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1
Kite, Matthew J. S. "Computational modelling of clay pipe extrusion." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources. Online version available for University members only until June 9, 2014, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=25966.
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Evans, D. G. "Modelling a china clay band dryer." Thesis, University of Exeter, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383097.
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De, Moor E. K. "Modelling of deep tunnel behaviour in clay." Thesis, City University London, 1989. http://openaccess.city.ac.uk/7396/.
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Several aspects of the ground response to tunnel excavation in deep clay formations have been studied. Such strata may be only lightly overconsolidated and an unsupported tunnel could have a high stability ratio. Consequently, at large depths there may be construcz ion difficulties similar to those encountered in soft ground at shallow depths. Problems which may be encountered are squeezing ground, i.e. a continually increasing volume loss with time, and possible collapse after a 'stand-up' time. A range of parameters likely to influence the time dependent deformation behaviour at an unsupported tunnel face was investigated in a number of small scale model tunnel tests. The tests were performed in large cylindrical samples of kaolin clay under axisymmetric conditions, with measurement of tunnel face displacement and pore pressure changes in the clay. After removal of the tunnel face support, soil intruded into the tunnel at a rate which gradually increased with time until a constant rate was reached. The steadily increasing deformation was frequently associated with increasing pore pressures close to the tunnel face as water flow occurred towards the tunnel face due to the changed boundary conditions. Two parameters, the initial pore pressure in the soil and the initial load factor, were shown to have a major influence on the time dependent behaviour, and were incorporated into a new deformation time factor. Initial undrained pore pressure changes caused by the removal of tunnel face support have been compared with simplified closed form solutions for the thick cylinder and thick sphere analogue. As a result two zones were identified at the tunnel face, in which either approximately cylindrical or spherical behaviour was observed. The small scale tests were modelled numerically using the finite element program CRISP. Elasto-plastic soil behaviour and consolidation were included in the analyses. Although the predictions were affected by the complex geometry and boundary conditions of the model tests, the mechanics of the time dependent deformations were demonstrated. Deformations at the tunnel face were poorly predicted and pore pressure changes were confined to smaller zones than in the model tests. However, comparisons of the finite element predictions and the closed form solutions for the plastic zone were more favourable. Longe term pore pressure predictions showed only limited agreement with the experimental behaviour. For both the model tunnel and thick cylinder, CRISP predicted localized zones of softened soil close to the unsupported boundary which developed over a very short time period. The rapid local drainage implies that time dependent movements will be observed which are governed by changes in pore pressure and water flow.
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Ellison, Kirk Carr. "Constitutive modelling of a heavily overconsolidated clay." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610606.
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Wang, Yan. "Exploring Biopolymer-Clay Nanocomposite Materials by Molecular Modelling." Doctoral thesis, KTH, Teoretisk kemi och biologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-166299.
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In this thesis, bio-nanocomposites made from two alternative biopolymers and montmorillonite (Mnt) clay have been investigated by molecular modelling. These biopolymers are xyloglucan (XG) and chitosan (CHS), both of which are abundant, renewable, and cost-effective. After being reinforced by Mnt clay nanoparticles, the polymer nanocomposites gains in multifunctionality and in the possibility to register unique combinations of properties, like mechanical, biodegradable, electrical, thermal and gas barrier properties. I apply molecular dynamics (MD) simulations to study the interfacial mechanisms of the adhesion of these biopolymers to the Mnt nanoplatelets at an atomic level. For the XG-Mnt system, a strong binding affinity of XG to a fully hydrated Mnt interface was demonstrated. It was concluded that the dominant driving force for the interfacing is the enthalpy, i.e. the potential energy of the XG-Mnt interacting system. The adsorbed XG favors a flat conformation with a galactose residue in its side chain that facilitates the adsorption of the polymer to the nanoclay. The XG adsorption was found do depend strongly on the hydration ability of counterions. The binding affinity of XG to Mnt was found to be strongest in the K-Mnt/XG system, followed by, in decreasing order, Na-Mnt/XG, Li-Mnt/XG, and Ca-Mnt/XG. The competing mechanism between ions, water and the XG in the interlayer region was shown to play an important role. The dimensional stability upon moisture exposure, i.e. the ability of a material to resist swelling, is an important parameter for biopolymer-clay nanocomposites. While pure clay swells significantly even at low hydration levels, it is here shown that for the XG-Mnt system, at a hydration level below 50%, the inter-lamellar spacing is well preserved, suggesting a stable material performance. However, at higher hydration levels, the XG-Mnt composite was found to exhibit swelling at the same rate as the pure hydrated Mnt clay. For the CHS-Mnt system, the significant electrostatic interactions from the direct charge-charge attraction between the polymer and the Mnt clay play a key role in the composite formation. Varying the degree of acetylation (DA) and the degree of protonation (DPr) resulted in different effects on the polymer-clay interaction. For the heavily acetylated CHS (DA > 50%, also known as chitin), the strong adhesion of the neutral chitin to the Mnt clay was attributed to strong correlation between the acetyl functional groups and the counterions which act as an electrostatic “glue”. Similarly, the poor adhesion of the fully deprotonated (DPr = 0%) neutral CHS to the clay is attributed to a weak correlation between the amino functional group and the counterions. The stress-strain behavior of the CHS-Mnt composite shows that the mechanical properties are highly affected by the volume fraction of the Mnt clay and the degree of exfoliation of the composite. The material structure has a close relationship to the material properties. Biopolymer-clay nanocomposites hold a bright future to replace petroleum-derived polymer plastics and will become widely used in common life. The theme of the thesis is that further critical improvements of these materials can be accomplished by development of the experimental methods in conjunction with increased understanding of the interactions between polymer, clay, water, ions, solutions in the polymer-clay mixtures provided by molecular modelling.I denna avhandling har molekylär modellering och molekyldynamisk (MD) simulering använts för att studera modellsystem för bio-nanokompositer bestående av montmorillonit-lera samt två olika sorters biopolymerer – xyloglukan (XG) och kitosan (CHS). Båda dessa polymerer är naturligt förekommande och mycket vanliga. De är dessutom förnyelsebara och kostnadseffektiva. Då polymererna förstärkts med nanopartiklar av montmorillonit får det resulterande kompositmaterialet en unik kombination av egenskaper såsom mekaniska, elektriska, termiska och barriär egenskaper etc. Genom att använda molekyldynamiska (MD) simuleringar, studeras här växelverkan mellan dessa biopolymerer och lernanopartiklar (Mnt) på grundläggande atomistisk detaljnivå. Mellan XG och Mnt i ett fullt hydrerat system kunde stark bindningsaffinitet påvisas. Den dominerande drivkraften för affiniteten var entalpi, d.v.s. potentiell växelverkansenergi. Den adsorberade XG-kedjan antar en platt konformation på ytan. Ett förslag utifrån simuleringsresultaten var att galaktosresidyn i xyloglukanets sidokedja underlättar adsorptionen till lerytan. Simuleringarna kunde också visa att adsorption av XG till Mnt beror starkt på motjonernas hydreringsförmåga. Bindningsaffiniteten mellan XG och Mnt var som starkast i K-Mnt/XG- systemet. Därefter följde, i minskande ordning, Na-Mnt/XG, Li-Mnt/XG och Ca-Mnt/XG. Det kunde visas att strukturen vid gränsytan styrs av konkurrerande mekanismer mellan joner, vatten och XG. Dimensionsstabilitet vid fuktexponering, d.v.s. förmågan hos ett material att motverka svällning, är en viktig egenskap för biopolymer-lernanokompositer. Ren lera sväller signifikant även vid låga fukthalter. Dock kunde MD simuleringar visa att ett modellsystem av XG-Mnt behåller sitt ursprungliga interlamellära avstånd vid hydreringsnivåer under 50%, vilket indikerar ett stabilare material. Vid högre hydrering uppmättes dock svällningen vara densamma som för ren lera. I CHS-Mnt-systemet visade det sig att direkt elektrostatisk växelverkan med signifikant styrka mellan laddningar på polymer och Mnt-yta spelar störst roll för kompositformeringen. Olika effekt på polymer-lerväxelverkan uppnåddes genom att variera acetyleringsgraden (DA) respektive protoneringsgraden (DPr). För den tungt acetylerade CHS-polymeren (DA > 50%, även kallad kitin) visade sig den starka vidhäftningen bero på korrelation mellan acetylgrupperna och motjonerna som i sin tur verkade som ett elektrostatiskt “lim”. På liknande sätt kunde den svaga vidhäftningen mellan fullt deprotonerad (DPr = 0%) neutral CHS och lera förklaras med en betydligt svagare korrelation mellan aminogrupperna och motjonerna. Spänning-töjningsbeteendet hos CHS-Mnt modellen visar att dess mekaniska egenskaper beror kraftigt på volymsandelen Mnt och graden av exfoliering i kompositen. Materialets struktur är nära relaterat till materialegenskaperna. Framtiden för nanokompositer av biopolymerer och lera är ljus då de kan komma att ersätta oljebaserade plaster och användas frekvent i våra dagliga liv. Materialen kommer successivt förbättras genom utveckling av experimentella metoder i kombination med molekylmodellering för ökad förståelse för växelverkan mellan polymer, lera, vatten, joner och lösningsmedel.
本论文利用分子动力学模拟技术研究了两种备选生物大分子与蒙脱土(Montmorillonite, Mnt)（一种粘土）组成的生物纳米复合材料，分别是木葡聚糖（Xyloglucan, XG）/蒙脱土和壳聚糖(Chitosan, CHS)/蒙脱土。木葡聚糖与壳聚糖都是自然界广泛存在的生物大分子，资源丰富且取材面宽，提取及加工成本低廉，加之可以生物降解并可再生，是优秀的生物复合材料备选原料。经过蒙脱土纳米颗粒加固后，这些基于生物大分子的复合材料将获得多功能且有多种独特特性相结合的优点，比如，更好的力学性能，生物可降解，良好的导电性能，传热性能和屏蔽气体与液体侵扰的能力等等。论文中，我们采用分子动力学模拟的方法着重对生物大分子与蒙脱土在界面上的粘附相互作用机理进行了深入探讨。 首先，对于木葡聚糖/蒙脱土纳米复合材料，我们发现糖分子与土分子间有着很强的天然亲和力。研究证明它们之间的这种相互作用，热焓是主要的推动力，也就是糖和土分子间的相互作用势能。含有半乳糖残基的木葡聚糖分子（本文中亦称天然木葡聚糖分子）吸附到粘土表面后，分子构型呈现扁平状，半乳糖残基似有辅助木葡聚糖大分子吸附到粘土颗粒上的作用。 进一步研究发现，木葡聚糖分子在粘土表面上的吸附与溶液中抗衡离子的水和作用密切相关。在钾离子平衡的糖/粘土系统中，糖分子与土分子的相互作用最强，钠离子平衡的糖/粘土系统次之，紧接着是锂离子平衡的糖/粘土系统，最弱的是钙离子平衡的糖/粘土系统。研究发现，离子，水分子，以及糖分子在粘土层间的竞争机制在糖分子的粘附过程中起着重要的作用。 材料暴露于潮湿环境中的尺寸稳定性，也就是材料抗肿胀的能力是生物大分子/蒙脱土所构成的复合材料的重要参数。蒙脱土自身即使在很低的潮湿环境下就会有明显地膨胀现象，然而，对木葡聚糖/蒙脱土复合材料来说，尺寸稳定性可以在水和值低于50%以下有效保存。其夹层尺寸的稳定保持暗示了材料在这个程度的潮湿环境下的稳定性。然而，当水和值高于50%时，木葡聚糖/蒙脱土复合材料将出现明显的肿胀现象，表现在夹层尺寸的明显增大，且其膨胀速率与粘土自身的膨胀速率逐渐趋于相当水平。 其次，对于壳聚糖/蒙脱土复合材料，我们发现由电荷-电荷间直接产生地强烈的静电吸引作用是壳聚糖分子与蒙脱土分子相互粘附并构成复合材料的关键因素。通过改变壳聚糖分子的乙酰化程度（Degree of acetylation, DA）和质子化程度(Degree of protonation, DPr)，糖分子与土分子的相互作用有着显著地不同。对于乙酰化程度（DA）高于50%的壳聚糖分子（亦成为甲壳素分子chitin, CHT），电中性的甲壳素分子与土分子间的强吸附作用源于乙酰基功能团与抗衡离子的强相关性。抗衡离子此时扮演着类似于“电子胶”的作用，可以有效地将电中性的甲壳素分子与土分子粘结在一起。类似地，当质子化程度最低时，亦即壳聚糖分子完全非质子化，即呈现电中性时，较差的糖/土吸附作用源于氨基功能团与抗衡离子的较弱的相关性。 进一步对壳聚糖/蒙脱土复合材料的分子系统进行应力应变计算发现，复合材料的力学性能直接受蒙脱土体积分数和其剥离程度的影响，通常，粘土的体积分数越大体系的力学性能越高，且剥离程度对材料的整体性能也有直接影响。因此，材料的结构与其性能的表征有着密切联系。 我们相信生物大分子与蒙脱土构成的生物复合材料有着光明的前景，可以取代石油提取物制成的塑料材料，并将能够广泛应用在日常生活中。通过实验技术的改善和应用分子模拟技术对复合材料体系中生物大分子，蒙脱土分子，水分子，离子，溶液环境等混合物质相互作用的理解增加，这种可再生的新材料将会得到重要改进，这也是整本论文的主旋律。
QC 20150520
Bio-nanocomposites
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Grace, Tim, and n/a. "An investigation of primary school children's clay modelling techniques." University of Canberra. Education, 1993. http://erl.canberra.edu.au./public/adt-AUC20060712.130505.
