Publications
48 results found
Ruiz Lopez A, Tsiampousi A, Standing J, et al., 2024, A new model for simulating the behaviour of grey cast iron tunnel joints with structural elements in geotechnical analysis, Engineering Structures, Vol: 304, ISSN: 0141-0296
Recent developments have demonstrated that the behaviour of segmental grey cast iron (GCI) tunnel linings can be simulated accurately with sophisticated 3D numerical models where the geometry of the segments and joints is considered explicitly. Such a 3D model is, however, impractical for geotechnical numerical analyses where the tunnel lining is usually simulated with simpler, structural elements. In this paper, a novel tunnel joint model specifically developed for simulating the behaviour of GCI longitudinal joints with beam elements in geotechnical finite element analysis is introduced. Unlike existing models, the model considers the contribution of the bolts to the joint response and the nonlinear decay of the rotational stiffness after joint opening as well as the dependency on the compression level. After calibration of the model parameters, the model was utilised in a series of parametric analyses replicating the elastic continuum model using 2D beam elements. The response of the segmental GCI lining was essentially equivalent to that predicted by an advanced 3D model which validated the new modelling approach. The development of the joint beam model enables the nonlinear behaviour of segmental GCI tunnel linings to be accounted for in routine geotechnical numerical analyses.
Kirkham A, Tsiampousi A, Potts D, 2024, Thermo-mechanical calibration of a temperature-controlled oedometer, Geotechnical Testing Journal, ISSN: 0149-6115
Tsiampousi A, Day MC, Petalas A, 2024, Engineering soil barriers to minimise annual shrinkage/swelling in plastic clays, Geomechanics for Energy and the Environment, Vol: 38, ISSN: 2352-3808
Engineered soil barriers have been proposed to prevent rainwater infiltration into the underlying soil, thus improving stability of sloping ground. The use of engineered barriers on flat ground as means of preventing flooding has also been explored. This paper aims to provide proof-of-concept as to the potential efficiency of engineered barriers in minimising soil shrinkage and swelling arising from seasonal variations of water content and pore water pressures within the ground due to its interaction with the atmosphere. A series of 2-dimensional, hydro-mechanically coupled finite element analyses were conducted to this effect. Emphasis was placed on accurately modelling the stiffness of the underlying soil, accounting for its small-strain behaviour, as well as the hydraulic behaviour of all the layers involved. The results confirm that it is possible to engineer barriers to minimise shrinkage/swelling in greenfield, as well as urban, conditions and highlight the influence of barrier geometry and configuration, so that recommendations for the design of such barriers can be made.
Ruiz López A, Tsiampousi A, Standing JR, et al., 2023, The influence of tunnel joints on the present-day condition of a grey cast iron tunnel, Computers and Geotechnics, Vol: 164, Pages: 1-18, ISSN: 0266-352X
The present-day condition of a grey cast iron (GCI) tunnel was investigated numerically by means of a series of plane-strain geotechnical analyses that focused on establishing the influence of the modelling approach adopted to simulate the behaviour of longitudinal tunnel joints. The GCI tunnel lining was simulated in three different ways: (i) as a continuous lining; (ii) as a jointed lining adopting a simple joint model that neglects the presence of the joint bolts and (iii) as a jointed lining adopting a more sophisticated model that considers both the nonlinear response of the joint after opening and the contribution of the bolts to the ultimate capacity. The numerical results demonstrate that accounting for the tunnel joints has a considerable impact on the tunnel response. Significant differences are also observed in the results obtained with the two joint models, hence demonstrating the practical significance of employing an advanced model able to reproduce accurately the rotational behaviour of the joint. The drainage behaviour of the joints was also investigated and the numerical results indicate that drainage even through only the knee joints causes significantly more soil consolidation than that from a watertight tunnel and consequently, larger tunnel deformations and forces.
