral pressures against the pile were found to increase at early stages of the swelling process, but then reduce as swell continued and softening began to occur. Such a result highlights the importance of carefully considering the level of swell at which shaft capacity should be assessed if a conservative design is to be obtained. [ABSTRACT FROM AUTHOR]

Recently, due to more excavation projects near existing tunnels, the research on tunnel deformation control has become very important and urgent. However, the systematic study of the control effectiveness of partition piles, one of the commonly used methods for controlling tunnel deformation, was not mature yet. In response to this situation, a series of centrifuge modelling studies were performed to explore how nearby existing tunnels respond to excavations with partition piles in a dry sand foundation. The tests provided insights into the variations of the horizontal displacement of retaining walls, surface settlement, the horizontal and vertical displacements of the tunnel, and the circular induced strain of the tunnel. The test results showed that the horizontal displacement of retaining walls exhibited a cantilever-type displacement pattern. The most significant surface settlement occurred near the retaining wall and decreased as the distance from the retaining wall increased. The overall deformation of the tunnel roughly showed an ellipsoidal deformation pattern in the horizontal direction. The maximum horizontal displacement was observed at the right shoulder of the tunnel, while the maximum vertical displacement occurred at the right arch of the tunnel. Increasing the length of the partition piles led to a deterioration in their deformation control effectiveness. The top burial depth of the pile could further improve the control effectiveness of the partition piles. However, when the top burial depth of the pile was excessive and exceeded its critical value, the improvement effect of the burial depth on the partition piles diminished. [ABSTRACT FROM AUTHOR]

Full-scale Accelerated Pavement testing (APT) has been regarded as an essential step to bridge the gap between research and practice for pavement design because it can fully mimic a large number of heavy wheel loading on pavements. Despite being able to test pavements in an accelerated manner compared to Long-term Performance Monitoring (LTPM), conducting one full-scale APT experiment is still demanding in terms of monetary cost, space, time, etc., and the accessibility to APT facilities is only available in a few countries nowadays. In this study, an exploratory APT study with a down-scaled pavement model in a high-g environment created by geotechnical centrifuge was performed with up to half a million simulated aircraft load repetitions. Through this test, it was proved that the centrifuge APT can reproduce the full-scale airfield pavement responses, including rutting, cracking, material fatigue, etc. The transient and permanent deflection of the pavement surface, variations in stress and strain states within the pavement structure over its lifespan can be well captured for analysis. This framework of centrifuge APT provides a new methodology for pavement testing and can significantly save the current cost and time of full-scale APT. [ABSTRACT FROM AUTHOR]

Concrete pavements are typically considered to be rigid pavements and are designed using principles based on the beam-on-elastic support equations as derived by Westergaard in 1926. Ultra-Thin Continuously Reinforced Concrete Pavements (UTCRCP) have been constructed with concrete layers as thin as 40 mm. These pavements have been subjected to millions of load cycles without any noticeable damage. The design of these flexible concrete pavements has proven to be problematic as they are neither rigid nor truly flexible. To investigate the response of UTCRCP to traffic loading, a geotechnical centrifuge was used to test UTCRCP scale models at 10G. The results showed that the centrifugal forces had a significant effect on the stiffness of the scaled model. It was observed that the interaction between the substructure and flexible concrete layer differed notably from the assumed behaviour of both rigid and flexible pavements. When designing UTCRCP, not only the loading pattern caused by the interaction between the wheels on an axle and adjacent axles, but also the rutting of the substructure that results in the concrete layer spanning across gaps below it, causing increased vertical pressure between wheel paths, should be considered. [ABSTRACT FROM AUTHOR]

The touchdown zones of steel catenary risers and lazy wave risers are fatigue hotspots, where the risers interact continuously with the seabed due to hydrodynamic loading exerted on the host vessel. The whole-life interactions can range from small-amplitude daily motion cycles to motions that involve large-amplitude cyclic interaction with the seabed during storm events. A key design challenge that affects the fatigue life of these risers is the accurate modelling of the evolution of the riser–soil stiffness, throughout the whole life of the riser and for different soil conditions, including overconsolidated conditions, which may occur due to the geological history, ageing or biochemical processes of the sediments. This paper describes centrifuge model pipe tests simulating whole-life riser–soil interaction in normally consolidated and uniform overconsolidated clay samples, under successive sequences of cyclic motions. Results confirm that the whole-life soil stiffness evolution depends strongly on cyclic amplitudes, with reconsolidation-induced soil stiffness recovery after heavy remoulding, and is also influenced by the soil overconsolidation ratio, with a reduced tendency for soil hardening at higher soil overconsolidation ratios. This study provides insights into the relevant cyclic soil stiffness to consider when assessing the whole-life design of risers interacting with overconsolidated seabed sediments. [ABSTRACT FROM AUTHOR]