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Children in their final years of primary schooling tend to emphasize the
use of detail and the production of naturalistic representations, when
modelling the human figure with clay. Children of this age rarely
construct clay figures which are noted for their dynamic quality in terms
of finish, proportion, or pose.
This study examined the effect of using a "formative" modelling
technique on the clay models made by 11 year old children. Involved
in the study were two groups of 11 year old children. Both groups of
children undertook a pre-test, a post-test, and a series of clay
modelling activities similar to other activities described in most primary
school art curricula. The experimental group of children were
instructed in the use of a "formative" modelling technique in which
children develop their clay figures from a single mass of clay and
refrain from constructing the figures by a combination of separate
parts. The control group received no instruction.
Brown's Modified "Secondary" Characteristics Rating Scale was used
to identify differences between pre- and post-test clay figures.
Results suggest that the "formative" modelling technique did not induce
a different approach to the modelling of finish, proportion, and pose in
the clay figures made by boys and girls 11 years of age. However,
there was evidence of a gender difference.
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Morris, Jonathan David. "Physical and numerical modelling of grouted nails in clay." Thesis, University of Oxford, 1999. http://ora.ox.ac.uk/objects/uuid:530eeb78-5ead-4459-8733-3e6ae722c687.
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The research described in this thesis focussed on the bond resistance of grouted soil nails in clay. Physical modelling took the form of large scale element tests in the laboratory of drilled and grouted nails in a stiff clay. Nails were installed under different boundary stresses; testing was conducted at different constant rates of pull-out and also under sustained load conditions. Observed behaviour was compared with that predicted by measurements of interface shear resistance obtained in a conventional shear box. Numerical modelling was carried out in an attempt to improve understanding of the effects of installation processes on nail performance, and to investigate the trends in behaviour observed during laboratory tests. For this purpose, a one-dimensional finite element computer program was developed to include the effects of consolidation and the out-of-plane soil displacements associated with nail axial loading. The physical modelling showed that the loading rate has a significant effect on bond resistance. This has consequences for the interpretation of data from constant rate of displacement pull-out testing, the conventional method of verifying bond resistance in the field. It is suggested that this type of testing is inappropriate in low permeability soils, because capillary suctions develop which lead to increased bond resistance. Results from laboratory sustained load tests show that lower values of bond resistance are mobilised under the static load conditions more likely to exist in a real soil nailed structure. The numerical modelling confirms the behaviour observed during the laboratory tests, and shows that the mechanisms by which bond is mobilised are complex, depending critically on the dilation and consolidation characteristics of the soil. Nail installation procedures are modelled, and grout pressures are shown to strongly influence bond resistance. Interface tests show trends in behaviour similar to those observed during pull-out testing. However, difficulties exist in the qualitative use of interface test data to predict nail bond resistance.
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Nigussie, Daniel Gebremedhin. "Numerical modelling of run-out of sensitive clay slide debris." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bygg, anlegg og transport, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23329.
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Flow slides in sensitive clay deposits are common phenomena in Scandinavia and Canada. These flow slides have caused catastrophes to infrastructure and human life. The post-failure movements of such flow slides usually are characterized by their retrogression distances and or by the run-out distance of the slide debris. There are empirical and numerical methods used to assess the retrogression distance of slide debris. On contrary, convincing and accurate modeling techniques for run-out of sensitive clay slide debris, which is a very complex and challenging process, is yet to be developed Keeping this in view, this work presents a preliminary study to understand the run-out process in sensitive clay slide debris. An available numerical tool called DAN3D has been used to simulate the run-out process of three large flow slides occurred in Norway. In addition, back-calculation of a laboratory scale model test has been performed. A standardized calibration and adjustments on the models based on back analysis of real cases has to be done to use such models on sensitive clay debris analysis extensively. The Study shows that a very simple plastic model in DAN3D is able to estimate the run-out distance and the process.
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Mrayed, Sabri Mohamed Ali Chemical Sciences & Engineering Faculty of Engineering UNSW. "Molecular modelling applications in crystallization fouling and clay/polymer nanocomposites." Awarded by:University of New South Wales. Chemical Sciences & Engineering, 2007. http://handle.unsw.edu.au/1959.4/40682.
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The present work used ab initio density functional theory (DFT) to study two different physical phenomena crystallization fouling and clay-based polymer nanocomposites. In the first part, two foulant materials were studied including calcium carbonate, and calcium sulfate. The lattice energy and enthalpy of formations of each crystal system were predicted using DFT methods. The most stable forms of calcium carbonate foul ant, calcite and aragonite, were investigated. For calcium sulfate, both gypsum and anhydrite crystals were investigated. The thermodynamic solubility product of each crystal system, for both foul ants, was predicted from the lattice energy and enthalpy of formations. Comparison of the stability between the different crystal systems for the same foul ant material was carried out to elucidate the effect of crystal atomic configuration and space group on the stability of foulant materials. The effect of temperature on the formation and stability of foulant material was also carried out. The results obtained using DFT methods, for enthalpy of formation and thermodynamic solubility products, were comparable with the experimental data reported in the literature. In the second part, study has been made on the clay-based nylon 6 nanocomposite materials. The purpose was to understand the interfacial interactions between clay and polymer with and without surfactant component. Both sides of the clay were examined with nylon 6. In order to determine specifically the type of interfacial interaction between clay and nylon 6, the electron distribution around the whole system was predicted. The study was carried out at various isomorphic substitutions. The substitutions took place at both octahedral and tetrahedral layers of the clay. The strength between clay and nylon 6 was predicted by calculating the binding energy. The results obtained revealed that, the strength increases with the increase in the degree of isomorphic substitutions. The type of bond between nylon 6 and basal surface of the clay was found to be basically electrostatic interactions, and particularly hydrogen bonds. Whilst, the type of interactions between nylon 6 and clay edge surface was found to include covalent bonds as well as electrostatic interactions. The formation and breakage of covalent bonds between nylon 6 and clay means that, a chemical decomposition of the clay can happen when it is mixed with certain type of polymers. The presence of surfactant can decrease the interfacial interactions between clay and nylon 6.
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Lee, Yat Sun. "Physical and numerical modelling of pipe-soil interaction in clay." Thesis, University of Sheffield, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.577564.
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To relieve the axial stress induce rature high-pressure pipelines in deepwater, current design methods leave the pipe unburied and allow the formation of the lateral buckles along the pipeline in a controlled manner. However, this approach requires a better understanding of the interaction between the seabed soil and the partially embedded pipeline under both vertical and lateral movements. Research has been carried out to examine the two soil-pipe interaction mechanisms, vertical pipe penetration and lateral pipe movement, involved in the installation and operation of an on-bottom offshore pipeline. The findings reported in this thesis improve the current knowledge of pipe-soil interaction in clay. A series of physical model tests was conducted to investigate the behaviour of pipe penetration and lateral pipe movement in clay. The experiments were carried out using short pipe sections in a I g model tank equipped with a transparent Perspex window in the front panel, from which high quality images were obtained for the measurement of the soil deformation in the tests using an image analysis technique. The computational limit analysis, Discontinuity Layout Optimisation (DLO), was adopted to back-analyse and compare with the experimental results. In addition, parametric studies were conducted using DLO to investigate the effects of the change in soil geometry and soil condition on the pipe resistances and soil flow mechanisms for the vertical pipe penetration and the lateral pipe sweep processes. Experimental results showed that pipe penetration, prior to the fully embedded flow-around failure mechanism at very deep penetrations, involves four distinct stages in development of the failure mechanism from 'soil heave' to 'local flow-around' at shallow and deep pipe embedments, respectively. Good agreement was observed between the experimental and numerical results. The results of the parametric studies suggested that the onset depth of the fully embedded flow-around failure mechanism is strongly dependent on the undrained strength profile and tensile strength of the soil. The lateral resistance of a partially embedded pipe under different loading conditions was measured at both small and large lateral displacements. Results showed that the lateral resistance is strongly affected by the change in soil geometry, soil heave induced by the initial penetration and formation of the active berm in front of the pipe during lateral movements. Based on the results from the numerical and experimental studies, design equations are proposed for the predictions of (i) the pipe penetration resistance at both shallow and deep embedments, and (ii) the lateral resistance of a partially embedded pipe under combined vertical and horizontal loads at both small and large lateral displacements.
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Gonzalez‐Blanco, Laura. "Gas migration in deep argillaceous formations : Boom clay and indurated clays." Doctoral thesis, Universitat Politècnica de Catalunya, 2017. http://hdl.handle.net/10803/406355.
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Deep geological disposal remains the preferred option at present for the management of long-living and heat-emitting radioactive waste, which consists of confining the waste during a very long period (several hundreds of thousands of years) by placing them in a deep geological formation. Therefore, the understanding of the long-term behaviour of formations is becoming a key issue to ensure the feasibility of the geological disposal
facilities, particularly regarding the generation and migration of gases. The present PhD work aims at better understanding the complex hydro-mechanical response of different argillaceous formations to gas migration process. To this end, gas flow through Boom Clay (one of the potential candidate plastic Paleogene clay formations to host nuclear waste in Belgium) has been deeply investigated on the basis of laboratory experiments at different scales and their numerical modelling. This main study has been complemented by presenting tests on two indurated and deeper claystone Mesozoicformations, considered as candidate host rocks in the Swiss programme for deep geological disposal, namely Opalinus Clay and ‘Brauner Dogger’.
The different materials have been firstly characterised to evaluate mechanical (compressibility on loading) and two phase flow properties (water retention and permeability). Gas injection tests under oedometer and isotropic conditions have been performed following different testing protocols, in which boundary conditions have been carefully controlled. Major relevance has been given to restore the in situ stress state
and to ensure full saturation conditions before the gas tests. Special emphasis has been placed in measuring sample deformation along the gas injection and dissipation process. The anisotropy of Boom Clay has been studied by carrying out tests with bedding planes parallel and normal to flow. Air injections have been performed at three different controlled-volume rates. The dissipation stages after shut-off have been also analysed to study air intrinsic permeability changes. Microstructure of samples before and after air injection tests has been evaluated by different techniques: mercury intrusion porosimetry, field-emission scanning electron microscopy and micro-focus Xray computed tomography.
Gas migration turned out to be a fully coupled hydro-mechanical process. Air injection at constant stress induced expansion of the samples during pressure front propagation and compression during air pressure dissipation. The deformational behaviour was dependent on the injection rate. At slower injection rates expansion occurred during the injection while at higher rates it was delayed in time. Air intrinsic permeability resulted higher than water permeability suggesting that air flow took place along preferential pathways. Evaluation of the microstructural changes induced by air migration revealed the opening of fissures and allowed quantifying their apertures and separation, as well as their volume and connectivity. Air intrinsic permeability was found to be dependent on the fissured volume.