Kirkham A, Tsiampousi A, Potts DM, 2023, Thermo-mechanical behaviour of a kaolin-based clay soil, Geotechnique: international journal of soil mechanics, ISSN: 0016-8505
The thermal behaviour of KSS, a low plasticity artificial clay made with kaolin clay, silt, and sand, was investigated in a series of temperature-controlled oedometer tests, at temperatures between 5 °C and 70 °C, and at vertical pressures up to 2.4 MPa. The experiments investigated the effect of over-consolidation ratio (OCR), pressure level, and repeated thermal cycling on thermally-induced volume change. Thermal volumetric strains were found to be dependent not only on OCR but also on pressure level, contradicting previous experimental findings and highlighting the importance of even a small dependency of compression index Cc on temperature. Furthermore, thermal volumetric strains were irreversible on heating and cooling even for highly over-consolidated samples. Although irreversibility at high OCR values has been attributed to particle rearrangement and plastic accommodation in the past, an alternative explanation is put forward here, as yielding on the Hvorslev surface is expected to occur on unloading under 1D conditions. The tests also revealed evidence of thermal creep for the initially normally-consolidated samples. The effect of both current temperature and temperature history on the reloading response of mechanically over-consolidated KSS was tested and quantified in terms of their effect on the measured pre-consolidation pressure. The results from these tests were compared to results from the available literature referring to clays of similar and higher plasticity and the comparison highlighted that although soil plasticity can explain the observed quantitative differences between high plasticity soils to a large extent, mineralogy, in addition to structure, may also play an important role for low plasticity soils.
Ruiz López A, Tsiampousi A, Standing JR, et al., 2023, Numerical characterisation of the rotational behaviour of grey cast iron tunnel joints, Computers and Geotechnics, Vol: 159, Pages: 1-17, ISSN: 0266-352X
The structural assessment of segmental grey cast iron (GCI) tunnel linings to nearby construction is challenging due to the presence of the joints affecting the stiffness of the tunnel lining. This paper presents an extensive investigation, using 3D finite element (FE) analyses, into the bending moment-rotation (M-θ) behaviour of two GCI tunnel joint geometries. These two geometries correspond to standard running and station tunnels of the London Underground network. The contribution of this study is two-fold. i) The novel characterisation of the M-θ response enables the development of new models for simulating the mechanical response of GCI tunnel joints with structural elements which can be used in simplified, 2D geotechnical analysis for tunnel safety assessments. ii) The analyses provide insight into the behaviour of GCI tunnel linings that would be difficult to achieve through experimental and field observations alone. More specifically, the analyses show that when the bolts are removed from the joints the possibility of tensile failure can be disregarded; that the initial bolt preload influences the rotational stiffness only after some rotation has taken place and does not alter the bending moment of opening; and that the out-of-plane displacement restraint has little influence on the joint response.
Tsiampousi A, 2023, 3D effects of soil-atmosphere interaction on infrastructure slope stability, 8th International Conference on Unsaturated Soils
Tsiampousi A, 2023, The importance of permeability in modelling soil-atmosphere interaction, 8th International Conference on Unsaturated Soils
Pedone G, Zdravkovic L, Potts D, et al., 2023, Numerical modelling of unsaturated MX-80 bentonite subjected to two different hydration paths and subsequent loading to high-pressures, 8th International Conference on Unsaturated Soils
Petalas AL, Tsiampousi A, Zdravkovic L, et al., 2022, Numerical investigation of the performance of engineered barriers in controlling stormwater runoff, Geomechanics for Energy and the Environment, Vol: 32, Pages: 1-15, ISSN: 2352-3808
In this paper, 2-dimensional, hydro-mechanically coupled finite element analyses are conducted to assess the performance of an engineered barrier, constructed from natural geomaterials, aimed at reducing flood risk in urban environments. The barrier consists of an unsaturated compacted soil layer with water holding properties and a drainage layer of a coarse granular material, that acts as a capillary break, and is constructed on top of the natural soil, in this case London clay. The barrier is vegetated so that its water storage capacity is renewed after each rainfall event. Sophisticated boundary conditions are used to simulate the effect of precipitation and evapotranspiration. The evolution of the rainfall infiltration and runoff rate is simulated both for a treated soil column with an engineered barrier and an untreated one consisting solely of in-situ London Clay. The percolation rate of rainfall water from the bottom of the barrier is also estimated. This comparison highlights the effectiveness of the engineered barrier in reducing the risk of fast flooding, in preventing excessive deformations and in protecting underground infrastructure during wetting and drying cycles. The effect of the hydraulic properties and geometry of the barrier is investigated by means of an extensive parametric analysis. Finally, recommendations for the design of barrier systems are made.
