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Journal articleTantivangphaisal P, Taborda D, Kontoe S,
Implementation of a practical sand constitutive model coupled with the High Cycle Accumulation framework in PLAXIS
, MethodsX, ISSN: 2215-0161 -
Journal articleTaborda D, Pedro A, Xia H, et al., 2024,
A methodology for improved predictions of surface ground movements around shafts
, Proceedings of the Institution of Civil Engineers: Geotechnical Engineering, ISSN: 1353-2618Shafts are typically employed in urban environments to provide access or ventilation to underground structures such as stations, railways or highways. The choice of design is determined, among other things, by the need to control settlements at the surface, often estimated during early design stages using empirical expressions. These have been shown to have limited accuracy, failing to account appropriately for the effect of shaft diameter on the ground movements associated with shaft excavation. This paper reviews empirical expressions available in the literature in the context of a large database of settlements induced by shaft excavation in London. A comprehensive set of detailed numerical analyses is performed to enable the development of a new set of expressions capable of predicting accurately the computed vertical and horizontal ground movements at the surface. The new expressions are shown to provide better predictions of the observed field data than predictiveexpressions available in the literature, establishing a new benchmark against which future proposals can be assessed.
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Conference paperLiu J, Tsiampousi A, Ruiz Lopez A, et al., 2024,
Assessing tunnel-structure interaction effects in London Clay
, XVIII European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: CRC Press, Pages: 614-617 -
Conference paperTantivangphaisal P, Taborda D, Kontoe S, 2024,
Numerical modelling of the long-term cyclic ratcheting of monopile foundations under lateral loading
, XVIII European Conference on Soil Mechanics and Geotechnical Engineering, Publisher: CRC Press, Pages: 3349-3352There is growing interest to utilise advanced numerical methods by industry practitioners in the predictionof the long-term response of monopile foundations under lateral cyclic loading. One framework of interest is the HighCycle Accumulation (HCA), as it can overcome the limitations of computational expense and error accumulationencountered by conventional cycle-by-cycle finite element analyses. The authors’ implementation of HCA within thefinite element package PLAXIS is presented with an emphasis on the framework’s key components and underlying assumptions. Furthermore, by coupling HCA with a practice oriented elasto-plastic model for sands, predictions using different HCA calibration approaches are evaluated against the field measurements of a medium sized cyclic lateral pile load test from the Pile-soil analysis (PISA) joint industry project.
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Journal articleLiu R, Taborda D, 2024,
A methodology for incorporating thermal interference in the design of thermo-active pile groups
, Geomechanics for Energy and the Environment, Vol: 39, ISSN: 2352-3808This paper introduces innovative practical methodologies for evaluating the thermal performance of thermo-active pile groups. First, a streamlined approach for determining G-functions within such groups, based on the G-function of a single thermo-active pile is introduced. This is accomplished through a newly introduced thermal interaction factor for G-functions quantifying the increase in temperature when a pile is subjected to thermal interference from another pile. Subsequently, the paper proposes a method for calculating the power of piles within thermo-active pile groups when subjected to transient inlet temperatures. A thermal interaction factor for power is derived, quantifying the power reduction resulting from thermal interference due to another pile operating in the vicinity. These simplified methodologies are shown to reproduce the thermal performance of pile groups simulated using three-dimensional thermo-hydraulic analyses with excellent levels of accuracy without the associated computational cost. Finally, the proposed design process is applied to a 3 × 3 thermo-active pile group subjected to transient thermal loads, yielding accurate estimations of power, G-functions, and temperature changes of the thermo-active pile group. Overall, these simplified methodologies offer a robust framework for evaluating and optimising the thermal performance of thermo-active pile systems.