To complete and better understand the gas transport mechanisms, numerical simulations of the experimental results have been performed using a fully coupled hydro-mechanical finite element code, which incorporates an embedded fracture permeability model to account for the correct simulation of the gas flow along preferential pathways. Clay intrinsic permeability and its retention curve have been made depend on strains through fracture aperture changes. Numerical results not only accounted for the correct simulation of the recorded upstream pressures and outflow
volumes and pressures, but also for the volume change behaviour. The experimental and numerical information provided a good insight into the mechanisms of gas transport in deep clay formations and highlighted the role played by the deformational response on the air transport properties of argillaceous rock formations.El almacenamiento geológico profundo es la solución actualmente aceptada para la gestión de los residuos radioactivos de alta actividad, que consiste en confinar dichos residuos durante un período muy largo de tiempo (varios cientos de miles de años) depositándolos en una formación geológica profunda. De ahí que el entendimiento del comportamiento a largo plazo se esté convirtiendo en una cuestión clave para asegurar la viabilidad de las instalaciones de almacenamiento de residuos, particularmente en lo que respecta a la generación y migración de gases. Este trabajo de doctorado tiene como objetivo mejorar la comprensión en lo que se refiere a la compleja respuesta hidro-mecánica de diferentes formaciones arcillosas frente a procesos de migración de gas. Con este objetivo, el flujo de gas a través de la arcilla Boom Clay (arcilla plástica del paleógeno candidata a alojar los residuos nucleares en Bélgica) se ha investigado en profundidad mediante experimentos de laboratorio a diferentes escalas y su modelación numérica. Este estudio principal se ha complementado con ensayos experimentales en dos formaciones arcillosas del mesozoico (más profundas y endurecidas),posibles candidatas a roca huésped en el programa suizo para el almacenamiento geológico profundo, llamadas Opalinus Clay y 'Brauner Dogger'. Inicialmente, los diferentes materiales han sido caracterizados para evaluar sus propiedades mecánicas (compresibilidad en carga) e hidráulicas (retención de agua y permeabilidad). Los ensayos de inyección de gas, bajo condiciones edométricas e isótropas, se han realizado siguiendo diferentes protocolos de ensayo controlando cuidadosamente las condiciones de contorno, así como, dando prioridad al hecho de restaurar el estado tensional in situ y las condiciones de saturación antes de los ensayos de gas. Además, se ha hecho especial hincapié en la medición de la deformación de las muestras a lo largo de los procesos de inyección y disipación de gas. La anisotropía de la Boom Clay se ha tenido en cuenta realizando ensayos con los planos de estratificación dispuestos en paralelo y perpendicular al flujo. Las inyecciones de aire se han realizado a tres velocidades volumétricas diferentes. Las etapas de disipación se han analizado para evaluar los cambios en la permeabilidad intrínseca al aire. La microestructura de las muestras se ha evaluado antes y después de los ensayos de inyección de aire mediante tres técnicas diferentes: porosimetría de intrusión de mercurio, microscopía electrónica de barrido de emisión de campo y micro-tomografía computarizada La migración de gases en estas rocas arcillosas saturadas resultó ser un proceso hidro-mecánico totalmente acoplado. La inyección de aire a tensión constante produjo expansión de las muestras durante la propagación del frente de presión y compresión durante la disipación de la presión de aire. El comportamiento deformacional dependió de la velocidad de inyección. A velocidades de inyección más lentas, la expansión se produjo durante la inyección, mientras que, a velocidades más altas, ésta se retrasó en el tiempo. La permeabilidad intrínseca al aire resultó ser más alta que la permeabilidad al agua medida, lo que sugiere que el flujo de aire tuvo lugar a lo largo de vías preferenciales. La evaluación de los cambios microestructurales inducidos por la migración de aire reveló la apertura de fisuras, cuantificando sus aperturas y separación, así como su volumen y conectividad, lo que permitió encontrar una relación de dependencia entre la permeabilidad intrínseca al aire y el volumen fisurado. Para completar la información experimental y comprender mejor los mecanismos de transporte de gas, se realizaron simulaciones numéricas de los resultados experimentales utilizando un código de elementos finitos acoplado, que incorpora un modelo de permeabilidad con fracturas embebidas para explicar el flujo de gas a lo largo de vías preferenciales. La permeabilidad intrínseca de la arcilla y su curva de retención dependen de la deformación a través de cambios en la apertura de la fractura. Los resultados numéricos no sólo reprodujeron de forma correcta las presiones registradas y los volúmenes de salida, sino también el comportamiento deformacional. Esta información experimental y numérica proporcionó una buena visión de los mecanismos de transporte de gas en formaciones arcillosas profundas y en los que destacó el papel desempeñado por la respuesta deformacional sobre las propiedades de transporte de aire.
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Dasari, Ganeswara Rao. "Modelling the variation of soil stiffness during sequential construction." Thesis, University of Cambridge, 1996. https://www.repository.cam.ac.uk/handle/1810/272773.
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Malikiossis, Ariane A. A. "Experiences through clay, therapeutic modelling and ceramics in two anthroposophic communities." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ43628.pdf.
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Sandström, Malin. "Numerical Modelling and Sensitivity Analysis of Tunnel Deformations in London Clay." Thesis, KTH, Jord- och bergmekanik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-191257.
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In dense cities, the interactions between all structures, from tall skyscrapers to complex underground tunnel systems, need to be carefully analysed as soon as a new project is considered. This is necessary because of the stress changes in the soil induced by each new construction. Demolishing a building could cause heave at the base of the excavation, deflections in supporting structures and settlements of the surroundings. The behaviour can be modelled in order to predict how large the deformations will be. This thesis investigates the effectiveness of such models. This is done through the application of a parameter sensitivity analysis on models created in Plaxis. The purpose of the analysis is to identify which factors cause discrepancies between the models and the actual displacements monitored on site. The project being examined is located in central London. The analysis focuses on the displacements of existing tunnels below the site caused by the demolition of two buildings. An analysis was carried out to investigate the significance of different parameters, of different material models and methods of analysis, of 3D effects and of inaccurate groundwater data. Ground investigations, laboratory tests and published data were the main sources used to collect reliable initial input parameters for the material models. A model was created in Plaxis 2D using the Mohr-Coulomb and the Hardening Soil with small-strain stiffness material models, using two types of undrained analysis. A model using the Mohr-Coulomb material model was created in Plaxis 3D as well. A sensitivity analysis was then carried out on the 2D models to identify which input parameters were most significant to the tunnel displacements. The results were compared to monitoring data and a back-analysis was carried out to produce more accurate results. The initial and adjusted input parameters were also tested on the 3D model. Finally, the groundwater level was altered. The results indicate that soil stiffness and effective cohesion are the most significant. Small-strain stiffness is shown to be especially important when analysing small tunnel deformation. The 3D model generally yielded more accurate results than the 2D model, while the groundwater level did not appear to affect the deformations.I tätbebyggda städer bör samspelet mellan olika konstruktioner, från skyskrapor till tunnelsystem, analyseras noga så fort ett nytt projekt ska påbörjas. Detta är kritiskt på grund av den förändrade spänningsfördelning som uppstår i marken vid varje ny byggnation. Marken häver sig, stödmurar deformeras och den omkringliggande marken sätter sig när en byggnad rivs. Denna process kan modelleras för att uppskatta hur stora deformationerna kommer att bli. Det här examensarbetet utvärderar hur effektiv en sådan modell är. En känslighetsanalys utfördes på modeller skapade i Plaxis. Syftet med denna analys är att undersöka vilka faktorer som orsakar skillnader mellan modellerna och mätdata. Projektet ligger i centrala London och analysen fokuserar på tunneldeformationer orsakade av att två byggnader rivs. Tunnlarna befinner sig i ett lager av Londonlera under byggarbetsplatsen. En analys utfördes för att undersöka huruvida olika parameterar, olika materialmodeller och analysmetoder, 3D effekter och grundvattennivån påverkar tunnelförflyttningarna. Markundersökningar, labbtester och publicerad data användes som grund för att bestämma indatavärden. En 2D modell skapades i Plaxis genom att använda materialmodellerna Mohr-Coulomb och ”Hardening Soil with small-strain stiffness”. En Mohr-Coulomb modell skapades dessutom i Plaxis 3D. En känslighetsanalys utfördes sedan på 2D modellen för att identifiera vilka parametrar som påverkade tunnelförflyttningarna mest. Resultaten jämfördes med mätdata och viktiga parameterar ändrades för att ge bättre resultat. Inverkan av att ändra dessa värden undersöktes även i 3D modellen. Slutligen undersöktes påverkan av en förhöjd grundvattennivå. Resultaten antyder att jordens styvhet och den effektiva kohesionen har störst inverkan på resultaten. Styvheten vid små töjningar visar sig vara särskilt viktigt eftersom deformationerna år små. 3D modellen gav generellt sätt mer korrekta resultat än modellen i 2D. En högre grundvattennivå påverkade inte resultaten nämnvärt.
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Summersgill, Freya. "Numerical modelling of stiff clay cut slopes with nonlocal strain regularisation." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/34567.
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The aim of this project is to investigate the stability of cut slopes in stiff clay. The findings are subsequently applied to model stabilisation with piles, used to remediate failure of existing slopes and stabilise potentially unstable slopes created by widening transport corridors. Stiff clay is a strain softening material, meaning that soil strength reduces as the material is strained, for example in the formation of a slip surface. In an excavated slope this can lead to a progressive, brittle slope failure. Simulation of strain softening behaviour is therefore an important aspect to model. The interaction of piles and stiff clay cut slopes is investigated using the Imperial College Geotechnics section's finite element program ICFEP. In designing a suitable layout of the finite element mesh, preliminary analyses found the two existing local strain softening models to be very dependent on the size and arrangement of elements. To mitigate this shortcoming, a nonlocal strain softening model was implemented in ICFEP. This model controls the development of strain by relating the surrounding strains to the calculation of strain at that point, using a weighting function. Three variations of the nonlocal formulation are evaluated in terms of their mesh dependence. A parametric study with simple shear and biaxial compression analyses evaluated the new parameters required by the nonlocal strain softening model. The nonlocal results demonstrated very low mesh dependence and a clear improvement on the local strain softening models. In order to examine the mesh dependence of the new model in a boundary value problem compared to the local strain softening approach, excavated slope analyses without piles were first performed. The slope was modelled in plane strain with coupled consolidation. These analyses also investigated other factors such as the impact of adopting a small strain stiffness material model on the development of the failure mechanism and the impact of the spatial variation of permeability on the time to failure. The final set of analyses constructed vertical stabilisation piles in the excavated slope, represented as either solid elements or one dimensional beam elements. The development of various failure mechanisms for stiff clay cuttings was found to be dependent on pile location, pile diameter and pile length. This project provides an insight into the constitutive model and boundary conditions required to study stabilisation piles in a stiff clay cutting. The nonlocal model performed very well to reduce mesh dependence, confirming the biaxial compression results. However, the use of coupled consolidation was found to cause further mesh dependence of the results.
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Iskander, K. F. "A new approach in modelling undrained clay behaviour during pressuremeter test." Doctoral thesis, Universite Libre de Bruxelles, 1999. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211850.
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Bachmaf, Samer. "Uranium sorption on clay minerals." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2010. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-62404.
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The objective of the work described in this thesis was to understand sorption reactions of uranium occurring at the water-clay mineral interfaces in the presence and absence of arsenic and other inorganic ligands. Uranium(VI) removal by clay minerals is influenced by a large number of factors including: type of clay mineral, pH, ionic strength, partial pressure of CO2, load of the sorbent, total amount of U present, and the presence of arsenate and other inorganic ligands such as sulfate, carbonate, and phosphate. Both sulfate and carbonate reduced uranium sorption onto IBECO bentonite due to the competition between SO42- or CO32- ions and the uranyl ion for sorption sites, or the formation of uranyl-sulfate or uranyl-carbonate complexes. Phosphate is a successful ligand to promote U(VI) removal from the aqueous solution through formation of ternary surface complexes with a surface site of bentonite.
In terms of the type of clay mineral used, KGa-1b and KGa-2 kaolinites showed much greater uranium sorption than the other clay minerals (STx-1b, SWy-2, and IBECO montmorillonites) due to more aluminol sites available, which have higher affinity toward uranium than silanol sites. Sorption of uranium on montmorillonites showed a distinct dependency on sodium concentrations because of the effective competition between uranyl and sodium ions, whereas less significant differences in sorption were found for kaolinite. A multisite layer surface complexation model was able to account for U uptake on different clay minerals under a wide range of experimental conditions. The model involved eight surface reactions binding to aluminol and silanol edge sites of montmorillonite and to aluminol and titanol surface sites of kaolinite, respectively. The sorption constants were determined from the experimental data by using the parameter estimation code PEST together with PHREEQC. The PEST- PHREEQC approach indicated an extremely powerful tool compared to FITEQL.
In column experiments, U(VI) was also significantly retarded due to adsorptive interaction with the porous media, requiring hundreds of pore volumes to achieve breakthrough. Concerning the U(VI) desorption, columns packed with STx-1b and SWy-2 exhibited irreversible sorption, whereas columns packed with KGa-1b and KGa-2 demonstrated slow, but complete desorption. Furthermore, most phenomena observed in batch experiments were recognized in the column experiments, too.
The affinity of uranium to clay minerals was higher than that of arsenate. In systems containing uranium and arsenate, the period required to achieve the breakthrough in all columns was significantly longer when the solution was adjusted to pH 6, due to the formation of the uranyl-arsenate complex. In contrast, when pH was adjusted to 3, competitive sorption for U(VI) and As(V) accelerated the breakthrough for both elements.
Finally, experiments without sorbing material conducted for higher concentrations of uranium and arsenic showed no loss of total arsenic and uranium in non-filtered samples. In contrast, significant loss was observed after filtration probably indicating the precipitation of a U/As 1:1 phase.
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Mwamila, Luhuvilo. "Arsenic (V) and Phosphate sorption to Swedish clay soils - Freundlich sorption modelling." Thesis, KTH, Miljögeokemi och ekoteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-96100.