Tkahashi H, Zdravkovic L, Tsiampousi A, et al., 2022, Destabilisation of seawall ground by ocean waves, Geotechnique: international journal of soil mechanics, ISSN: 0016-8505
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. Nonetheless, 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. Additionally, of the possible causes of failure, the following three were identified in the current study: increased unit weight and reduced suction from wetting; enhanced seepageforce 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.
Pedone G, Tsiampousi A, Cotecchia F, et al., 2022, Coupled hydro-mechanical modelling of soil-vegetation-atmosphere interaction in natural clay slopes, Canadian Geotechnical Journal, Vol: 59, Pages: 272-290, ISSN: 0008-3674
Soil-vegetation-atmosphere interaction is long known to induce significant pore pressure variations at shallow depths and associated superficial slope movements. Recent findings suggest that the effect of this interaction may also extend to large depths in natural clay slopes. Multiple examples of weather-induced deep landslide mechanisms can be found in the Southern Apennines (Italy), where slopes are often formed of fissured clays. The relationship between the activity of these landslides and the hydro-mechanical processes due to soil-vegetation-atmosphere interaction was investigated herein by means of a two-dimensional coupled hydro-mechanical finite element analysis. A constitutive model capable of simulating the behaviour of highly overconsolidated clays, in both saturated and unsaturated states, was adopted in the analysis, in conjunction with a boundary condition capable of reproducing the combined effects of rainfall infiltration, evapo-transpiration and run-off. The results of the analysis corroborate the connection between weather conditions, pore pressure variations and slope movements in natural clay slopes. The importance of reproducing adequately the geological history of a natural slope in order to define its current state is also demonstrated.
Ruiz Lopez A, Tsiampousi A, Standing J, et al., 2022, Numerical investigation of a segmental grey cast iron tunnel ring: validation with laboratory data and application to field conditions, Computers and Geotechnics, Vol: 141, Pages: 1-19, ISSN: 0266-352X
The structural response of a segmental grey cast iron (GCI) tunnel lining ring under distortion was investigated by means of finite element (FE) analysis. Building on previous experimental investigations, a 3D numerical model, capable of reproducing accurately the behaviour observed in the laboratory, was developed with the aim of providing guidelines for the structural assessment of GCI linings in engineering practice. A comprehensive validation of the segmental ring model with the laboratory data was first completed. Subsequently, a parametric study was conducted using a set-up that replicated the widely adopted elastic continuum method, so that differences between the numerical and the analytical solution could be attributed to the presence of the longitudinal joints. In this manner, the influence of the joints on the ring response was quantitatively established and recommendations for routine engineering calculations developed. A set of bending stiffness reduction factors are proposed as a function of the tunnel ovalisation, providing upper and lower limits of the bending stiffness, as well as a global reduction factor which is an average measure of the bending stiffness reduction. These factors can be integrated into the calculation procedure of closed-form solutions in order to account for the segmental nature of GCI linings.