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Conference paperTaborda D, Tsiampousi A, Georgiadis K, 2024,
Impact of stiffness properties and overconsolidation on the lateral behaviour of monopile foundations in clay deposits
, XVIII European Conference on Soil Mechanics and Geotechnical Engineering -
Conference paperEleftheriou E, Taborda D, 2024,
Numerical modelling of suction bucket foundations subjected to axial loading
, XVIII European Conference on Soil Mechanics and Geotechnical Engineering -
Conference paperRuiz Lopez A, Taborda D, Tsiampousi A, et al., 2024,
Applying machine learning to the development of surrogate models for shafts in clay
, XVIII European Conference on Soil Mechanics and Geotechnical Engineering -
Journal articleWen K, Kontoe S, Jardine R, et al., 2024,
Finite element modelling of pipe piles driven in low-to-medium density chalk under monotonic axial loading
, Computers and Geotechnics, Vol: 172, ISSN: 0266-352XPercussive driving in low-to-medium density chalk creates a thin annulus of fully de-structured ‘putty’ chalk around pile shafts and an outer annular zone where fracturing is more intense than in the natural chalk. This damage and the related generation, and subsequent equalisation, of excess pore pressures impacts the piles’ time-dependent axial loading behaviour, as do other ageing processes. This paper presents finite element analyses of open steel tubular piles driven for the recent ALPACA and ALPACA Plus research projects under monotonic axial loading to failure after extended ageing periods. A nonlinear elastic stiffness model with a nonlocal deviatoric strain-based Mohr-Coulomb failure criterion was employed, with different sets of properties to represent the de-structured, fractured chalk and intact chalk. It is shown that the piles’ axial responses are mainly controlled by the puttified chalk annuli. A simplified but efficient means is adopted to impose pre-loading chalk effective stress conditions that explicitly capture the effects of installation damage and subsequent ageing. The potential for strain-softening in the brittle chalk is examined and the effective stress paths developed in representative chalk elements throughout the loading are considered in conjunction with the mobilisation of accumulated deviatoric strains. The simulations indicate 264% higher shaft capacity in compression than in tension, which is mainly attributed to the internal chalk plug.
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Conference paperMA S, Kontoe S, Taborda D, 2024,
Layered system response effects of liquefiable deposits
, 8th International Conference on Earthquake Geotechnical Engineering, Publisher: The Japanese Geotechnical Society, Pages: 848-853Simplified liquefaction assessment procedures have been widely used to estimate the severity of liquefaction under earthquake loading, which is often confirmed by the presence of sand boils. Back analyses of case studies have shown that the simplified assessment procedures can overestimate or underestimate the liquefaction potential of a deposit (i.e. false positives and false negatives respectively). The occurrence and severity of sand boils are highly dependent on the soil permeability and the hydro-mechanical interaction of cross-layers (system response effects), which the simplified liquefaction assessment procedures do not account for. Additionally, the variation of hydraulic conditions during and after the earthquake shaking significantly affects the evolution of sand boils. In this study, the layered system effects on liquefiable deposits are examined through dynamic nonlinear effective stress analysis. Scenarios where a liquefiable layer is interbedded within materials of distinct hydro-mechanical characteristics are examined parametrically employing the fully coupled (u-p) finite element software PLAXIS. The influence of the presence and the characteristics of non-liquefied or low-permeability layers surrounding the liquefiable layer on the development of sand boils is investigated.
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Journal articlePedro AMG, Taborda DMG, 2024,
Dataset on the behaviour of the Areolas da Estefania formation in Lisbon and its modelling using a state-dependent soil model
, Data in Brief, Vol: 54, ISSN: 2352-3409Experimental and computational data are presented for Areolas da Estefania, a geomaterial which is crucial for the development of the underground infrastructure of the city of Lisbon, Portugal. The experimental data comprise the particle size distribution of the material and measurements obtained during a series of strain-controlled triaxial compression tests performed on intact samples. The behaviour of this material at a wide range of strains, under constant mean effective stress levels of 130 kPa, 300 kPa and 400 kPa is established, with the presented dataset containing information on stress (mean effective stress and deviatoric stress) and strain states (axial strain and volumetric strain). These are complemented by the results of bender element tests imposing vertically-travelling waves for characterisation at very small strains. Complementarily, the computational dataset establishes a reference reproduction of the response of Areolas da Estefania using a material model which combines a non-linear small stiffness formulation with a state-dependent strength and plastic dilatancy. Overall, this dataset can be used as a reference when assessing the behaviour of other samples of Areolas da Estefania or comparable materials, or when evaluating constitutive models for granular geomaterials.
