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.

This paper presents data from an initial development stage of an ‘umbrella anchor’ concept. The anchor can be pushed into a sand deposit in a folded arrangement to reduce installation loads. When a pull-out load is applied to the mooring line, the anchor deploys to create a large embedded plate anchor. Physical modelling was carried out in a saturated sand bed with the anchor installed at depths of up to 1.6 m and loaded vertically. During installation, liquefaction was generated at the tip of the anchor to reduce the penetration resistance. This enabled the anchor to be installed quickly and accurately to a target depth. The anchor could provide pull-out resistances comparable to an anchor that has been wished-in-place at similar depths. The observed behaviour provided encouraging preliminary results and suggests that, with further development and analysis, the concept could potentially be used for commercial applications.

Large fixed vertical offshore wind turbine (OWT) tower structures are typically used to transfer complex loads to the foundations from a combination of wind, waves, and self-weight. These loads must be accommodated within a very small rotation envelope and natural frequency bands to allow the turbines to operate effectively. These challenging loading conditions and strict operational requirements can lead to extremely costly foundation de-signs. Several foundation options are available to support these turbines, with monopiles currently accounting for 80% of the installed capacity with routinely used diameters of 5-8 m and depths of penetration of 30-80 m. To limit monopile diameters and penetration depths, an improved monopile design: the 'hybrid foundation' comprising a plate and centrally located pile, is proposed as an alternative to monopiles. A series of scaled physical model centrifuge tests were conducted to investigate the benefits of the hybrid foundation system and compare its behavior with the typically used monopiles. This type of foundation system can enhance the per-formance of an OWT since the turbines are subjected to high lateral loads and overturning moments. Centrifuge modeling has been used to investigate the lateral capacity and stiffness of the foundations under lateral monotonic and cyclic loading conditions. Two models were tested: a standard monopile (MP) and a hybrid foundation (HF). Lateral loads were applied with eccentricity for both models to replicate prototype (field) conditions. Models were tested at 50g in over-consolidated clay beds. These soil samples were prepared using inflight consolidation and subjected to a sand surcharge, to increase the shear strength in the zone of influence of the model foundations. Monotonic lateral loading results indicated that the addition of a plate improves the relative lateral ultimate capacity, whilst enabling a reduction of monopile penetration depth and diameter for similar capacities. Specifically, similar capacity/stiffness was realized for the HF system compared to the MP. One-way cyclic lateral loading indicated both the HF and the MP had a shakedown response under fatigue loading of up to 10000 cycles, which indicates the potential use of this novel system for future developments.

One of the ways to install plate anchors in deep seabed is to drop the anchor system from the sea level and allow it to initially embed in the seabed under its own weight. Further dragging would cause the anchor to rotate and embed further into the seabed. There could be difficulties of getting the anchor plate horizontal or mooring line to be perpendicular to the plate where the maximum pullout capacity could be achieved. As part of the investigations, various aspects of the plate performance were examined through centrifuge testing in which the plate orientation and pullout angles were varied. It was presumed that dynamic stability of the anchor (during field installation) can be achieved by having the plate in biwing configuration. Therefore, the performance of the biwing anchors having different spacing between the plates was also examined in the centrifuge testing program and the findings were compared with predictions obtained through finite-element modeling (FEM). Both pullout directions and the plate angles considerably influenced the pullout capacity factors. The comparison between the predicted pullout capacity using FEM and measured pullout capacity for biwing anchors at shallow embedment depths was excellent. However, the FEM-predicted pullout capacity was noticeably lower than the measured ones for deep anchors. Pullout capacity of biwing anchors at shallow embedment depth increased as the spacing between the plates S increased from 0 to 0.5B. However, there appears to be a slight reduction in the performance in deep embedment anchors. This is also reflected in FEM findings.

Offshore Wind Turbines (OWT) with increasingly higher energy output are being developed to meet energy demands, posing greater challenges for their foundation design. Several foundation types are used to support these turbines, with monopiles (MPs) accounting for 80% of the installed capacity. In this study, three-dimensional (3D) nonlinear finite element models (FEM) were employed to investigate the behaviour of a monopile foundation supporting a 5MW wind turbine subjected to lateral loading. The results indicate that the MP behaviour depends on the pile length to diameter (L/D) ratio and the soil shear strength. Inspection of the bending-moment profiles at the lateral ultimate capacity indicated that the monopiles can behave in a flexible manner, even with low L/D ratios. The L/D ratio affected the MP normalized lateral ultimate capacity to varying degrees, and the biggest effect was for soft clays, amounting to an approximately five-fold increase for L/D values of 3.33 to 13.33. Lesser effects were found for stiff clays.