Petalas A, Tsiampousi A, Zdravkovic L, et al., 2021, Numerical investigation of the performance of engineered barriers in reducing flood risk, 3rd Pan-American Conference on Unsaturated Soils
Lopez AR, Tsiampousi A, Taborda DMG, et al., 2021, Numerical investigation into time-dependent effects on short-term tunnelling-induced ground response in London Clay, 10th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground (IS-Cambridge), Publisher: ROUTLEDGE, Pages: 597-604
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Kirkham A, Tsiampousi A, Potts D, 2020, Development of a new temperature-controlled oedometer, 2nd International Conference on Energy Geotechnics (ICEGT 2020), Publisher: EDP Sciences, Pages: 1-7
A new temperature-controlled oedometer has been designed at Imperial College London and commissioned to investigate the thermo-hydro-mechanical behaviour of soils. Under oedometric conditions, temperature can be varied between 5°C and 70°C, by submerging the specimen in a temperature-controlled water bath. This temperature range is appropriate for the proposed applications of the research: design of ground-source heating/cooling systems, and design of geological disposal facilities for nuclear waste. In this paper, an overview of the new equipment is given: its design, development, and calibration. First, the literature on temperature-controlled oedometer schemes is reviewed. A description of the equipment follows, with further details on the innovations and limitations of this design. As the equipment has been modified and improved over the course of the research, so too has the calibration procedure. These developments are discussed, again with the focus on innovations and limitations. Finally, a test programme and preliminary results are presented, for saturated KSS, an artificial mixture of kaolin clay, silt, and sand. These include isobaric (constant-pressure) heating tests, for a variety of loading histories. Over-consolidation ratio is found to affect the thermally-induced volume change.
Ghiadistri GM, Zdravkovic L, Potts DM, et al., 2020, Overview and conceptual constitutive framework for pellet-based buffer materials, 4th European Conference on Unsaturated Soils (E-UNSAT), Publisher: E D P Sciences, ISSN: 2267-1242
Buffer materials for nuclear waste disposal applications generally consist of blocks made of highly expansive compacted clay. However, high-density pellets of bentonite are being evaluated as an alternative buffer material for waste isolation. The material response of pellet-based buffers may be quite different from that of compacted buffers, because of the peculiar discontinuous porosity presented. An overview of the literature available on pellet-based buffers is presented and, in particular, two main topics are discussed: firstly, the characteristics of the fabric of the pellets that can be observed through techniques of micro-structural investigation, secondly, the most important behavioural features that can be seen during material testing. Additionally, the constitutive frameworks that have already been developed specifically for pellets are also reviewed. The overall objective of the paper is to highlight the differences between compacted and pellet-based bentonite buffers, in order to propose suitable assumptions to start developing a constitutive model for the latter.
Tsiampousi A, Zdravkovic L, Potts DM, 2020, Effect of hydraulic parameters on the computed serviceability of infrastructure slopes, 4th European Conference on Unsaturated Soils (E-UNSAT), Publisher: E D P Sciences, ISSN: 2267-1242
Atmospheric phenomena such as rainfall and evapotranspiration contribute to slope movements in unsaturated soils, the study of which requires fully coupled numerical methods, combined with realistic boundary conditions and appropriate mechanical and hydraulic soil properties. This paper focuses on the effect of the hydraulic behaviour, and in particular of the modelling of the soil-water retention curve and the permeability on slope movements, with the aim of identifying which model parameters are critical and, therefore, require careful experimental identification.
Cui W, Tsiampousi A, Potts D, et al., 2020, Numerical modelling of time-dependent thermally induced excess pore fluid pressures in a saturated soil, Journal of Geotechnical and Geoenvironmental Engineering - ASCE, Vol: 146, Pages: 04020007-1-04020007-15, ISSN: 0733-9410
A temperature rise in soils is usually accompanied by an increase in excess pore fluid pressure due to the differential thermal expansion coefficients of the pore fluid and the soil particles. To model the transient behaviour of this thermally induced excess pore fluid pressure in geotechnical problems, a coupled THM formulation was employed in this study, which accounts for the non-linear temperature-dependent behaviour of both the soil permeability and the thermal expansion coefficient of the pore fluid. Numerical analyses of validation exercises (where there is an analytical solution), as well as of existing triaxial and centrifuge heating tests on Kaolin clay, were carried out in the current paper. The obtained numerical results exhibited good agreement with the analytical solution and experimental measurements respectively, demonstrating good capabilities of the applied numerical facilities and providing insight into the mechanism behind the observed evolution of the thermally induced pore fluid pressure. The numerical results further highlighted the importance of accounting for the temperature-dependent nature of the soil permeability and the thermal expansion coefficient of the pore fluid, commonly ignored in geotechnical numerical analysis.