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Journal articleTsiampousi A, 2024,
A three-dimensional study of vegetation management on cut slopes
, Canadian Geotechnical Journal, ISSN: 0008-3674Infrastructure slopes often become covered in dense vegetation due to poor vegetation management. Despite increasing cohesion and enhancing slope stability, trees lead to serviceability problems, primarily towards the end of the summer. Drastic approaches, however, such as vegetation clearance, have caused instabilities during wet seasons. Therefore, appropriate, effective, and continuous vegetation management is of essence and should consider both biodiversity and the engineering asset, while accounting for the contribution of vegetation in battling climate change. Developing numerical methodologies and models can be particularly useful in acquiring insight into the complex mechanism and processes taking place during slope-plant-atmosphere interactions. The work presented here focused on the development of a 3D numerical model to investigate different vegetation management strategies for a slope covered in trees and suffering serviceability problems. Different 3D patterns of tree removal and of replacement of trees with shrubs were considered and the effect of each of these on the serviceability and stability of the slope during the subsequent year was examined. The results demonstrated that replacement was preferable to removal, as stability and serviceability should be considered concurrently, and that, occasionally, clearance may have detrimental effects non only on stability but also on serviceability.
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Journal articleLiu R, Taborda DMG, 2024,
The effects of thermal interference on the thermal performance of thermo-active pile groups
, Renewable Energy, Vol: 225, ISSN: 0960-1481Thermo-active piles are extensively utilised for providing low carbon heating and cooling to buildings and are a key technology to help fulfilling sustainability targets. However, when deployed as a group, thermal interference between neighbouring piles can significantly impact the overall thermal performance of the system. This study first explores the lower and upper bounds of thermal interference by comparing the thermal performance of a single pile with that of infinitely-large thermo-active pile groups. A simplified method is subsequently proposed to quantify the effects of thermal interference and estimate the thermal performance of thermo-active piles arranged in realistic group geometries. This method involves deriving thermal interaction factor curves that represent the penalty on the thermal performance of a pile due to the presence of another pile in its vicinity. By applying the principle of superposition, the penalty on the thermal performance of any pile within any group can be calculated using these thermal interaction factor curves. The accuracy of the simplified method is validated through comparisons with numerical analysis, demonstrating its ability to estimate accurately the thermal performance of 2 × 2 and a 3 × 3 thermo-active pile groups, regardless of the pile diameter considered.
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Conference paperMoller J, Kontoe S, Taborda D, et al., 2024,
Assessment of a constitutive model for simulating the post-liquefaction response of sands
, 8th International Conference on Earthquake Geotechnical EngineeringAdvanced constitutive models can be used to simulate the effects of soil liquefaction on foundations and buildings in dynamic Finite Element analyses. While various constitutive models have been applied in numerical studies considering one-time cyclic loading, there remains a need to investigate their performance for repeated cyclic loading events. Deposits in seismic areas are likely to be subjected to multiple consecutive earthquakes and aftershocks. However, the impact of the previous shaking history on the cyclic resistance of the soil and its post-liquefaction static response is the subject of ongoing research and is not yet fully understood. Based on findings from experimental studies, this paper presents an assessment of a constitutive model and its ability to capture the effects of the loading history on the sand response. This involves the simulation of laboratory element tests for different cyclic loading, reconsolidation and monotonic shearing series. A particular focus lies on model features incorporated to simulate cyclic mobility at low effective stress levels, as well as the anisotropic post-liquefaction response of the material.
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Conference paperKontoe S, Moller J, Taborda D, 2024,
Seismic response of offshore foundations with emphasis in liquefiable ground conditions
, 8th International Conference on Earthquake Geotechnical EngineeringFollowing the rapid expansion of offshore wind farms in seismic areas, this study examines the hurdles encountered when applying conventional seismic evaluation methods, originally devised for onshore structures, to offshore installations. This includes the assessment of liquefaction offshore at large depths and its consequences on the response of offshore wind turbines supported by monopile foundations. With the aid of 3D dynamic finite element analysis of the entire SSI system (tower, monopile foundation and soil domain), it is shown that the resonant frequencies of the examined 5MW turbine were excited for the considered ground motion, inducing significant nonlinearity in the soil surrounding the monopile foundation. The vertical seismic motion, often overlooked in seismic design, is also discussed as it bears significance for the response of offshore wind turbines. Simple site response analysis for vertical ground motion emphasizes the need to consider the entire water column and soil profile depth to the bedrock for an accurate representation of the soil-water system's compression natural frequency in offshore environments.
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