Many available ground improvement techniques are effective, but involve large amounts of carbon dioxide emissions. Any green ground improvement technique would thus be beneficial. In this work, dry air, supplied at low pressure and relative humidity, was used to remove water from a soft soil deposit. The investigation was carried out at model scale, with a soft soil layer formed in a box of size 1.0 × 1.0 × 0.75 m. The soil bed was fitted with slender granular columns for the injection of dry air. The technique is the reverse process of vacuum consolidation, in which the magnitude of negative pore water pressure that can be applied to the soil is limited and thus requires careful construction procedures. The dry-air approach is simple and does not require any complex construction procedures. The investigations carried out over a limited period showed a significant improvement in the strength of the soil bed, indicating possible full-scale implementation. Full-scale implementation of the technique may not require any new construction methods as the procedure is very similar to that adopted in vacuum consolidation. However, variabilities in ground conditions, including the groundwater table, may pose additional challenges and supplementary information (soil–water characteristic data and numerical modelling) may be necessary to implement this technique at full scale.

All discretized numerical models contain modeling errors – this reality is amplified when reduced-order models are used. The ability to accurately approximate modeling errors informs statistics on model confidence and improves quantitative results from frameworks using numerical models in prediction, tomography, and signal processing. Further to this, the compensation of highly nonlinear and non-Gaussian modeling errors, arising in many ill-conditioned systems aiming to capture complex physics, is a historically difficult task. In this work, we address this challenge by proposing a neural network approach capable of accurately approximating and compensating for such modeling errors in augmented direct and inverse problems. The viability of the approach is demonstrated using simulated and experimental data arising from differing physical direct and inverse problems.

: A new approach in landfill liner design which combines hydraulic containment of leachate with contaminant attenuation to improve the performance of these environmental control systems at landfills is described. The idea is to re-use readily available industrial waste residues (construction and biomass waste) as additives for natural clay liners, wherein the additives have specific properties which enhance the attenuation of contaminants by the mixture. The aim is to (1) evaluate the contaminant attenuation capacity of these mixtures, (2) develop design guidelines to construct liners for waste containment systems and similar applications, and (3) interpret their performance using numerical modelling. This is evaluated in permeation studies using a geotechnical centrifuge, which enables the performance of liner compositions to be tested for representive time-scales (100 years), pressures and temperatures at realistic experimental time-scales of days-weeks in the laboratory. The permeation experiments include liner compositions flushed with leachate to deduce contaminant transport and attenuation mechanisms, followed by rainwater to assess the potential for release of attenuated contaminants. This experimental methodology is illustrated with depth profiles from permeation studies conducted on different clay-additive compositions. The concept will be applicable for liner design at other waste disposal facilities and is a timely improvement which addresses the problem of managing large quantities of industrial residues. Instead of disposal these can be recycled as an additive in host clay to construct these liners, thus conserving natural resources (clay) and reducing construction costs. It also provides an effective and more environmentally sustainable basis to reduce risks from leachate leakage.

Engineered synthetic liners on their own cannot protect the environment and human health against landfill leachate pollution. Despite their initial impermeability, they are susceptible to failure during and after installation and have no attenuation properties. Conversely, natural clay liners can attenuate leachate pollutants by sorption, redox transformations, biodegradation, precipitation, and filtration, decreasing the pollutant flux. Depending on the clay, significant differences exist in their shrinkage potential, sorption capacity, erosion resistance and permeability to fluids, which affects the suitability and performance of the potential clay liner. Here, the physico-chemical, mineralogical and geotechnical characteristics of four natural clayey substrata were compared to discuss their feasibility as landfill liners. To study their chemical compatibility with leachate and rainwater, hydraulic conductivities were measured every ≈2 days spread over 7 weeks of centrifugation at 25 gravities. At field-scale, this is equivalent to every 3.4 yrs spread over 80 yrs. All the clayey substrata had favourable properties for the attenuation of leachate pollutants, although different management options should be applied for each one. London Clay (smectite-rich) is the best material based on the sorption capacity, hydraulic conductivity and low erodibility, but has the greatest susceptibility to excessive shrinkage and alterable clay minerals that partially collapse to illitic structures. Oxford Clay (illite rich) is the best material for buffering acid leachates and supporting degradation of organic compounds. The Coal Measures Clays (kaoline-rich) have the lowest sorption capacity, but also the lowest plasticity and have the most resistant clay minerals to alteration by leachate exposure.

Daily precipitation in Japan is currently increasing. River levees are constructed by compacting various natural materials. Internal erosion can be induced by suffusion, in which fines within the soil skeleton are transported to the toe of levee or outside the levee in an accordance with seepage flow. There are very few studies that refer to the effects of internal erosion on macro deformation and the instability of a levee. In this study, modeling tests of a levee were carried out to simulated floods in a 30g centrifugal field. Two types of material were prepared based on Kenny’s diagram, one classified as “stable” and the other as “unstable”. For stable soil, surface erosion could be observed on the landside of the levee. When the flood level was increased to overtop the crest, the levee caused catastrophic failure. Whereas, for unstable soil, tension failure was observed the toe, whereby, catastrophic larger circular slip was able to be confirmed.

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 program across 11 different centrifuge centres worldwide is ongoing. This extended abstract presents the initial results of global benchmark testing.