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This thesis is an attempt to analyze and interpret the behavior of the two elements arsenic and phosphorus when released into the environment. Both of them may occur naturally in the environment but also may be added to the environment for certain purposes e.g. as pesticides and fertilizers respectively or through anthropogenic sources. When in excess, arsenic can be toxic to plants and organisms in the soil and some of it when leaches to groundwater or transported to surface water bodies through runoffs may pose a threat to aquatic organisms. Likewise, phosphorus when in excess result into eutrophication of surface water bodies and groundwater as well which has been a major problem in the Baltic Sea. In order to be able to predict their mobility a study on their chemical and physical characteristics under different conditions is important. The soil composition is an important aspect of nutrient management because some of the minerals present i.e. hydr(oxides) of aluminium and iron tend to hold and store both arsenic and phosphorus in the soil, while plant uptake and harvest may remove them (especially phosphorus) from the soil. This study was focused on Swedish agricultural soils and the samples for investigation were collected from two locations, one is Broknäs from which samples were collected from different horizons i.e. A 0-30 cm, C 60-90 cm and C 47-67 cm samples from an area known as Bogesundslandet, NE of Stockholm (59°24’N, 18°18’E) and E21:2 was collected from the county of Östergötland (58°27’N,14°57’E), southern Sweden not far from Lake Vättern, from where the A horizon was collected. Batch experiments were performed to check pH and concentration dependence of the sorption/desorption of As and P. Two varieties of the Freundlich equation (Basic and Competitive) were used to model the results obtained. It was observed that the dependence of arsenate and phosphate sorption/desorption on pH show a similar but not identical trend for both anions. At low pH, the dependence of dissolved P and As did not agree, for unknown reasons. Possibly, the low pH value may mobilize otherwise un-reactive P that at higher pH are blocked by some aluminium/iron precipitate. The Freundlich modeling results showed that there is direct competitive adsorption between As and P ions, at least in the A horizon. However use of the competitive Freundlich equation did not result in meaningful results in the C horizon, which may indicate different As and P sorption mechanisms. However, further studies on this are recommended.
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Lee, Nang Lap. "Analytical, centrifuge and numerical modelling of underwater vacuum consolidation of soft clay /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202007%20LEEN.
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Breen, L. "Re-modelling clay : ceramic practice and the museum in Britain (1970-2014)." Thesis, University of Westminster, 2016. https://westminsterresearch.westminster.ac.uk/item/9x230/re-modelling-clay-ceramic-practice-and-the-museum-in-britain-1970-2014.
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This thesis analyses how the dialogue between ceramic practice and museum practice has contributed to the discourse on ceramics. Taking Mieke Bal’s theory of exposition as a starting point, it explores how ‘gestures of showing’ have been used to frame art‑oriented ceramic practice. Examining the gaps between the statements these gestures have made about and through ceramics, and the objects they seek to expose, it challenges the idea that ceramics as a category of artistic practice has ‘expanded.’ Instead, it forwards the idea that ceramics is an integrative practice, through which practitioners produce works that can be read within a range of artistic (and non-artistic) frameworks. Focusing on activity in British museums between 1970 and 2014, it takes a thematic and broadly chronological approach, interrogating the interrelationship of ceramic practice, museum practice and political and critical shifts at different points in time. Revealing an ambiguity at the core of the category ‘ceramics,’ it outlines numerous instances in which ‘gestures of showing’ have brought the logic of this categorisation into question, only to be returned to the discourse on ‘ceramics’ as a distinct category through acts of institutional recuperation. Suggesting that ceramics practitioners who wish to move beyond this category need to make their vitae as dialogic as their works, it indicates that many of those trying to raise the profile of ‘ceramics’ have also been complicit in separating it from broader artistic practice. Acknowledging that those working within institutions that sustain this distinction are likely to re-make, rather than reconsider ceramics, it leaves the ball in their court.
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Muleya, Franco. "Modelling wheeled construction plant performance in clay and sandy terrain : a terramechanics perspective." Thesis, Anglia Ruskin University, 2014. http://arro.anglia.ac.uk/550362/.
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This research has investigated the effect of tyre rutting of wheeled construction plant performance traversing in wet and deformable terrain, specifically clay and sand. The purpose was to translate the wheel rutting into performance reduction measured in drawbar-pull. The ultimate goal was to translate the power loss into practical effects on cost, time and other economic variations on construction projects that are characterised by movement of wheeled plant on long haulage deformable roads. In order to achieve this aim, mathematical modelling was deployed based on Newton’s laws of motion, principles of energy conservation and numerical integration. The model is based on a single rigid wheel because construction plant tyres are inflated to high pressure in order to support heavy loads thereby translating the flexible tyres into rigid mode. The results from the mathematical model were verified using a three stage robust verification process which included computational analysis based on two existing semi-empirical methods and real experimental data. Laboratory experiments using Mobility SF- 3713 were also used to check the validity of the results. The results from the mathematical model verify that a flexible tyre can operate in rigid mode if it encounters softer and wet ground. Results further indicate that the soil cohesion, angle of shearing resistance and moisture content play key roles in the subsequent power loss created by motion resistance. All the results from computational analysis and the experiments were found to be consistent with the mathematical model results. The study concludes that there is ample evidence to suggest that there is significant power loss associated with wheeled construction plant traversing in soft terrain which can be assessed. The study further concludes that a combination of economic decisions on variables must be considered with respect to existing ground conditions. This will considerably reduce uncertainty levels in cost and resource management on construction projects.
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Montalti, Luca. "Heave of large excavations in clay: modelling and analysis of two british case-histories." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2010. http://amslaurea.unibo.it/1166/.
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ABSTRACT
Il presente lavoro vuole introdurre la problematica del rigonfiamento del terreno a seguito di grandi scavi in argilla.
Il sollevamento del terreno dopo lo scavo può passare inosservato ma sono numerosi i casi in cui il rigonfiamento dura per molti anni e addirittura decenni, Shell Centre, London, Lion Yard, Cambridge, Bell Common, London, ecc.
Questo rigonfiamento il più delle volte è impedito dalla presenza di fondazioni, si genera quindi una pressione distribuita che se non considerata in fase di progetto può portare alla fessurazione della fondazione stessa.
L’anima del progetto è la modellazione e l’analisi del rigonfiamento di grandi scavi in argilla, confrontando poi i risultati con i dati reali disponibili in letteratura.
L’idea del progetto nasce dalla difficoltà di ottenere stime e previsioni attendibili del rigonfiamento a seguito di grandi scavi in argilla sovraconsolidata.
Inizialmente ho esaminato la teoria e i fattori che influenzano il grado e la velocità del rigonfiamento, quali la rigidezza, permeabilità, fessurazione, struttura del suolo, etc. In seguito ho affrontato lo studio del comportamento rigonfiante di argille sovraconsolidate a seguito di scarico tensionale (scavi), si è evidenziata l’importanza di differenziare il rigonfiamento primario e il rigonfiamento secondario dovuto al fenomeno del creep.
Il tema centrale del progetto è l’analisi numerica tramite Flac di due grandi scavi in argilla, Lion Yard, Cambridge, e, Bell Common, London.
Attraverso una dettagliata analisi parametrica sono riuscito a trovare i migliori parametri che modellano il comportamento reale nei due casi in esame, in questo modo è possibile arrivare a stime e previsioni attendibili del fenomeno rigonfiante del terreno a seguito di grandi scavi.
Gli scavi modellati Lion Yard e Bell Common sono rispettivamente in Gault Clay e London Clay, grazie a famosi recenti articoli scientifici sono riuscito a evidenziare la principali propietà che diversificano i due terreni in esame, tali propietà sono estremamente differenti dalle normali caratteristiche considerate per la progettazione in presenza di terreno argilloso; sono così riuscito a implementare i migliori parametri per descrivere il comportamento dei due terreni nei diversi modelli.
Ho inoltre studiato l’interazione terreno-struttura, la pressione esercitata dal rigonfiamento del terreno è strettamente funzione delle caratteristiche di connesione tra fondazione superficiale e muro di sostegno, tale pressione non deve essere ignorata in fase progettuale poichè può raggiungere importanti valori.
Nello scavo di Lion Yard, considerando la presenza delle fondazioni profonde ho evidenziato il fatto che il rigonfiamento crea una forza distribuita di taglio tra i pali di fondazione ed il terreno, anche tale sollecitazione dovrebbe essere considerata ai fini della progettazione.
La problematica non si ferma solo sull’interazione terreno-fondazioni, infatti durante gli scavi di importanti fondazioni londinesi lo scarico tensionale ha creato uno spostamento significativo positivo verso la superfice di tratti di tunnel della metropolita, questo fenomeno può creare seri problemi di sicurezza nella rete dei trasporti pubblici.
Infine sono stati messi a confronto i risultati del programma Flac con quelli di metodi semplificati, ho trovato che utilizzando il metodo iterativo di O’Brien i risultati sono simili alla realtà e il tempo di calcolo è molto inferiore di quello richiesto utilizzando Flac, 2-3 giorni.
In conclusione posso affermare che grazie ad una dettagliata analisi parametrica è stato possibile stimare il rigonfiamento del terreno, argilla sovraconsolidata, nei due casi analizzati.
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Jones, Brendon Ronald. "Geotechnical centrifuge modelling of the behaviour of a compressible clay horizon underlying a reinforced sand foundation." Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/40363.
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Basal reinforcement, where high tensile geogrids are employed beneath structures, is becoming an
increasingly accepted construction technique along the eastern coast of southern Africa. The presence
of compressible, soft, thin and shallow clay horizons usually associated with complex estuarine or
lagoonal deposits are a major consideration when using basal reinforcement as a founding technique.
Basal reinforcement involves the use of high tensile strength geogrids beneath a structure to form a
reinforced sand foundation. Deformation behaviour under loading is an important component of
stability analysis of earth structures. If reinforcement is used, the mechanisms become altered.
Geotechnical centrifuge modelling is a unique physical modelling technique, as it allows replication
of in situ stresses, which is most important because soil behaviour is a function of stress. This is
achieved by placing the model at the end of the centrifuge arm, and subjecting it to an increased
gravitational field, which creates the correct stress distribution in the model. Centrifuge modelling
provides an appropriate technique to observe the behaviour of compressible, soft, thin and shallow
clay horizons when basal reinforcement is utilized. An appropriate centrifuge model was constructed
and compared the behaviour of the clay horizon under unreinforced and reinforced conditions.
Reinforcement configurations were adjusted to observe the influence of additional geogrid layers, and
extension of the width of the reinforcement. It was found that deformation behaviour is distinctly
different between unreinforced and reinforced tests. Vertical deformation in the unreinforced test
localised to the region directly beneath the platform, with little lateral disturbance to the clay horizon
beyond the platform edge. As such, the sand directly beneath the platform acts as a deeper rigid
platform. The deformation behaviour of the clay horizon changes with the inclusion of reinforcement.
When reinforcement is included a wider portion of clay is deformed. The lateral width of this
deformation zone is controlled by the width of the reinforcement, as the applied load is spread. A
‘wide-slab’ effect is evident with an increase in the geogrid width, as the tensioned membrane-effect
is mobilised to increase the capacity of the reinforced foundation sand. This results in a wider portion
of the clay deforming. Addition of geogrid reinforcement to the sand foundation under a wide
platform load enhances deformation of the clay, but has the advantage of an increased load-bearing
capacity of the system. Furthermore, the addition of multiple layers of reinforcement contributes to
this increase in load-bearing capacity. Additionally, increasing the installation width of the
reinforcement contributes to an increased vertical load-bearing capacity. However, this resultant
increase is only mobilised after a certain amount of vertical displacement. This is likely due to the
reinforcement requiring a certain amount of vertical displacement to mobilise tension in order to
support the applied load. The behaviour of a thin compressible clay horizon changes with the
inclusion of reinforcement under a wide platform load. The deformation behaviour of the clay is
increased by additional layers of reinforcement as well as an increase in the width of the
reinforcement. However, the increase in deformation comes at the benefit of an increased vertical
load-bearing capacity of the reinforced foundation sand.Dissertation (MSc)--University of Pretoria, 2014.
gm2014
Geology
unrestricted
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Marx, David Hercules. "The optimal placement of geogrid reinforcement in landfill clay liners." Diss., University of Pretoria, 2017. http://hdl.handle.net/2263/60633.
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Continued population growth is placing strain on the waste disposal facilities available in South Africa. However, limited air space suitable for landfilling drives the need for alternative solutions such as piggyback landfills to expand the waste disposal capacity. This method entails building a new, fully lined, landfill on top of existing waste. However, the old underlying waste is prone settlement that can result in the cracking of new landfill clay liner.
Geogrid reinforcement have been successfully used in clay liners to mitigate cracking induced by waste settlement. This research focused on investigating of the optimal reinforcement strategy (ORS) of such a liner subject to settlement. The ORS entails the optimal position for geogrid reinforcement in a liner, and the stiffness to be used at that position, given a total reinforcement cost.
Firstly, the fracture behaviour of unreinforced clay liners was investigated by means of four point bending tests on clay beams. It was found that the fracture of this clay occurred in three stages: linear behaviour, followed by non-linear behaviour when micro-cracks forms and finally macro-cracks that opened once the peak load was reached.
Thereafter, the behaviour of geogrid-reinforced clay liners, subjected to differential settlement, was investigated with finite element analyses in ABAQUS. A number of key factors were varied and the resulting change in behaviour of the liners was observed. These were: the overburden stress applied, clay liner thickness, magnitude of central settlement and the width and shape of the settlement trough developing in the underlying waste body.