Cui W, Potts DM, Zdravković L, et al., 2019, Formulation and application of 3D THM-coupled zero-thickness interface elements, Computers and Geotechnics, Vol: 116, Pages: 1-11, ISSN: 0266-352X
Interface elements are frequently employed in finite element (FE) analyses to represent soil-structure interfaces or rock joints. The modelling of coupled thermo-hydro-mechanical (THM) problems in geotechnical engineering requires equally a coupled and robust THM formulation for interface elements. This paper presents such a formulation which is capable of reproducing the coupled THM behaviour of discontinuities and soil-structure boundaries, and is compatible with other types of finite elements used to discretise the soil and structural domains (e.g. solid and shell elements). The coupled THM three-dimensional (3D) zero-thickness interface element is implemented into the bespoke FE code employed in this research and its features are verified using a number of numerical exercises. To demonstrate their performance, the proposed interface elements are employed in the simulation of the coupled THM behaviour of a fissured triaxial sample subjected to a thermal load and the influence of the presence of fissures on soil behaviour is presented.
Ghiadistri G, Zdravković L, Potts DM, et al., 2019, Calibration of a double structure constitutive model for unsaturated compacted soils, 7th International Symposium on Deformation Characteristics of Geomaterials (IS-Glasgow 2019), Publisher: EDP Sciences, Pages: 1-6
This paper describes a calibration procedure for the double structure constitutive model ICDSM (Imperial College Double Structure Model), developed for highly expansive clays, when the model is applied to MX-80 bentonite. Firstly, the model calibration process is discussed and organised in a number of hierarchical steps. These steps involve the estimation of the macrostructural parameters that can be derived from oedometer, isotropic and triaxial laboratory data. Estimation of the microstructural parameters is more challenging due to the limited knowledge of an expansive clay’s fabric and of the physico-chemical phenomena that control its evolution upon wetting. Nevertheless, this paper discusses the available sources of data and identifies the appropriate information that is needed to characterise the micro-structural behaviour of the bentonite. Finally, through the simulation of a swelling pressure test on a bentonite plug, the hydration of the material is studied as a hydro-mechanical coupled process. Particular attention is devoted to the evolution of the stress state of the sample, which is compared to the experimental measurements in order to demonstrate that the constitutive model accurately reproduces the expansive behaviour of MX-80 bentonite.
Ghiadistri GM, Zdravkovic L, Potts DM, et al., 2019, Modelling the behaviour of swelling clays in a Geological Disposal Facility (GDF)
This paper discusses the numerical modelling of the buffer material in a Geological Disposal Facility (GDF), by simulating the FEBEX in-situ experiment. The test was conducted over 18 years at the Grimsel site in Switzerland, under the conditions of a real GDF, with compacted bentonite blocks used as the buffer material and a heater replacing the nuclear waste canister. Particular emphasis in the paper is given to the constitutive modelling of the FEBEX bentonite, highlighting the importance of accounting in the model for the double porosity structure of the compacted bentonite. Furthermore, the coupled thermo-hydro-mechanical (THM) finite element analysis also emphasises the importance of realistic modelling of the evolution of the hydraulic permeability of the bentonite with the changing suctions. The analysis results demonstrate substantial agreement between numerical predictions and FEBEX field measurements in terms of the buffer’s THM evolution. The area of the host formation affected by the test is also defined and investigated in order to provide useful information for the design of a GDF.
