Shared pile anchoring enables multiple floating wind turbines to be secured to a single foundation, offering significant potential to reduce mooring costs and environmental impact. However, this concept introduces complex multi-directional cyclic loading on anchor piles, which remains insufficiently understood and is not yet addressed in current design guidelines. Preliminary evidence suggests that such loading may adversely affect pile response. This paper presents a combined experimental and numerical study to improve the understanding of soil–pile interaction under multi-directional loading. A sun-type lateral loading pattern, consisting of monotonic load sequences applied at 30° increments, is analysed. This study (i) characterises the pile response under this loading scheme, (ii) validates a numerical model for further investigation of multi-directional cyclic loading, (iii) examines the evolution of the p–y curves, and (iv) demonstrates how combined physical and numerical modelling can highlight the three-dimensional effects on soil response, including void ratio changes. Overall, the work presents a combined approach to better understand soil behaviour around the pile shaft under complex loading paths, providing a basis for the development of more robust and reliable design methods for floating wind turbine shared anchors.
This study investigates the dynamic response and load-sharing mechanism of a piled raft foundation subjected to earthquake loading. A series of 1g shaking table tests was conducted to analyse the dynamic behaviour of soil–structure interaction. The experimental setup involved models of two- and five-story aluminium frame structures supported by a 3 × 3 piled raft foundation embedded in fully saturated Jumunjin sand under both loose and dense conditions. The results reveal that effective stress recovery occurs at varying depths and progresses more rapidly in the lower layers, while the shallower strata experienced excess pore water pressure ratios approaching 1. In loose sand, where piles remain stiff, but the surrounding soil is soft, peak ground acceleration response reached approximately 200% of the input acceleration at intermediate depths, decreasing down to 130% towards the surface. Notably, under dynamic excitation, the load supported by friction piles decreased by 30% and was gradually transferred to the raft as shaft resistance decreased. In contrast, in end-bearing pile conditions, soil compaction and loss of contact with the raft helped maintain pile resistance, allowing the piles to carry approximately 90%–100% of the applied load. These findings highlight the importance of considering soil density and pile bearing type in the seismic design of piled raft foundations, particularly in regions with deep bedrock.
This study presents the first rigorous experimental validation of seismic resonant metamaterials for structural protection against vertically propagating horizontal seismic shear waves. Its primary goal is to assess the effectiveness of metabarriers (arrays of soil-embedded, unit-cell resonant metamaterials) in attenuating structural vibrations induced by real earthquake ground motions. Two dynamic centrifuge model tests were conducted at 50 g at the Zurich Geotechnical Centrifuge Centre. The first experiment simulates the seismic response of an unprotected single-degree-of-freedom structure. In the second, unit-cell resonant metamaterials are embedded in the soil on both sides of the structure. Both models are subjected to identical seismic excitations, enabling direct comparison. The 3D-printed unit cells are equipped with tuned internal masses to achieve a horizontal vibration frequency of 150 Hz, close to the structure's fixed-base frequency of 160 Hz. A laminar container is used to ensure realistic boundary conditions, filled with dense Hostun sand. Instrumentation includes accelerometers in the soil, on the container, and on the structure, as well as high-speed cameras for digital image correlation (). Frequency-domain analysis shows that resonant metamaterials significantly reduce structural and near-field accelerations at resonance, with revealing the underlying protective mechanism, caused by the out-of-phase vibration of the unit-cell masses relative to the soil.
Debris flows and rapid gravity-driven mass movements, including mud flows, pose major geotechnical hazards in natural and engineered settings. Physical modelling in geotechnical centrifuges offers a controlled framework for investigating these phenomena, provided that appropriate scaling laws are satisfied. This paper presents drum-centrifuge experiments on mud flows, focusing on the assessment of inertial scaling through the modelling of model approach. The theoretical framework is based on a reduced, depth-integrated form of the Navier-Stokes equations for shallow, non-turbulent, non-Newtonian flows. Velocity-displacement relationships obtained at different centrifugal acceleration levels are compared at prototype scale. The results identify a quasi-linear propagation regime associated with an inertial-gravitational balance, in which velocity-displacement trends become approximately linear and converge after prototype-scale normalisation. This convergence provides experimental support for inertial similitude within the identified regime. Outside this interval, deviations arise as temporal acceleration and dissipative mechanisms become more relevant. The findings emphasise that inertial scaling in centrifuge modelling is regime-specific. They also show that, although local kinematic quantities satisfy inertial scaling during propagation, global outcomes such as runout distance are affected by processes outside the similitude regime and should be interpreted with caution.