Based on the numerical results, a series of plane-strain centrifuge tests of reinforced clay liners subject to differential settlement were designed. An unreinforced liner, a liner reinforced at the bottom quarter, a liner reinforced at the top quarter and a liner reinforced at both the bottom and top quarters were tested. Laser scanner scans of the surface and strains calculated from digital image velocimetry results were used to compare the behaviour of the liners. Based on these results it is recommended that for optimal performance the available reinforcement should be divided between the top and bottom quarters of the liner to mitigate the effect of settlement.Volgehoude bevolkingsgroei in Suid-Afrika plaas bestaande rommelstortingsfasiliteite onder druk. ’n Tekort aan grond geskik vir die bou van stortingsterreine moedig die soektog na alternatiewe oplossings soos abba-stortingsterreine aan. Hierdie metode behels ’n splinternuwe stortingsterrein wat bo-op bestaande rommel gebou word. Versakking van die bestaande rommel kan egter veroorsaak dat krake vorm in die nuwe stortingsterrein se kleivoering wat daarop lê. Vorige navorsing het die vorming van krake in die kleivoerings al welgeslaagd verhoed deur van georoosters as versterking gebruik te maak. Die huidige studie het op daardie navorsing gebou deur die optimale versterkings strategie (OVS) te bepaal vir so ’n kleivoering wat vervorm onder versakking van die onderliggende rommel. Die OVS definieer beide die optimale versterkings posisie in ’n kleivoering, en die styfheid van die georooster wat in daardie posisie geplaas moet word, gegewe ’n sekere totale versterkingskoste. Eerstens was daar ondersoek ingestel na die kraakgedrag van onversterkte kleivoerings. Vierpuntbuigtoetse van kleibalkies was hiervoor gebruik. Die krake het oor drie fases gevorm: eerstens was daar lineêre gedrag tot en met mikro-krake gevorm het. Dit is gevolg deur nie-lineêre gedrag wat gelei het tot makro-krake. Sodra die makro-krake gevorm het, is die maksimum las bereik wat die klei kon ondersteun. Na afloop van die balkbuigtoetse was eindige element analises in ABAQUS uitgevoer om die gedrag van versterkte kleivoerings wat bo-op versakkende afval lê te ondersoek. Die spanning toegepas op die oppervlak van die kleivoerings, die dikte van die kleivoerings en die versakkingstrogwydte, -vorm en -diepte was gevarieer om die effek daarvan op die gedrag van die kleivoerings te ondersoek. Na aanleiding van die resultate van die numeriese analise is ’n reeks sentrifuge toetse van kleivoerings wat aan versakking onderwerp word uitgevoer. ’n Onversterkte kleivoering, kleivoerings versterk in die boonste en onderste kwarte, en een versterk in beide die boonste en onderste kwart was getoets. Die gedrag van die verskillende kleivoerings was vergelyk deur die oppervlaktekrake op te meet met ’n laserskandeerder. Verder is die vervorming van die kleivoerings bepaal vanaf die verplasing van die grondpartikels tussen opeenvolgende digitale foto’s. Na aanleiding van hierdie resultate word dit aanbeveel dat die beskikbare georooster versterking opgedeel moet word tussen die boonste en onderste kwart van die kleivoerings ten einde optimale gedrag te verseker indien versakking sou plaasvind.
Dissertation (MEng)--University of Pretoria, 2017.
Deutscher Akademischer Austausch Dienst (DAAD)
Geosynthetics Interest Group of South Africa (GIGSA)
National Research Foundation of South Africa (NRF)
Civil Engineering
MEng
Unrestricted
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Postill, Harry E. "Weather-driven clay cut slope behaviour in a changing climate." Thesis, Loughborough University, 2018. https://dspace.lboro.ac.uk/2134/35832.
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Long linear earthwork assets constructed in high-plasticity overconsolidated clay are known to be deteriorating due to long-term effects of wetting and drying stress cycles as a result of seasonal weather patterns. These stress cycles can lead to shallow first-time failures due to the mobilisation of post-peak strength and progressive failure. Design requirements of new earthworks and management of existing assets requires improved understanding of this critical mechanism; seasonal ratcheting. Incremental model development and validation to allow investigation of multiple inter-related strength deterioration mechanisms of cut slope behaviour in high-plasticity overconsolidated clay slopes has been presented. Initially, the mechanism of seasonal ratcheting has been considered independently and a numerical modelling approach considering unsaturated behaviour has been validated against physical modelling data. Using the validated model, the effects of slope geometry, design parameter selection and design life have been considered. Following this, an approach to allow undrained unloading of soil, stress relief, excess pore water pressure dissipation, seasonal ratcheting and progressive failure with wetting and drying boundary conditions has been considered. Hydrogeological property deterioration and the potential implications of climate change have been explored using the model. In both cases the serviceable life of cut slopes is shown to reduce significantly in the numerical analyses. Finally, a model capable of capturing hydrogeological behaviour of a real cut slope in London Clay has been developed and validated against long-term field monitored data. Using the validated model, a climate change impact assessment for the case study slope has been performed. The numerical analyses performed have indicated that seasonal ratcheting can explain shallow first-time failures in high-plasticity overconsolidated clay slopes and that the rate of deterioration of such assets will accelerate if current climate change projections are representative of future weather.
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Hu, Wei. "Physical modelling of group behaviour of stone column foundations." Thesis, Connect to e-thesis, 1995. http://theses.gla.ac.uk/817/.
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Thesis (Ph.D.) - University of Glasgow, 1995.Ph.D. thesis submitted to the Faculty of Engineering, Department of Civil Engineering, Unversity of Glasgow, 1995. Includes bibliographical references. Print version also available.
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Poorooshasb, Farrokh. "Centrifuge modelling of the dynamic embedment of a heat emitting projectile in normally consolidated clay." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254435.
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Rujikiatkamjorn, Cholachat. "Analytical and numerical modelling of soft clay foundation improvement via prefabricated vertical drains and vacuum preloading /." Access electronically, 2005. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20060523.123914/index.html.
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Salman, Marwan A. [Verfasser], and Siegfried [Akademischer Betreuer] Schmauder. "Multiscale modelling of nano-clay filled shape memory polymer foams / Marwan A. Salman ; Betreuer: Siegfried Schmauder." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2020. http://d-nb.info/120659053X/34.
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Brennan, Colin. "River Analysis and Climate Change: Continuous Prediction of Clay-Bed Erosion in Watts Creek." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/37042.
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Predicted future precipitation is downscaled and used to drive a hydrologic model to assess future erosion potential in a semi-alluvial clay-bed watercourse, Watts Creek. The 21 km2 watershed is predominantly urban, with overall impervious cover of 22%, and the remaining land use split between agricultural and forested areas. Continuous simulations for the open water year, excluding spring freshet (April 1st to October 31st) were performed using the SWMHYMO (Stormwater Management Hydrologic Model) lumped hydrologic modelling platform. A shear stress exceedance and stream power erosion routine was added to the platform to calculate erosion potential. To account for uncertainty in the collected data, nine different observed discharge data sets were used to calibrate the model, each leading to a distinct set of calibrated parameter values. The difference between the observed data sets lies in the choice of rating curves and the collection period. The 2041-2080 precipitation outputs of the fourth version of the Canadian Regional Climate Model (CanRCM4) ran under Representative Concentration Pathways (RCPs) 4.5 and 8.5 at the MacDonald Cartier International Airport were downscaled using quantile matching and then used as input to the hydrologic model. For each set of calibrated parameters, a cumulative effective work index (CWI) based on the reach-averaged shear stress was calculated for Watts Creek during the open water year using both the historic (1968 2007) and projected future (2041-2080) flows, using a bed material critical shear stress for entrainment of 3.7 Pa. Results suggest an increase of 75% (resp. 139%) under RCP4.5 (resp. RCP8.5) in CWI compared to historic conditions for the average measured bed strength. The work index increase is driven by an increased occurrence of above-threshold events, and more importantly by the increased frequency of large events. The predicted flow regime under climate change would significantly alter the erosion potential and stability of Watts Creek. A channel adjustment sensitivity analysis, which balances future erosion potential with historic potential, was implemented and indicated that the channel could widen in the future from the current bankfull width of 6.1 m to 8.2 m for RCP4.5 and 10.2 m for RCP8.5. Specific morphological behaviour should be investigated in more detail, particularly to assess if the governing erosion mechanism is seasonally dependent, perhaps incising during spring freshet and widening when the bed is vegetated in the summer.
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Martin, Christopher Michael. "Physical and numerical modelling of offshore foundations under combined loads." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:b582fb74-7a1b-4be9-884d-0daa9fda7c7b.
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In addition to vertical loads, the foundations of offshore structures are subjected to horizontal loads and overturning moments as a result of environmental (wind and wave) loading. The behaviour of circular footings on cohesive soil under conditions of combined vertical, horizontal and moment (V, H, M) loading is the primary concern of this thesis. A programme of physical model tests, involving combined loading of circular footings on reconstituted Speswhite kaolin, is reported. The shape of footing used is typical of the "spudcan" foundations of independent leg jack-up drilling platforms. Previous experience with combined loading of footings on sand has revealed that the observed load:displacement behaviour is best understood, and theoretically modelled, in terms of work hardening plasticity theory. The present tests on clay confirm this, and the results are interpreted to give empirical expressions for (i) the combined load yield surface in V:H:M space, and (ii) a suitable flow rule to allow prediction of the corresponding footing displacements (z, h, θ) during yielding. Extension to a complete plasticity model is achieved using theoretical stiffness factors to define elastic behaviour, and theoretical lower bound bearing capacity factors (derived specifically for this work) to define the size of the yield surface as a function of vertical penetration. The predictive capabilities of the numerical model are evaluated by retrospective simulation of various footing tests. Finally some plane frame structural analyses of a representative jack-up unit are described; some of these analyses incorporate the plasticity-based numerical model of spudcan footing behaviour under combined loads.
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Lee, Kok Kuen. "Investigation of potential spudcan punch-through failure on sand overlying clay soils." University of Western Australia. School of Civil and Resource Engineering, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0212.
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When a jack-up foundation is installed on seabeds consisting of a sand layer overlying soft clay, potential for 'punch-through' failure exists. This happens due to an abrupt reduction in bearing resistance when the foundation punches a block of sand into the underlying soft clay in an uncontrolled manner. This can lead to a sudden large penetration that can cause temporary decommissioning and even toppling of the unit. This research has addressed this problem with the aim of developing a practical design method for the jack-up industry to assess potential punch-through hazards. This objective has been achieved with the successful development of a new conceptual model for predicting the peak penetration resistance and a consistent method for constructing a complete resistance profile of spudcan foundations penetrating through sand into the underlying clay. The analytical basis of the new conceptual model follows the approach for silo analysis, and takes into account the stress level and dilatant response of sand. It is therefore a significant improvement over the punching shear and load spread models recommended in the current industry guidelines SNAME (2002), which do not consider the strength properties of the sand. To provide relevant experimental data for the new model, an extensive series of 30 continuous penetration tests were performed using the UWA drum centrifuge. These experimental results were retrospectively simulated using finite element (FE) analysis, in order to back-calculate the stress-level dependent friction and dilation angles in the sand during peak penetration resistance. The back-analysis showed that larger values of peak resistance gave lower friction and dilation angles, which is consistent with gradual suppression of dilatancy under high confining stress. When compared to published results from visualisation experiments, the FE analysis showed a similar failure mechanism during peak resistance, where a frustum of sand was forced into the underlying clay, with the outer angle reflecting the dilation in the sand. This has formed the basis of the new conceptual model. The performance of the new model in predicting the experimental peak resistance was compared with other existing analytical methods. Additional experimental results, including those already in the literature, were incorporated in the comparative study. It was found that the new conceptual model generally gave a good prediction of the experimental values, while the prediction from SNAME (2002) was conservative, with the predicted values being about half the experimental results on average. It was also shown that the new model could be modified to predict the post-peak penetration resistance in the sand layer. Finally, an analytical method for predicting the resistance profiles in the underlying clay was devised based on new bearing capacity factors developed through FE analysis. By joining the values of peak resistance, post-peak resistance and the resistance profile in the underlying clay, a complete simplified penetration resistance profile for spudcan foundations in sand overlying clay can be generated. The predicted profiles were shown to match the experimental results well.
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Xu, Longfei. "Mechanical behaviour of compacted earth with respect to relative humidity and clay content : experimental study and constitutive modelling." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSET005/document.