Soft-ground tunnel boring machines (TBMs) are the preferred solution for the construction of long tunnels and linear infrastructure assets, especially in urban areas. TBMs allow the control of tunnel-face stability, minimising the effects on surrounding ground. Unfortunately, existing methods for the assessment of ground surface movements due to TBM tunnelling either utilise complex and computationally expensive numerical analyses or rely on simplistic volume-loss theories, which do not consider the characteristics of the ground and TBM operation. This paper presents a simple formulation to estimate the immediate surface settlement due to the applied TBM support pressure, based on an analogy with the hyperbolic behaviour of stress–strain curves of soils. The variables chosen to describe the ground movement were the maximum surface settlement and volume loss, while the TBM face support pressure is used to describe the tunnel internal support pressure. Uncertainties due to the inherent variability of geotechnical parameters were also considered, resulting in the definition of lower and upper boundaries. Data from a series of centrifuge test results, with and without tunnel-face reinforcement by forepoles, and a real-scale TBM case study were used to validate the proposed model. The analyses show that the proposed model adequately represented the observed settlement data. [ABSTRACT FROM AUTHOR]

This paper presents the results of centrifuge model tests to investigate the deformation behaviour of unreinforced and reinforced transparent soil foundations under strip loading. A digital image analysis technique was employed to obtain the soil displacement field and strain distribution of reinforcements. Two-dimensional (2D) numerical models were developed and verified using the test results. The soil was modelled as a linearly-elastic perfectly-plastic material with Mohr–Coulomb failure criterion. The reinforcement was characterised using a linearly-elastic model considering rupture behaviour. Moreover, a parametric study was conducted to investigate the load–settlement response of foundations, distribution of reinforcement tension and failure sequence of reinforcements. The experimental and numerical studies show that the results obtained from the numerical simulations are in good agreement with the results of the centrifuge model tests. The 2D finite difference model developed using the user-defined functions coded into the FLAC programme can better simulate the progressive failure of the reinforcement layers in the tests. The failure sequence of reinforcement layers is not affected by the modulus and internal friction angle of soil and the reinforcement length, but is closely related to the combined effect of spacing and number of reinforcement layers and the combined effect of reinforcement stiffness and strength. [ABSTRACT FROM AUTHOR]

Two centrifuge model tests were conducted, each with three large diameter steel tubular piles installed under similar conditions, i.e., diameter (Φ) = 2 m; thickness (t) = 25 mm; loading height from the rock surface (HL) = 6.5 m, but different rock socketing depths (dr), i.e., 2 m, 3 m, and 4 m, respectively, in prototype scale. Two additional 1 g model tests were conducted using the same model pile and ground. The results indicate that the pile lateral resistance increased with an increase in the rock socketing depth to diameter ratio (dr/Φ) in both 1 g and 50 g models. However, the difference between the two gravitational acceleration levels became visible in the non-linear behaviour as the imposed displacement increased. Specifically, the 1 g models showed larger residual displacement and less stiffness in reloading than the 50 g models, particularly under cyclic loading. Two types of ultimate failure modes were observed, i.e., rock failure and pile structural failure with local buckling just above the rock surface. The latter failure mode was only attained in the pile with a dr/Φ ratio of 2 in a 50 g models among the test conditions adopted in the models, but not in the 1 g model.

Although deterioration of soil due to freeze–thaw cycles has been investigated based on element tests and small-scale laboratory model tests, there still lacks fundamental understanding of slope response under cyclic freeze–thaw action. In this study, a novel in-flight freeze–thaw system was developed to investigate the thermal, hydraulic and mechanical response of a typical unsaturated slope under seven freeze–thaw cycles in the centrifuge. Temperature, suction and deformation were measured during the test. The test results show that the suction at the freezing front can be up to about 1 MPa. The comparison between measured and theoretically predicted suction elucidates that using the temperature-dependent Clausius–Clapeyron equation is inadequate to model suction evolution precisely when considering water migration. The subsequent thawing reduces the suction to 9 kPa, which is about 60% lower than during the initial unfrozen state. The suction destruction softens the surface soil layer, leading to downslope movement during thawing. During the seasonal downward ratcheting movement, the lower elevation of the slope can flatten from 59° to 50°. The repeated freeze–thaw action generates significant fractures at the soil surface while deep cracks can form due to tensile rupture. Freeze–thaw-induced seasonal variation of suction softens the post-thawed slope, leading to accumulated plastic deformation and shallow slope failure. [ABSTRACT FROM AUTHOR]

This paper presents the results from a systematic investigation into the effects of stress level, penetrometer diameter, penetration depth and relative density on the end resistance (qc) measured in centrifuge-scale cone penetration tests (CPTs) in a variety of normally consolidated siliceous and carbonate sands. Simple empirical formulations are developed that provide a good description of all measurements and that are consistent with expressions developed in calibration chambers and at field scale. The formulations address the significant discrepancies seen between centrifuge and field scale qc profiles and enable development of qc-based correlations for centrifuge tests that are applicable at full scale, as well as providing a means to interpret very shallow CPTs in the field. [ABSTRACT FROM AUTHOR]