Permanent fault dislocation is a significant geological phenomenon that can cause severe damage to earth dams and must be considered in seismic design. In this study, to address existing uncertainties and close current knowledge gaps, a series of centrifuge experiments at an acceleration of n = 60 g, followed by finite element analyses, were performed to evaluate the fault rupture path in earth dams with clayey cores constructed on alluvial foundation layers. During faulting, the deformation pattern and the pure vertical movements at various locations were monitored. The results indicate that earth dams subjected to normal faulting may experience substantial damage, ranging from considerable deformation in the shell to transverse cracking in the core. Moreover, reducing the thickness of the alluvial foundation layer intensifies the induced damage. The presence of a cutoff wall at the centre of the core further amplified the damage observed in this study’s configurations. Although centrifuge modelling involves limitations such as height constraints and the absence of reservoir water, the experiments provide valuable insights about dam’s behaviour during fault rupture.
The transmission of seismic tectonic plate movements to near-surface soils can cause large, rapid, and damaging faults. These deformations can cause catastrophic failure of foundations and buildings at the surface, as well as buried utilities that are near or spanning a fault. Correctly predicting the fault propagation to assess risk to existing structures or for safe zoning is crucial yet challenging due to soil non-linearity, large soil deformations, and dynamic effects. Geotechnical centrifuge modelling enables this complex and large-scale phenomenon to be captured with reduced-scale models. The current study presents the development of a compact fault rupture simulator compatible with the medium-sized 15 g-ton centrifuge at Boulder. The setup allows comparison of the rupture propagation in soils subjected to quasi-static and dynamic normal fault rupture. The contrasting uses of multiple instrumentation techniques are highlighted, for example, tracking the soil displacements directly versus inferred from accelerometers detecting the radial g-field in the quasi-static tests versus obtaining static and dynamic acceleration changes during the dynamic faulting. Overall, differences in the observed rupture propagation due to the vertical accelerations are demonstrated in two identically prepared dry sand models, highlighting an often-ignored rate effect in this complex process.
This study investigates the effectiveness of a slope reinforcement system consisting of a network of recycled plastic posts interconnected at the slope surface with a geogrid. Centrifuge and numerical modelling were performed to study the shear resistance of soils reinforced by posts with or without geogrid connection. A large-area, direct shear apparatus that can be mounted on a centrifuge was utilised so that a soil block could be sheared at a predefined slip depth under a prototype-scale effective stress state. Eleven tests were conducted to study the effects of soil density, post spacing, and geogrid connection on the shear behaviour of the reinforced soil. The soil–structure interaction was analysed by the beam-on-non-linear-Winkler-foundation approach. The reinforcement effect was maximum when slip occurred at the mid-length of the post. For a deep slip, the reinforced soil followed an “intermediate mode” of failure, where the soil strength was fully mobilised along the post length. The geogrid increased the shear resistance of the reinforced soil, but these benefits were at the cost of additional mobilisation of bending stresses within the connected posts. Despite the significant improvements of soil stability, careful monitoring of the reinforced system might be required to prevent post overstress and yielding.
This paper presents the results of large-scale uplift tests on pad foundations conducted at the Soil-Foundation-Structure Interaction Laboratory at the University of Bristol, simulating conditions relevant to overhead electrical line infrastructure. Pad foundations with a 1 m & times; 1 m footprint and different geometries were embedded at depths of up to 2 m in manually compacted dry sand. The results complement and validate previous centrifuge tests, and numerical modelling studies aimed at improving current foundation design practices. They confirm: (i) the superiority of theoretical uplift-prediction methods that account for both the weight of the soil wedge and the frictional forces mobilised along the failure planes, both governed by soil dilation; (ii) the potential for optimising foundation geometry through chamfering to increase uplift capacity and reduce concrete volumes; and (iii) that simple projection of the uplift failure wedge to the ground surface can lead to an overestimation of the failure wedge size. Direct comparison with centrifuge tests shows close agreement in maximum uplift capacity, although some discrepancies were observed in the displacement at the peak failure state. Nevertheless, this full-scale validation provides confidence in implementing the novel design methods for pad foundations supporting overhead electrical line infrastructure.