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La terre compactée est considérée comme un mélange granulaire dans lequel l'argile joue un rôle de liant mais cette dernière exhibe une forte interaction avec l'eau. Pendant la durée de vie en service, la terre compactée est soumise aux changements de l’humidité relative. En raison de ces changements des conditions ambiantes perpétuels, la teneur en eau dans la terre varie, impactant leur performance mécanique. Le présent travail a ainsi pour but d’étudier l’impact de l’humidité relative et de la teneur d'argile sur le comportement mécanique de la terre compactée. Il se réalisera au travers d’études expérimentales et d'une modélisation constitutive. Dans la première partie de cette thèse, quatre terres régionales de provenances et de teneurs d'argile différentes sont identifiées. Une étude comparative a été réalisée entre le double compactage statique et le compactage dynamique. En parallèle, trois types d'essais spécifiques : essais de succion par la méthode de papier-filtre, essais de retrait et essais d'absorption d'eau, ont été menés pour donner des indications préliminaires quant aux effets d'interaction entre l'eau et l'argile. Dans la deuxième partie, l’impact de l’humidité relative et de la teneur d'argile sur le comportement de cisaillement a été étudié, prenant en compte des cycles de chargement-déchargement. En adoptant une définition particulière de la contrainte effective de Bishop, il a également été observé que les états de rupture dans le plan (p'-q) pour tous les échantillons sont alignés approximativement à une ligne droite unique passant par l'origine, quelque soit la succion et la pression de confinement. Sur la base des résultats expérimentaux, un nouveau modèle constitutif a été développé pour la simulation du comportement mécanique de la terre compactée. Ce nouveau modèle a ainsi été formulé dans la cadre de la mécanique de l'endommagement des milieux continus et de la théorie de Bounding Surface PlasticityCompacted earth is regarded as a granular mixture in which clay plays a role of binder but it also exhibits an important interaction with water. During their service life, compacted earth can be subject to large changes in relative humidity. Those perpetual changes of environmental conditions induce continuous changes of water content of the earth that impact significantly its mechanical performances. The present work aimes at studying the mechanical behavior of compacted earth with respect to relative humidity and clay content. It involves an extensive experimental study and a constitutive modelling. In the first part of this thesis, four kinds of local earth are identified with different clay contents. A comparison of compaction method was then conducted between a double static compaction and dynamic compaction. Three types of specific tests: suction test by filter paper method, shrinkage test and sorption-desorption test were carried out, thereby providing a preliminary insight on the interaction effects between clay and water. In the second part, the impact of clay and moisture contents on the shear behavior of compacted earth was investigated taking into account loading-unloading cycles. Adopting a particular definition of Bishop's effective stress, failure states of all samples were observed to lie approximately on a unique failure line crossing the origin in the (p'-q) plane regardless of matric suction and confining pressure. Finally, based on the above experimental results, a new constitutive model was proposed, based on the theories of Bounding Surface Plasticity and continuum damage mechanics, aiming to simulate mechanical behaviour of compacted earth
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Hermansson, Linnea, and Rebecka Söderberg. "Modelling of a compensated foundation in GeoSuite Settlement." Thesis, KTH, Jord- och bergmekanik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-278541.
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The world today is constantly growing, creating a need of new roads and residential areas. New constructions lead to an increased load onto the soil, which can result in deformations when the soil layers underneath are compressed. To reduce the increased load on the soil, a compensated foundation can be used. This method is based on the principle that the load from the construction will be compensated by the excavated soil, often replaced by a lightweight material. As an example, this method can be used in areas with great clay layers and in sensitive projects where the rise of deformations can have undesirable consequences. It is of great importance to be able to understand the impact this method has on the soil and what long-term deformations that can be expected.GeoSuite Settlement is a tool for calculation of settlements and is frequently used in the Nordic industry of geotechnical engineering. In this study, the possibilities of modelling a compensated foundation in the software has been examined. Additionally, an analysis of parameters has been conducted in the aim of evaluating the importance of the parameters in the modelling process and the final results. Three different projects have been used as a basis, where one of them is a made-up case, based on the test site of Lilla Mellösa, and two actual cases designed by Structor Geoteknik Stockholm AB. Only one of these two projects have been completed, enabling post-construction measuring to be able to compare the calculated deformations with measured data, just about 16 months post-construction.Mainly three different approaches to the modelling of a compensated foundation has been studied in this work; unloading and loading, only loading corresponding to the total increase of load and with an edited soil profile adapted for a lightweight material (the description of the methods are to be found in Appendix 11.7). Similar patterns of deformations have been found in the results for the three methods, aside from one case where a slightly larger deformation occurred as a result of the lightweight material getting in contact with the underlying clay (instead of the filling/ dry crust). Based on this work, the simplest method is suggested to be used, i.e. only loading corresponding to the increased load.Due to the time limitations of this work, a decision to only study a few parameters in the analysis has been made and also to study them individually. Since the compressibility and creep characteristics of the clay is strongly dependent on the actual and former situation of the stress, the results of this parameter study are not directly applicable to any other case. However, this study clearly shows the importance of carefully evaluating the parameters of the clay, especially the preconsolidation pressure σ’c and the compressibility modulus M, which are important to obtain lifelike results. The importance of evaluating the time resistance value rS with respect to the current addition of stress has also been shown in this study. As expected, the groundwater level also plays an important role for the final settlements in the clay.Vi lever i en värld som ständigt växer och detta skapar ett behov av nya vägar och bostadsområden. Nya konstruktioner som leder till en ökad belastning på jorden, kan ge upphov till sättningar när underliggande jordlager komprimeras. För att reducera belastningen på jorden kan en kompensationsgrundläggning användas, vilken bygger på principen att lasten från konstruktionen kompenseras av bortschaktad jord som ofta ersätts av ett lättfyllnadsmaterial. Metoden kan till exempel tillämpas i områden med mäktiga lerlager samt i känsliga projekt där uppkomsten av sättningar kan få stora konsekvenser. För att kunna dimensionera dessa är det av stor vikt att förstå dess påverkan på jorden och vilka långsiktiga sättningar som kan väntas uppkomma till följd av den nya konstruktionen.GeoSuite Sättning är ett beräkningsverktyg för sättningsberäkningar som idag används flitigt inom geoteknikbranschen. I detta arbete har möjligheterna att modellera en kompensationsgrundläggning med hjälp av programvaran studerats. Dessutom har en parameterstudie genomförts i syfte att undersöka vilka parametrar som är av stor betydelse för modelleringen och dess resultat. Som grund har tre projekt använts, varav ett är ett påhittat fall där jordprofilen baserats på den i testområdet Lilla Mellösa, och två är verkliga projekt tillhörande Structor Geoteknik Stockholm AB. I ett av dessa projekt har även beräknade deformationer jämförts mot uppmätta deformationer, cirka 16 månader efter konstruktion.Denna studie har främst studerat tre tillvägagångssätt för modellering av en kompensationsgrundläggning; av- och pålast, endast pålast motsvarande total lastökning samt av- och pålast med en redigerad jordprofil som anpassats till lättfyllnadsmaterialet (metoderna beskrivs i Bilaga 11.7). Resultaten har visat på ett snarlikt sättningsförlopp för de tre metoderna, bortsett från ett fall där en något större sättning uppkom till följd av att lättfyllningen i jordprofilen kom i kontakt med underliggande lera (istället för fyllning/ torrskorpelera). Utifrån detta arbete rekommenderas därmed att använda den enklaste metoden med endast pålast.På grund av arbetets tidsbegränsning har endast ett antal parametrar inkluderats i parameterstudien, dessutom har de främst utvärderats separat. Vilka parametrar för jordens kompressions- och krypegenskaper som har störst påverkan på resultatet är starkt beroende av spänningssituationen i det aktuella fallet och resultaten från detta arbete är därmed inte direkt applicerbart på andra projekt. Tydligt är dock att en noggrann utvärdering av jordens parametrar som dess förkonsolideringstryck σ’c samt kompressionsmodul M är väsentligt för att erhålla verklighetstrogna resultat. Studien har även visat på vikten av att utvärdera lerors kryptal rS med hänsyn till den aktuella tillskottsspänningen. Även grundvattennivån har visat sig ha en betydlig påverkan på uppkomsten av sättningar.
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Lei, Xiaoqin. "Theoretical modelling of coupled chemo-hydro-mechanical behaviour of unsaturated expansive clays." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0074.
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Expansive clays used in engineering practice are usually unsaturated and are sensitive to chemical composition of the in-pore solution. To analyse the complex coupled problems involved, an efficient mathematical model which can account for these chemo-hydro-mechanical behaviours has been developed. In this thesis, expansive clays are conceptualised into three-phase multi-species porous media. Based on the modified mixture theory and irreversible thermodynamics, a thermo-electro-chemo-hydro-mechanical framework has been developed. The Clausius-Duhem inequality, which governs the dissipations associated with mechanical work, phase transformation, mass transport and thermal transport, is rigorously derived. Based on this thermodynamic framework, constitutive laws for bulk liquid and salt mass transport, free and adsorbed water inter-phase mass transfer, and the chemo-elastic-plastic deformations of soil skeleton have been developed. The model has been implemented into the FEM software Bil and validated by simulating available experimental data on Boom Clays. What’s more, the salt infiltration process into an unsaturated expansive clay layer has been simulated to illustrate the applicability of the modelArgiles gonflantes utilisées dans la pratique de l'ingénierie sont généralement insaturés et sont sensibles à la composition chimique de la solution dans les pores. Pour analyser les problèmes complexes couplés impliqués, un modèle mathématique efficace qui peut expliquer ces comportements chimio-hydro-mécanique a été développé. Dans cette thèse, argiles gonflantes sont conceptualisés dans triphasés multi-espèces de milieux poreux. Sur la base de la théorie de mélange modifié et thermodynamique irréversible, un cadre thermo-électro-chimio-hydro-mécanique a été développé. L'inégalité de Clausius-Duhem, qui régit les dissipations associés au travail mécanique, transformation de phase, le transport de masse et le transport thermique, est rigoureusement dérivée. Basé sur ce cadre thermodynamique, lois de comportement pour liquides en vrac et le sel de transport de masse, transfert de masse de l'eau entre en phase libre et adsorbé, et les déformations chimio-élastique-plastique de squelette du sol ont été développés. Le modèle a été mis en œuvre dans le logiciel FÉM Bil et validé en simulant les données expérimentales disponibles sur les argiles de Boom. Qui plus est, le processus d'infiltration de sel dans une couche d'argile gonflante insaturés a été simulée pour illustrer l'applicabilité du modèle
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Manivannan, Ganeshalingam Aerospace Civil & Mechanical Engineering Australian Defence Force Academy UNSW. "Viscoplastic modelling of embankments on soft soils." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Aerospace, Civil and Mechanical Engineering, 2005. http://handle.unsw.edu.au/1959.4/38743.
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A major instrumented geosynthetic reinforced approach embankment was constructed to 5.5 m elevation above ground, with prefabricated vertical drains, over a soft compressible clay deposit at Leneghan, Newcastle, Australia in May 1995. The field monitoring of settlements for over six years shows that the embankment manifests significant creep. The instrumentation, field performance and the finite element analyses for predicting the long-term performance of this embankment are described in this thesis. The maximum settlement of 1.1 m was observed one year after the completion of construction. However, the embankment continued to settle at a rate of 0.4 mm/day for the next 5 years. The horizontal displacements of 0.09-0.14 m at various locations and the maximum reinforcement strains of 0.67% were recorded. A numerical model was developed to perform a fully coupled large deformation elasto-viscoplastic finite element analysis for this performance prediction based on creep model proposed by Kutter and Sathialingam (1992). The foundation soil was modelled with creep material behaviour using six noded linear strain triangular elements. A well-documented case history ??? Sackville embankment, New Brunswick, Canada was analysed using this model as a benchmark problem and the model was found to predict all the behaviour characteristics reasonably well. The results obtained from finite element analysis using this model are shown to be in reasonable agreement with the observed performance of Leneghans embankment in terms of settlements, horizontal displacements, excess pore pressures and geosynthetic strains. But, the prediction of settlements was less than satisfactory beyond April 1999. Finite element analyses were performed to study the sensitivity of this embankment behaviour on the variation of hydraulic conductivity values and geosynthetic reinforcement properties. This sensitivity study indicated that the kv variation, the kh/kv ratio and the nominal values of geosynthetic properties adopted in the benchmark analysis are reasonable enough for the long-term behaviour prediction.
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Ahayan, Sanae. "A constitutive Model for natural Clays : From Laboratory Testing to Modelling of Offshore Monopiles." Thesis, Ecole centrale de Nantes, 2019. http://www.theses.fr/2019ECDN0027.
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La contribution des parcs éoliens offshore en termes d’énergie renouvelable ne cesse de croître. L’électricité produite notamment par les éoliennes en mer du Nord représente de ce fait une part importante de l’énergie consommée en Europe. Pourtant, les objectifs de la Commission Européenne en termes de transition énergétique à l’horizon de 2020 sont loin d’être réalisés sans l’optimisation des techniques existantes et le développement de technologies de plus en plus innovantes. Les monopieux sont les fondations les plus populaires dans l’industrie des éoliennes offshores. Ce sont des pieux larges supportant des éoliennes de fortes puissances et situées dans des eaux plus profondes. L’objectif général de cette thèse de doctorat est d’étudier les interactions solstructure des monopieux sous sollicitation latérale, fondés dans les sols argileux. Une attention particulière est donnée aux comportement du sol dans le but de modéliser finement le comportement des sols argileuxNowadays, offshore wind energy industry is developing exponentially, due to the significant contribution of the North Sea wind turbines energy production to the total consumed energy in Europe. Given that the EU's energy target is to increase the share of renewable energy by 2020, there is a great potential of the offshore wind energy applications towards this direction. In order to achieve this, the support of scientific research is crucial. Monopiles have been by far the most support structure for offshore turbines, nowadays becoming applicable also for complex site conditions. The main objective of this PhD thesis is to study the soil-foundation interaction problem for offshore wind turbines monopiles embedded in clays. We focus therefore on the numerical modelling of natural clay behavior. We aim to develop a constitutive model for clay soils, which allow developing new p-y curves that could be widely applied in offshore wind turbines monopiles
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Larsson, Martin. "Quantifying macropore flow effects on nitrate and pesticide leaching in a structured clay soil : field experiments and modelling with the MACRO and SOILN models /." Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1999. http://epsilon.slu.se/avh/1999/91-576-5489-1.pdf.