Cui W, Potts DM, Zdravkovic L, et al., 2018, A coupled thermo-hydro-mechanical finite element formulation for curved beams in two-dimensions, Computers and Geotechnics, Vol: 103, Pages: 103-114, ISSN: 0266-352X
To enable the use of beam elements in the modelling of coupled thermo-hydro-mechanical (THM) geotechnical problems, a fully coupled and robust THM formulation is required. This paper presents such a formulation which allows both fluid flow and heat transfer along a 2D curved beam, while ensuring compatibility with coupled THM solid elements commonly used to discretise soils. Verification exercises and application with the proposed coupled beam element are carried out to demonstrate its satisfactory behaviour. The results of these analyses are compared against closed form solutions, solutions obtained using solid elements, and field measurements, showing an excellent agreement.
Mantikos V, Tsiampousi A, Standing JR, 2018, Swelling behaviour of an expansive clay at high suction, 7th International Conference on Unsaturated Soils, Publisher: UNSAT
Deep geological disposal designs for nuclear waste often include an engineered barrier to protect the waste canistersand prevent leakage. The long-term safety of the repository relies on studies of the buffermaterial.Oedometer tests provide values ofdesign parameters fornumerical simulations. Anewly-developed oedometer with automated suction control is presented to assist in the investigation of the coupled hydro-me-chanical-volumetric behaviour of an expansive clay, namely a natural sodium bentonite. The displacement-controlled device was developed to apply suctionover a range of10 MPa to 300 MPausing a divided-flow humidity-generator. The device allows the application of combined stress and suction states, and continuous stress paths of constant volume, stress or suction. The development of the new oedometer is described. Results obtained during the preliminary tests are evaluated through comparison with experimental data from similar tests found in the literature. The current method benefits from continuous control of suction with servo-control of relative humidity using calibrated capacitance hygrometers. The system self-compensates for minor temper-ature changes and therefore the requirement for thermal insulation is not as crucial as in vapour equilibrium methods.
Ghiadistri GM, Potts DM, Zdravkovic L, et al., 2018, A new double structure model for expansive clays, 7th International Conference on Unsaturated Soils
The behaviourof compacted bentonite upon hydration is numerically investigated here by simu-lating a swelling pressure teston aMX-80 bentonitesample. Two constitutive modelsareemployed in the analysis: the “Imperial College Single-Structure Model” (ICSSM)andthe “Imperial College Double-Structure Model” (ICDSM), the latterspecifically developed for expansive clays. It is shown that the latter exhibits a considerably improved performance as it is able to accurately capture the swelling pressure developed in the materialupon wetting. Nevertheless, a limited knowledge of the evolution of the material’s fabric, notably at the micro-scale,is an obstacle for deriving with certainty some of the model parameters. This issue is high-lightedhere by performing analyses of theswelling pressure test with two sets ofmaterial characterisations, with model parameters differinginthe derivation of the microstructural component.Both analyses show a very good match with the testdata, but it is difficult to justify one set of microstructural parametersoverthe other. The paper emphasises what aspects of experimental research could be helpful in studying the fabric of compacted bentonite upon wetting, and hence improve the calibration procedure of thedouble-structure mod-el.
Kirkham AD, Tsiampousi A, Potts DM, 2018, Temperature-controlled oedometer testing on compacted bentonite, 7th International Conference on Unsaturated Soils
A new temperature-controlled oedometer has been designed at Imperial College London and commissioned to investigate the thermo-hydro-mechanicalbehaviour of soils. Temperature control is achieved by submerging the specimenin a water bath. The water temperature is regulated byheaters positionedradially around the specimen, or by an external unit. The temperature can be varied between 5°C and 85°C. The temperature gradient across the specimenis minimised by circulating water beneath the specimenthrough a hollow plate.A thermo-mechanical, elastic, finite element model of the equipment has been produced using the Imperial College Finite Element Program (ICFEP). The experimental results are used to develop and validate the numerical model. The model is then used to inform and improve the experimental testing programme.The accuracy of temperature control has already been established. The testing programme includes heating tests at constant applied stress, and loading tests at discrete temperature values. Of particular interest is thermally-inducedoverconsolidation behaviour. The experimental results are used to verify the existing numerical framework and to establish the effect of temperature on the behaviourofsaturated soil.