This paper discusses the development and implementation of an educational module, which incorporates a state-of-the-art teaching centrifuge into open-house demonstrations and the undergraduate educational pedagogy. The students' activities within the developed module are centred on building a model consisting of a mechanically stabilized earth (MSE) retaining wall. The students are exposed to basic educational theory to calculate the capacity of an MSE wall system which is verified through a design and build experimental modelling programme. Results obtained are compared with theoretical predictions and numerical limit equilibrium solutions for a variety of design inputs. These include different numbers of reinforcement layers, thicknesses and widths of reinforcement, and the length of reinforcement versus the surface surcharge position to consolidate their understanding of MSE design variables.

A series of centrifuge cyclic monopile lateral loading experiments in dry sand are presented. Model foundation tests were performed at 100 gravities (100g) of a prototype pile 5m in diameter with an embedment depth of L/D= 5. Observations indicate that permanent rotational failure criteria (theta at mudline equal to 0.25 degrees) may not be reached for load magnitudes 40% or less of the monotonic failure load for 10(7) cycles. A cyclic degradation model for monopile rotation accumulation is also presented. Results from the cyclic tests are used to plot contour lines of predicted rotations based on load magnitude and number of cycles applied. This model is then used to predict cyclic rotational accumulation of a load magnitude ramp test and appears to perform well.

This paper describes preliminary tests from a ‘transparent soil permeameter’ that has been developed to study the mechanisms that occur during internal erosion in filter materials for embankment dams. The laboratory-based experiments utilise an optical approach where glass particles are used in place of soil, and optically matched oil is used in place of water. The refractive index matching of the fluid and solid enables a two-dimensional “slice” or plane of particles and fluid to be viewed inside the permeameter, away from its walls via a laser sheet and captured by digital camera. The developed set up has already been tested and showed that optically matched glass and oil can behave similarly to soil and water materials as used in previous laboratory testing. In this study we present a flow characterization within a refractive index matched medium made of glass beads. To this end a small amount of fluid tracers is seeded inside the fluid and the velocity field inside the porous media is obtained using PIV measurements.

This paper outlines the design and development of a rainfall simulator for the centrifuge for the purpose of evaluating infrastructure resilience in changing climate conditions. Pressure losses in the water supply system are evaluated and related to nozzle pressure and flow rate at both 1 g and elevated gravity up to 100 g. Coriolis effects are investigated and quantified with increasing gravity accounting for effects of air flow through the experimental package on the University of Sheffield 50 gT beam centrifuge. The rainfall simulation capabilities are demonstrated on a slope boundary problem to validate the developed system. Slope deformation is captured using digital image correlation techniques which confirm triggering of slope movements with applied rainfall events.

Monopile supports are to this day the preferred foundation solution for offshore wind turbines. There is still an empirical gap, however, between the in-situ conditions for these monopiles and the test conditions the current design methods are based on.This relates to both pile geometry and load conditions. The gap introduces uncertainties and in order to optimise design, this gap needs to be minimised. Scaled modelling in an increased acceleration field, i.e. testing in a geotechnical centrifuge, can be an effective way of understanding behaviour and obtaining empirical evidence. Reliable testing is underpinned by thorough consideration of scaling laws. To address fundamental understanding of modelling effects in centrifuge testing of laterally loaded monopiles in sand, a review of the latest relevant research for performing state of the art centrifuge testing of monopiles in sand has been carried out. Based on this review, modelling effects that introduce some uncertainties in the scaling of the results are identified, and based on that, a coordinated centrifuge-testing program is presented. The test program will be performed across five centrifuge facilities and aims at minimising the identified modelling uncertainties.

Centrifuge model tests of buried flexible pipes in dry sand subjected to surface traffic loads are presented. Model pipe tests were performed at 25 gravities (25g) of a prototype pipe 355 mm in diameter. Pipe behaviour was observed for different burial depths of 0.5, 0.75, 1.0 and 1.5 m; and load eccentricities of 1 and 2 pipe diameters. Results show that pipes buried at shallower depths are subjected to significantly greater bending moments and corresponding shear stresses. When the load is applied at an eccentricity, if the pipe remains within the zone of stress influence, a comparable magnitude of maximum moment is anticipated. An initial series of 20 cycles were also carried out. Results indicate an amount of ‘locked-in’ bending moment upon unload; a phenomenon more evident for the shallower buried pipe.

The significant amount of image data that can be generated during physical model tests can provide a useful alternative and direct route to determining the stress-strain response characteristics of the soil used in the model without recourse to e.g. sampling and triaxial testing. This paper builds on previous work that has shown how using external loading data and Particle ImageVelocimetry (PIV) derived full-field displacement data allows the use of optimisation to reconstruct the stress-strain curve of the soil body in a piecewise manner. In this paper the technique is applied to both artificial and physical plane strain test scenarios to illustrate the potential of the method and discusses some of its advantages and challenges, particularly with respect to handling imperfect or noisy physical test data.