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Baxter, David. "Innovation in the design of continuous flight auger and bored displacement piles." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/5091.
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The field of pile design and construction in the United Kingdom is currently in a period of change. Not only are new processes and techniques being developed but also the legislative landscape is changing with the introduction of new Europe wide normative standards (BSI, 2004, 2007). This project sought to optimise pile design through better understanding and interpretation of ground conditions and of the pile-soil interaction for two pile types, continuous flight auger and bored displacement piles. Quantitative methods for interpreting and summarising previous knowledge and experience have been developed; the strata are divided into discrete bands and properties are represented with summary statistics. Experience and previous knowledge relating to the shear strength of London Clay have been quantified and presented using this approach. Furthermore, a straightforward tool has been provided for the implementation of such data into design; the previous knowledge and new site specific data are combined using Bayesian updating. Through use of this technique, the uncertainty associated with interpreting ground conditions from site data has been demonstrated to be reduced. The techniques described have been adopted into design practice within the sponsoring company. Bored displacement piles are a relatively new pile type. There is little published data or scientific understanding of the processes undergone by the soils during and after construction and the effect that these have on pile performance. This research identified the need for, and developed, a unified framework of descriptors for the various types of bored displacement pile and investigated the installation energy and performance of bored displacement piles in London Clay. The energy to construct the pile was observed to be highly variable and not directly related to capacity. Performance of bored displacement piles was observed to be similar to continuous flight auger piles of similar dimensions; typical values for the adhesion between bored displacement piles and the surrounding soil were established and these were comparable to those achieved by continuous flight auger piles. In addition, to enable the analysis of the probability of failure of a pile, the sources of variation have been investigated and the variability quantified. Besides the soil conditions, the dimensions of the pile, notably pile diameter, were found to be a significant source of variation.
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Xu, Wenjie. "Investigation of Gas Migration in saturated Argillaceous Rock." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-132511.
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Gas migration in saturated argillaceous rock is studied in this work. Dependent on the pressure level the gas transport process is controlled by different mechanisms. Gas injection tests have been carried to investigate the gas transport process in low permeable argillaceous rock. We focus on the Opalinus Clay, which has been widely researched and is important for searching possible host rock of the radioactive waste disposal. Gas injection tests at different scales (laboratory, in-situ borehole and in-situ tunnel test) are intensively investigated in this work. The measurements of the tests are analysed and interpreted with numerical modelling method.
A coupled multi-phase flow and mechanical model has been developed and implemented in the scientific computed codes OpenGeoSys (OGS). In the applied numerical model the relationship between capillary pressure and water saturation degree is described with van Genuchten model. The Darcy’s law is used for the phase flux, and the relative permeability of both water and gas phase is considered. The deformation process is calculated with elastic perfect-plastic model. The anisotropic hydraulic and mechanic behaviours of the Opalinus Clay are involved in the numerical model. The hydraulic anisotropy is controlled by the permeability tensor. The elastic deformation process is modelled by generalized Hooke’s law. The plastic behaviour is calculated with return mapping algorithm, and the anisotropy is considered with a so called microstructure tensor method. The permeability change during the gas injection is described using pressure dependent or deformation dependent approach. With considering the permeability evolution the measured data can be in the numerical model quantitatively represented, and test observations can be interpreted.
Under laboratory condition it can be determined that the specimen permeability is reduced during compression. The significant permeability increase takes places when the gas injection pressure higher than the confining pressure. By the in-situ tests damage zone can be generated due to the drilling of boreholes and tunnel. The highly permeable areas dominate the hydraulic process. Fluid flows through the damaged zone into the not sealed section, e.g. the seismic observation boreholes by the in-situ borehole tests and the section out of the megapacker by the in-situ tunnel tests.
In this work, the two phase flow controlled and pathway dilatancy controlled gas migration mechanisms are successfully simulated. The developed numerical model can be used to investigate the gas injection tests at different scales and conditions.
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Sane, Abdoul Razac. "Matériaux à base de phosphates pour le stockage thermique de l'énergie." Thesis, Ecole nationale des Mines d'Albi-Carmaux, 2017. http://www.theses.fr/2017EMAC0010.
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Le stockage d’énergie joue un rôle très important dans le secteur énergétique. Concernant le stockage thermique, il est indispensable pour le fonctionnement en continue des centrales solaires à concentration (CSP) ou pour la récupération des chaleurs perdues dans des installations industrielles. Il y a de nos jours un besoin urgent de nouveaux matériaux performants pour remplacer les matériaux conventionnels à base de nitrate pour un fonctionnement à haute température. La présente thèse porte sur le développement de nouveaux matériaux à base de phosphates pour le stockage de la chaleur sensible. C’est la première étude sur l’utilisation des phosphates dans le stockage de la chaleur. Deux approches ont été explorées : le développement des matériaux liquides et des matériaux céramiques monolithiques. Dans la partie des matériaux liquides, l’objectif est de développer des phosphates ayant le même principe de fonctionnement que les sels fondus. Un grand nombre de phosphates a été étudié et les premiers critères d’évaluation sont les températures de fusion, d’évaporation ou de décomposition et la stabilité thermique. Le ternaire M(PO)3 (M = Li, Na, K avec 33,3% molaire de chaque alkali) peut fonctionner à l’état liquide entre 390 et 850°C alors que l’acide polyphosphorique peut fonctionner jusqu’à 200°C (température de solidification restant à déterminer). Concernant les matériaux céramiques, l’étude sur les monolithes de phosphates purs montre des difficultés lors de la mise en forme et la médiocre performance mécanique de ces matériaux. Le travail s’est ensuite focalisé sur les mélanges argileux-sable/phosphates. L’ajout de phosphates est indispensable pour améliorer les propriétés thermiques et mécaniques des céramiques traditionnelles de terre cuite. L’influence de la température de cuisson, la nature des phosphates et la granulométrie des phosphates a été étudié. Les propriétés physiques, thermiques, mécaniques, thermophysiques, thermomécaniques et la stabilité thermique de ces céramiques ont été étudiées entre 30 et 1000°C. Les résultats obtenus ont montré la bonne compétitivité des céramiques à base du mélange argileux-sable/phosphates par rapport aux autres matériaux de stockage thermique solides tels que le béton, les roches naturelles...Le potentiel d’application de ces céramiques a été démontré par des tests de stockage de type thermocline à l’échelle pilote utilisant les meilleurs matériaux monolithiques et de l’air comme fluide caloporteur. Différents paramètres comme la température d’entrée (350 à 850°C) et le débit du fluide caloporteur ont été étudiés pour les deux phases de charge et de décharge. En parallèle, un modèle 1D a été développé avec COMSOL-multiphysics pour simuler des étapes de charges et de décharges. Le modèle décrit les échanges de chaleur entre le solide, l'air et la paroi et tient compte de tous les paramètres liés au stockage thermocline. Les résultats de simulation sont en bon accord avec les données expérimentales obtenues lors des tests à l'échelle pilote. Ce travail a montré de forts intérêts des matériaux à base de phosphates pour le stockage thermique à des différentes gammes de températures couvrant toutes les technologies CSP et la chaleur fatale industrielleEnergy storage plays a very important role in the energy sector. Concerning the thermal energy storage (TES), it is indispensable for the continuous operation of concentrated solar power plants (CSP) as well as for the recovery of waste heat from industrial facilities. However, there is currently an urgency to develop new TES materials in order to support nitrate-based molten salts, which are up-to-date the only commercial TES materials. This work aimed to develop new phosphate-based materials for sensible heat storage. This is the first study on the use of phosphates as heat storage material. Both liquid and solid phosphate-based materials were developed and their properties and performances in TES were investigated. For liquid materials, the goal is to design phosphates which have the similar operation principle to nitrate-molten salts. This means they are under liquid state when working as TES materials. Different alkali polyphosphates (M(PO)3, M = Li, Na, K) were studied and the first assessment criteria was the melting point, boiling point and thermal stability. Two potential materials were identified. The first one was the ternary mixture of alkali polyphosphates ( Li33.3 Na33.3 K33.3(PO)3 ) which exists under liquid form between 390 and 850°C. The second one was polyphophoric acid ( HPO3.n H2O ) which exist in liquid form up to 200°C. Its melting point will be determined. For solid phosphate-based materials, the utilization of a selected synthetic phosphate or raw phosphate ore without any additive met a major difficulty of shaping step, and the products obtained exhibited poor mechanical performances. The work is then focused on ternary mixtures of clay-sand/phosphates. With this concept, phosphates played the role of additives to improve the properties of traditional fired clay ceramics for TES purposes. Thus, a parametric study was carried out for different clay-sand/phosphate mixtures. The influence of the firing temperature, the nature of phosphates and the granulometry of phosphates were investigated. The physical, thermal, mechanical, thermophysical, and thermomechanical properties and the thermal stability were studied between 30 and 1000°C. The best product was made of 76.24 wt.% clay, 19.06 wt.% sand and 4.7 wt.% hydroxyapatite - a synthetic phosphate and 80 wt.% clay, 15 wt.% sand and 5 wt.% raw phosphate ore. They were competitive versus other solid TES materials such as concrete, natural rocks etc. The potential application of these ceramics was experimentally demonstrated by using a pilot-scale TES system with air as heat transfer fluid. Both charging and discharging phases were successfully repeated several times with various inlet air temperatures (from 350 to 850°C) and air flow rates. Finally, a dynamic 1D model was developed using Comsol Multiphysics software to simulate the charging and discharging phases of the pilot-scale TES tests. This model took into account the role of air, solid ceramic and reservoir wall and integrated all the parameters that impacted the temperature profile in the storage tank. The simulation results matched well with experimental data
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Nguyen, Thê Duong. "Étude du comportement au feu des maçonneries de briques en terre-cuite : approche expérimentale et modélisation du risque d'écaillage." Thesis, Paris Est, 2009. http://www.theses.fr/2009PEST1059/document.
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La compréhension du comportement des structures en maçonneries exposées au feu et la prédiction de leur résistance au feu, sont des besoins majeurs, exprimes par les industriels de la terre cuite, à cause du manque d’études disponibles. L’objectif de ce travail est de construire des outils numériques qui sont capables de prédire le comportement et la tenue au feu des murs de briques alvéolaires en terre cuite, porteurs ou non porteurs, montes avec joints épais en mortier traditionnel ou avec joints minces en mortier colle. Pour cela, des investigations expérimentales à l’échelle de matériau et à l’échelle structurale sont menées permettant de comprendre les phénomènes thermo-hygro-mécaniques contrôlant la tenue au feu. Ces phénomènes majeurs sont par la suite pris en compte dans la construction de modèles de comportement, dont la mise en oeuvre numérique permet de disposer d’un outil de simulation de la tenue au feu des maçonneries. Pour le problème thermique, les trois modes de transferts : conduction, convection et rayonnement, avec l’ajustement de l’effet hydrique dans la capacité thermique, permettent de simuler la réponse thermo-hydrique dans la structure alvéolaire en terre cuite. Sur le plan mécanique, la tenue au feu des murs en maçonnerie est abordée du point de vue du risque d’écaillage. Cette rupture, localisée ou diffuse, des parois peut conduire à une perte d’étanchéité du mur ou à celle de son intégrité mécanique. Pour évaluer ce risque, une modélisation thermo-élastique tridimensionnelle est proposée avec la prise en compte de l’évolution des propriétés avec la température. Cette modélisation simplifiée est complétée à un critère d’écaillage de type détachement-voilement. En parallèle avec des calculs de validations, des études paramétriques sont menées afin d’identifier les influences des paramètres thermiques, mécaniques sur le comportement thermo-mécanique des mursUnderstanding the behaviour of masonry structures exposed to fire and prediction of their fire resistance, are nowadays one of the major needs, expressed by manufacturers of fire-clay, because of the lack of available studies. The objective of this work is to build numerical tools that are able to predict the behaviour and resistance to fire of walls made with hollow fire-clay brick. The walls may be loadbearing or unloadbearing, joined with thick traditional mortar or thin adhesive mortar. For this purpose, experimental investigations at material scale and structural scale are carried out to understand the thermo-hygro-mechanical phenomena controlling the fire resistance rate. These major phenomena are then taken into account for the construction of behaviour models, which allow to dispose a tool of simulation of fire behaviour of masonry. For the thermal problem, the three transfer modes : conduction, convection and radiation, with the adjustment of the water effect in the heat capacity, can simulate the thermo-hygric response of alveolar structure in the fire-clay. On the mechanical problem, the fire resistance of masonry walls is approached from the point of view of the risk of spalling. This rupture, local or diffuse, of the brick partitions can lead to a loss of integrity or of loadbearing capacity. To evaluate this risk, a three-dimensional thermoelastic modeling is proposed with the taking into account of the evolution of the properties with the temperature. This simplified modeling is completed with a criterion of spalling of type detachment-buckling. In parallel with the validated calculations, parametrical studies are conducted to identify the influence of thermal, mechanical on the thermo-mechanical behaviour of the walls
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Baudet, Beatrice Anne. "Modelling effects of structure in soft natural clays." Thesis, City University London, 2001. http://openaccess.city.ac.uk/8394/.