Zdravkovic L, Tsiampousi A, Potts DM, 2018, On the modelling of soil-atmosphere interaction in cut and natural slopes, 7th International Conference on Unsaturated Soils
The need to predict the consequences of atmospheric conditions on the stability of slopes is widely evident from numerous examples of slope failures around the world, which often result in material and human loss.Equally, the serviceability conditions of cut slopes very much depend onthe heave mobilised byexcavation, the magnitude of which is partly governed by the hydraulic boundary conditions.Soil-atmosphere interaction is complex, involving precipitation and evapotranspiration across the slope surface, and acts in ad-dition to theground water regime within the slope body. As a consequence, calculation tools cannot be overly simplified if realistic predictions are expected. This paper provides an overview of recent research at Imperial College in modellingunsaturatednatural and cut slopes, using finite element analysis and advanced constitutive models and boundary conditions.
Cui W, Tsiampousi A, Potts DM, et al., 2018, Finite element modelling of excess pore fluid pressure around a heat source buried in saturated soils, London, 9th European Conference on Numerical Methods in Geotechnical Engineering, Publisher: Taylor Francis Group, Pages: 741-749
Tsiampousi A, Yu JBY, Standing JR, et al., 2017, Behaviour of bolted cast iron joints, Tunnelling and Underground Space Technology, Vol: 68, Pages: 113-129, ISSN: 0886-7798
The structural testing and finite element (FE) analysis described in this paper were part of a major research project undertaken at Imperial College London to investigate the deformation of bolted segmental grey cast iron (GCI) tunnel linings. A key aim was to quantify how joints influence the behaviour of the lining, through a three-path approach comprising physical experiments, finite element modelling, and field instrumentation. The laboratory results have been used to assess the validity of the tunnel assessment methods used by industry.This study examined joint articulation under the serviceability limit state in the absence of hoop force focussing on factors such as applied bolt preload, the loading direction and the freedom of the circumferential flange to deflect. Two half-scale GCI lining segments were bolted together at the longitudinal flanges to form a bolted arch in a similar fashion to the tests performed by Thomas (1977). Modern instrumentation was implemented to gain detailed measurements quantifying changes in global displacements of the two segments, bolt forces and joint opening under applied loading. For the first time, the physical experiments were conducted contemporaneously with the development of a three-dimensional FE model of the joint. The experimental data and the results from the FE analysis indicate a reduction in joint stiffness as the joint articulates under applied load. It is shown that the presence of a joint has far greater influence on the behaviour of the ‘arch’ than the level of preload applied to the bolts in the joint. The FE analysis allowed the deformation behaviour of the joint under positive and negative bending to be investigated: its response under the two modes differs significantly.
Tsiampousi A, Smith PGC, Potts DM, 2017, Coupled consolidation in unsaturated soils: from a conceptual model to applications in boundary value problems, Computers and Geotechnics, Vol: 84, Pages: 256-277, ISSN: 0266-352X
The paper presents the Finite Element formulation of the equations proposed by Tsiampousi et al. (2016) for coupled consolidation in unsaturated soils. Their coupling is discussed in relation to a conceptual model which divides soil behaviour into zones ranging from fully saturated to dry states. The numerical simulation of a laboratory experiment involving drainage of water from a vertical column of sand is used to validate the equations. Finally, the example of rainfall infiltration into a cut slope highlights how aspects of the conceptual model are reflected in the numerical analysis of boundary value problems involving unsaturated soils.
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