This study investigates the fundamental behaviour of road embankments subjected to sequential rainfall infiltration and seismic loading using a newly developed centrifuge rainfall simulator. Two model embankments with different degrees of compaction (D-c = 82% and 90%) were tested under 30G centrifugal gravitational field, followed by seismic excitation using the Kobe earthquake record. The rainfall tests reproduced pore water pressure increases at the embankment base, with lower-density embankments (CASE1, D-c = 82%) exhibiting faster infiltration and earlier rise in pore water pressure, while higher-density embankments (CASE2, D-c = 90%) showed delayed but larger increases due to lower permeability. Before seismic excitation, both cases reached comparable groundwater levels of approximately half the embankment height. Under seismic loading, CASE1 developed significant excess pore water pressure near the toe, leading to liquefaction, large deformation, and flow sliding. Maximum shear strain reached 50%, propagating from the toe to the crest. In contrast, CASE2 generated negligible excess pore water pressure, resulting instead in amplified accelerations at the embankment shoulder and limited deformation with maximum shear strain similar to 10%. These results demonstrate that embankment density governs infiltration behaviour, pore water pressure generation, and subsequent seismic deformation mechanisms.
This study investigates the influence of centrifuge container geometry on the seismic response of offshore wind turbine (OWT) jacket models with pin-pile foundations embedded in saturated sand. Two equivalent shear beam (ESB) containers, identical in design but differing in size, were employed to evaluate whether container dimensions affect coupled soil-structure interaction under dynamic loading. The older ESB container (ESB-M) was constructed using lightweight duralumin alloy rings with rubber interlayers, whereas the newer ESB container (ESB-L) utilised duralumin C-sections with rubber interlayers to achieve increased rigidity. Identical soil stratigraphy, comprising a loose sand layer overlying dense sand, and the same jacket model were adopted in both containers to ensure direct comparability. Seismic input motions were applised under two loading conditions: purely axial loading and combined axial-lateral loading. Comparative analysis of acceleration response, foundation rotation, excess pore pressure development, and amplification characteristics carried out for this study indicates that the overall seismic response trends are consistent between the two containers. Minor differences are observed in local response amplitudes, particularly under combined axial-lateral loading, reflecting variations in boundary confinement and wave propagation associated with container size. However, these differences do not alter the governing response mechanisms or behaviour, as the response remains primarily controlled by soil-structure interaction, with container geometry contributing only secondary and transient effects. Overall, the findings indicate that variations in container size do not materially affect serviceability-level response trends derived from the centrifuge tests.
This study investigates the redistribution of hoop and longitudinal stresses around cross-passage (CP) openings in shallow tunnel linings using centrifuge-scale physical modelling. Two instrumented model tunnels (parent tunnels, PT) were tested: a baseline tunnel with no opening (PT-X) and a tunnel with an opening of 50 mm dia. (PT-50). Linear strain gauges were installed at the springlines and crown of the CP in both hoop and longitudinal directions, and tests were conducted at 50 and 75 g over three cover-to-diameter (C/D) ratios under saturated soil conditions. Measured hoop strains near the springlines increased nearly linearly with C/D, rising by factors of 3.5, 2.6, and 1.78 for C/D = 0.5, 1.0 and 1.5, respectively, when comparing PT-50 to PT-X. Converting hoop strains to hoop forces and bending moments revealed that hoop forces at the springlines are amplified by 1.74-1.87 times in the presence of a CP, while bending moments remain anomalously small. Longitudinal strains at the CP springlines and crown were generally low, consistent with published numerical studies, but several longitudinal gauges recorded high readings, especially at the crown of the CP. These elevated values may be attributable to the curved tunnel geometry, installation effects, gauge misalignment, and bonding variability. Finally, this study offers a holistic set of practical recommendations for future physical modelling of CPs, addressing both instrumentation optimisation and geotechnical model design. These guidelines are intended to help future studies overcome the limitations identified here and close the identified research gaps.
This study offers insights on the possibility of using coal mine overburden as backfill material for the mechanically stabilised earth (MSE) wall through the physical model tests. The paper presents 1 g model tests of an MSE wall with three different geogrid spacings supporting a ballastless railway track, highlighting the change in stress distribution. The train loading was considered the primary destabilising force. For each geogrid spacing, five different loading conditions were considered by changing the axle load and speed of train. A reduced scale model of the MSE wall supporting ballastless railway track for high speed trains was constructed in a mild steel box of dimension 2 m & times; 2 m & times; 1.8 m. A computer controlled loading system was used to simulate the dynamic load due to the movement of the train. The results indicates that the load distributes uniformly for lesser spacing between the geogrids. The evaluated geotechnical properties of the material were found to be consistent with the requirements specified in most international guidelines for reinforced soil backfill. Furthermore, the measured track settlements and wall deformations were well within the maximum serviceability limits prescribed in relevant standards. The total wall deflection was less than 1.5 mm in all test cases.
Tapered piles installation in medium-dense Fontainebleau sand and subsequent loading were performed in the geotechnical centrifuge at Gustave Eiffel University. The physical setup includes models of piles with three different shapes – straight profile (S) and two conical with taper angles of 0.70 degrees (T1) and 1.4 degrees (T2). The aim of the study was to identify the optimal pile shape with respect to installation and load-bearing capacity. After the monotonic installation, the penetration depth and volume were the same for all pile models. Afterwards, the models were subjected to static load tests in compression and then in tension. A considerable increase in shaft friction during tapered piles installation was observed. The maximum average shaft resistance was about six and eight times higher for the T1 and T2 models, respectively as compared with the S pile. The shaft friction in compression was higher for tapered models than for cylindrical ones. Larger peak values of shaft friction in tension were also noticed for tapered piles. Similar shaft friction in tension and compression was found for cylindrical pile. On the contrary, the shaft friction ratio of tension to compression is about 0.33 and 0.14 for T1 and T2 piles, respectively.
Weak layers are commonly encountered in earth dams due to construction defects, material failures, and other factors, increasing the risk of seepage failure. Also there are few related studies. This study simulated the seepage failure process of earth dams with weak layers in a centrifugal environment. The effects of different geotextile widths, quantities, and positional arrangements on the seepage failure of earth dams with weak layers were investigated. This paper simulates weak layers by excavating a groove and filling salt, rather than by embedding perforated pipes to simulate internal defects, effectively replicating the actual stress conditions in earth dam piping channels. The tests results indicate that geotextiles can provide support to the soil above the eroded weak layer, facilitating the stable lateral expansion of piping channels. The failure time of the earth dam increases with the width and quantity of the geotextiles. However, when the weak layer is located beneath multiple layers of geotextiles, the earth dam gradually collapses.
Micropile–anchor composite structures (MACSs) are effective in slope stabilisation by combining the active resistance of anchor cables with the passive reinforcement of micropiles. However, the reinforcement mechanism of MACS under prototype conditions remains unclear, as existing studies have focused on small-scale 1-g model tests. This study conducted three centrifuge model tests on soil slopes reinforced with double-row micropiles and double/single-row MACS, respectively, based on a highway slope in Shandong, China. The development of earth pressure, pile bending moment, anchor axial force, and slope deformation was systematically analysed, and crack propagation and failure characteristics were examined. The results demonstrate that MACS significantly improve slope performance by reducing earth pressure and restricting deformation. Lateral earth pressure is redistributed between front and rear micropile rows, and load sharing is affected by reinforcement configuration. Anchor cables enhance the plastic deformation capacity of slopes and inhibit surface crack growth, while double-row micropiles obstruct sliding surface coalescence. Furthermore, micropiles row influence slope deformation at the failure stage, with double-row MACS-reinforced slopes remaining stable with minor surface cracks, whereas single-row MACS-reinforced slopes fail as crushed blocks along a circular sliding surface initiated by main cracks. These findings contribute to understanding the reinforcement mechanism of MACS.
The paper presents the design of a calibration chamber, developed for the testing of a novel self-burrowing probe for in situ soil investigation. The self-burrowing probe is currently under development at ETH Zurich, and its key components will be proof-tested in the controlled environment of the developed chamber. The design of the latter incorporates specific solutions for the testing of the probe: the chamber is equipped with a central opening at the top and base plates, enabling the probe to vertically protrude from the chamber. This aspect is useful for eliminating the tip resistance of the probe and isolating its response, which is relevant when assessing the resistance of the probe's anchoring system or, in general, for the evaluation of interface properties. The chamber allows for testing under two boundary conditions: (i) zero lateral strain or (ii) constant lateral stress. In the latter case, the radial stress is applied by water pressure inside a membrane, while a pneumatic, doughnut-shaped cushion at the base is used to impose the vertical stress. The paper outlines the key components of the chamber, the sample preparation, and the testing procedures, along with the results of the proof tests conducted in dry Perth sand.
Shared anchors for floating offshore wind turbines (FOWTs) offer potential cost savings, but their geotechnical performance under complex multidirectional mooring loads in soft clay requires better understanding. To address this, centrifuge modelling was conducted at 75 g on model suction anchors in normally consolidated kaolin clay. The experiments simulated several loading scenarios, including monotonic pull-out and multidirectional loading patterns representing shared anchor configurations (three lines at 45 degrees inclination to the horizontal plane, spaced by 120 degrees azimuthally). Three load tests were performed: a monotonic reference test and two multidirectional tests involving alternating and simultaneous line loading. Measurements included the anchor load-displacement response and excess pore pressures with complementary data from digital image correlation. The baseline monotonic test yielded an ultimate capacity of approximately 4 MN. Alternating line loading induced progressive downward displacements, while simultaneous two-line loading produced a trend of upward movement. Simultaneous loading also led to greater horizontal displacements, reflecting increased mobilisation of soil shear strength under compound loading paths. Post-multidirectional monotonic tests revealed reductions in anchor capacity between 10% and 38%, depending on the load path history and inclination. This work delivers benchmark data clarifying suction anchor behaviour under multidirectional loads to validate numerical models and optimise shared anchor designs for FOWTs.
Bucket foundations in tripod- or tetrapod-jacket structures may be subjected to sustained and cyclic uplift loading; hence, their stability under uplift loading has received attention. Model tests were conducted in the present study to investigate the performance of bucket foundations under sustained loading, with the aim of determining the critical uplift load that ensures foundation stability. The first series of model tests included monotonic and sustained uplift tests with the skirt compartment vented, aiming at investigating the reconsolidation effect on the ultimate frictional resistance along the skirt. The drainage valve was sealed in the second series of tests, such that the evolution of the frictional resistance, reverse end bearing resistance, and suction on the bucket under sustained loading could be illustrated. Moreover, the critical sustained uplift loading level is recommended based on the rate of the accumulated displacement of the bucket under sustained uplift loading, providing implications for the usage of suction in design practices.
Due to very low noise emission during installation, prefabricated concrete screw-type piles (PCSP) could potentially be viable options as foundations for offshore and onshore structures. However, little attention has been paid to the axial load-bearing behaviour in compression of this specific prefabricated screw-type pile system in comparison with conventional displacement pile systems. This article describes an experimental campaign of centrifuge tests performed at 100g on both screw-type piles and straight shafted piles (SP) with diameters of 550 and 475 mm at prototype scale. The outer screw diameter (Ds) to pile core diameter (D) ratio amounted to Ds/D = 1.25, and the screw pitch (Lp) to pile core diameter (D) ratio (pitch ratio) was selected as Lp/D = 0.57. Saturated Vingerling Clay was used to model the soil layer, and a low loading rate was selected to simulate drained conditions. Piles were installed at 1g; therefore, the pile installation process was not fully modelled. For both pile diameters investigated, the results indicate an approximately 45% higher bearing capacity with the PCSP compared with the capacity of the SP.
The large-diameter monopile is a commonly used foundation concept for offshore wind turbines. The advantages of geometrical simplicity and reliable performance make it often the most attractive solution. Despite the concept's high popularity, optimisation of the current design models can still be made. To address fundamental understanding of modelling effects in centrifuge testing of laterally loaded monopiles in sand, a large coordinated centrifuge-testing programme across nine different centrifuge centres worldwide has been conducted. This paper presents firstly the results of a local benchmark modelling of model test series performed in two centrifuges and secondly the results of global benchmark testing across the nine centrifuges. The results highlight the reliability of centrifuge testing as it was possible to model a similar prototype response in both the local and global benchmark tests, despite differences in the experimental setups and pile geometries. Furthermore, as examples of the modelling technique, two different cases are presented, one showing the effect of installation and one showing the effect of pile penetration depth. Finally, recommendations are provided to enhance centrifuge testing of monopile response under complex loading.