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Geological processes give natural clays a different structure to that of clays that are reconstituted in the laboratory. In soft clays, this structure often breaks down under loading; this is called destructuration. This project aimed to develop a model to predict destructuration in soft natural clays. An understanding of the main characteristics of the behaviour of these clays detained was from data reported in the literature. Existing frameworks that describe the behaviour of these clays were reviewed, and basic concepts proposed to model structured soils. The Sensitivity framework (Cotecchia & Chandler, 2000) uses sensitivity as a parameter that can represent structure in both volumetric and stress space before significant destructuration takes place. Study of the behaviour of three soft clays with low to medium sensitivities; Sibari, Bothkennar and Pisa clays, demonstrated that sensitivity changes in parallel with destructuration during both volumetric compression and undrained shearing such that there is a single expression that directly relates change in normalised sensitivity to change in damage strain, where the increment of damage strain is the magnitude of the vector of plastic strain increment. This destructuration law was used to extend an existing model, the Three-surface kinematic hardening (3-SKH) model which was developed by Stallebrass & Taylor (1997) for reconstituted clays. The new model requires only three new parameters to represent structure and its degradation that can each be derived from data from a single isotropic compression test. They are: the initial sensitivity, which represents the initial degree of structure in the natural clay; the ultimate sensitivity, which represents the stable elements of structure in the clay; and the parameter k, which controls the rate of destructuration with plastic strains. The other parameters used are the same as in the 3-SKH model and are derived from data from tests on the corresponding reconstituted clay. The model was evaluated against data from tests on Bothkennar and Pisa clay. Qualitatively, the model could predict the important features of behaviour observed in these clays. Quantitatively, results of analyses showed that determining initial sensitivity in a consistent way by using the Sensitivity framework leads to predicted values of undrained shear strength within 10 to 20% of the experimental values. Typically destructuration was correctly predicted in analyses simulating volumetric compression, but it was over-predicted by about 15 to 25% in analyses simulating undrained tests. This could be improved in some cases by using an ultimate sensitivity greater than unity in analyses simulating tests on specimens that are likely to have stable elements of structure arising from fabric. Structural anisotropy seemed to influence the behaviour of Pisa clay, and a model including structural anisotropy may improve predictions on such soils. The main limitation of the current research is the difficulty in determining the initial stress state and sensitivity to be used in the analyses; improvement of this should be the prime aim of further work.
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Jagercikova, Marianna. "Kinetic quantification of vertical solid matter transfers in soils by a multi-isotopic approach." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4307/document.
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Le lessivage du lutum (0-2 µm) est un de processus majeurs de la pédogenèse, qui a néanmoins été peu quantifié et modélisé. Ce processus ainsi que la bioturbation ont été quantifiés ici en couplant des différents systèmes isotopiques (137Cs, 210Pb (xs), 10Be atmosphérique, 206/207Pb, δ13C, 14C) à une modélisation numérique par une équation de diffusion-convection à paramètres variables avec la profondeur. Cette méthode originale a été appliquée sur des anthroposéquences de Luvisols développées sur du loess et différantes de par leur utilisation (culture, prairie ou forêt) et leurs pratiques agricoles (travail du sol, apport du fumier). Nos résultats montrent que 91 ± 9 % du 137Cs et 80 ± 9 % du 10Be sont associés au lutum et ainsi peuvent effectivement tracer des transferts verticaux de matière solide dans les sols à pH > 5 et à teneur en carbone organique faible. Le partage du plomb entre les différentes phases solides est plus complexe. En considérant deux compartiments pour les isotopes (macropores ou la matrice de sol), nous avons conçu un modèle multi-isotopique permettant de quantifier la contribution des transferts de matière solide à la distribution verticale de la fraction 0-2 µm actuelle. Le lessivage est responsable de 9 à 66 % de l'accumulation de lutum dans l'horizon Bt. Le coefficient de diffusion permet de quantifier le taux de mélange par la bioturbation. La modélisation multi-isotopique est une méthode de prédilection pour les études modernes de la pédogenèse et des processus de la zone critiqueClay translocation is one of the major soil forming processes, howeverit is poorly quantified and modeled. We propose to quantify it togetherwith bioturbation by combining different isotopic systems (137Cs , 210Pb (xs),meteoric 10Be, 206/207Pb, δ13C, 14C) with numerical modeling based on a nonlineardiffusion-convection equation with depth dependent parameters. Thisnovel method has been applied on Luvisol anthroposequences developed onloess, differing by their land use (cropping versus grassland or forest) andtheir agricultural practices (reduced tillage, no tillage and manure input).Our results show that as much as 91 ± 9 % and 80 ± 9 % of 137Cs and10Be, respectively, are associated to the clay size fraction (0-2 µm) and canthus effectively trace vertical solid matter transfers in soils with pH > 5 andlow organic carbon. Lead partitioning between different solid phases is morecomplex. Considering two spatial distributions of isotopes (macropores or soilmatrix), we built up a multi-isotopic modelling approach that simulates theexperimental data with the common set of transfer parameters and allowedus to quantify the relative contributions of vertical solid matter transfers topresent-day 0-2 µm vertical distributions. Clay translocation is responsiblefor 9 to 66 % of the clay accumulations in the Bt-horizon. The diffusion coefficientalso quantifies the rate of soil mixing by bioturbation. Modeling of thekinetics of solid matter transfer at multiple spatio-temporal scales should becomea method of predilection in modern pedogenic and critical zone studies
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Freitas, Teresa Maria Bodas. "Numerical modelling of the time dependent behaviour of clays." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/8370.
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In the last two decades extensive research has been undertaken to characterize the time and rate dependent response of soils and to describe it by means of a constitutive model. However, most of these constitutive equations have been dev.eloped for a single stress point and limited stress paths, and in engineering practice the time, dependent nature of soils is still commonly reduced to a single coefficient of secondary consolidation obtained from a 24h oedometer test. J This thesis describes the development and implementation, in the Imperial College Finite Element Program (I~FEP), of two elastic visco-plastic models based on the overstress theory to describe the stress-strain-time/rate behaviour of clayey soils. The models differ essentially in the adopted law to describe the variation of the creep ~ deformation with time. The fIrst model - Creep Model 1 - incorporates a linear logarithmic law to describe the variation ofthe creep defon:nation with time, while the second model- Equivalent Time (ET) Model - incorporates a non-linear logarithmic creep law, with a limit to the amount of volumetric creep strain that can occur. The implementation and performance of the models is validated through a series of simple fInite element analyses that mimic common l~boratory stress paths and show that the models are able to reproduce the' phenomena of primary and secondary compression, stress relaxation, primary and secondary creep and persistent rate effects on the stress-strain .response under Ko and triaxial stress conditions. The ET model is then used to investigate the increase in bearing capacity of preloaded footings on soft clay, taking into account both the effects of consolidation and soil hardening due to creep with time. Finally, a series of fInite element analyses are presented that mimic the loading tests performed on two instrumented rigid footings at the Bothkennar test site. These analyses highlight the importance of considering the soil viscous effects in engineering practice and the need to account for the soil creep non-linearity if good predictions of the long-term settlements of geotechnical structures are to be made.
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Ruiz, Restrepo Daniel Felipe. "Hydro-mechanical analysis of expansive clays : constitutive and numerical modelling." Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/669205.
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Bentonite-based materials are being currently considered in several countries as a backfill component in the multi-barrier concept for deep geological disposal of radioactive waste. The bentonite barrier fulfils several important functions: i) high swelling capacity to fill gaps and compress the excavation damaged zone and ii) very low hydraulic conductivity and important retention capacity which retards significantly radionuclides transport. Small-scale testing in geotechnical laboratories and in-situ experiments in underground research laboratories (URL) have demonstrated that initial state, water supply conditions and volume constrictions are the main aspects affecting the behaviour of bentonites.
In this context, the main objective of the present study is the numerical simulation of the hydro-mechanical behaviour of expansive clays. For this purpose, a constitutive model has been developed to characterise the bentonite-based materials. The modelling of these materials is a quite challenging task. They exhibit a marked double-porosity system in which the swelling/shrinkage mechanism occurs at clay aggregate level and the collapsible behaviour comes from granular-like skeleton formed by the aggregates. In addition, several material configuration, with even more intricate fabric, have been proposed for the emplacement works of seals and plugs. The explicit consideration of two structural levels for the constitutive model seems to be suitable. Mechanical interaction and water mass exchanges between them can explain the short- and long-term behaviour. The model has been formulated using concepts of elasto-plasticity for strain hardening materials and generalized plasticity theory. The formulation has been implemented in the finite element code program CODE-BRIGHT and has been used to solve a variety of problems. The results provide relevant insights into the hydro-mechanical behaviour of double structure porous media, and they indicated the main aspects affecting the responses of expansive barriers. In particular, the relevance of the structural levels interaction has been demonstrated.
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Sellers, E. J. "Constitutive modelling of the behaviour of clays under cyclic loading." Master's thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/8317.
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Includes bibliography.This research work involved the implementation of a constitutive model based on plasticity theory to model the behaviour of a clay under cyclic loading. The modelling must be based on an understanding of the soil response and the critical state theory provides a description of the soil response which then be formulated in terms of plasticity theory. A literature review showed that there is a shortage of information on the behaviour of soils under cyclic loading. Constitutive models for 'cyclic loading are discussed to compare the predictions and thus select a model.
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Phillips, John Wilfrid. "Mathematical and physical modelling of a floating clam-type wave energy converter." Thesis, University of Plymouth, 2017. http://hdl.handle.net/10026.1/8641.
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The original aim of the research project was to investigate the mechanism of power capture from sea waves and to optimise the performance of a vee-shaped floating Wave Energy Converter, the Floating Clam, patented by Francis Farley. His patent was based on the use of a pressurised bag (or ‘reservoir’) to hold the hinged Clam sides apart, so that, as they moved under the action of sea waves, air would be pumped into and out of a further air reservoir via a turbine/generator set, in order to extract power from the system. Such “Clam Action” would result in the lengthening of the resonant period in heave. The flexibility of the air bag supporting the Clam sides was an important design parameter. This was expected to lead to a reduction in the mass (and hence cost) of the Clam as compared with a rigid body. However, the present research has led to the conclusion that the Clam is most effective when constrained in heave and an alternative power take-off is proposed. The theoretical investigations made use of WAMIT, an industry-standard software tool that provides an analysis based on potential flow theory where fluid viscosity is ignored. The WAMIT option of Generalised Modes has been used to model the Clam action. The hydrodynamic coefficients, calculated by WAMIT, have been curve-fitted so that the correct values are available for any chosen wave period. Two bespoke mathematical models have been developed in this work: a frequency domain model, that uses the hydrodynamic coefficients calculated by WAMIT, and a time domain model, linked to the frequency domain model in such a way as to automatically use the same hydrodynamic and hydrostatic data. In addition to modelling regular waves, the time domain model contains an approximate, but most effective method to simulate the behaviour of the Clam in irregular waves, which could be of use in future control system studies. A comprehensive series of wave tank trials has been completed, and vital to their success has been the modification of the wave tank model to achieve very low values of power take-off stiffness through the use of constant force springs, with negligible mechanical friction in the hinge mechanism. Furthermore, the wave tank model has demonstrated its robustness and thus its suitability for use in further test programmes. The thesis concludes with design suggestions for a full-scale device that employs a pulley/counterbalance arrangement to provide a direct connection to turbine/generator sets, giving an efficient drive with low stiffness and inherently very low friction losses. At the current stage of research, the mean annual power capture is estimated as 157.5 kW, wave to wire in a far from energetic 18 kw/m mean annual wave climate, but with scope for improvement, including through control system development.
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Chen, Pingan Carleton University Dissertation Engineering Civil and Environmental. "Modelling the effects of lime-fly ash columns installed in soft clays." Ottawa, 1995.
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Bernard, Ellina. "Magnesium silicate hydrate (M-S-H) characterization : temperature, calcium, aluminium and alkali." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCK025/document.
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Les différentes options envisagées par la France et la Suisse pour le stockage de déchets radioactifs en couches géologiques profondes argileuses prévoient l’utilisation d’importants volumes de matériaux cimentaires. Les liants dits bas-pH ont été développés afin de limiter la perturbation de la roche encaissante par le panache alcalin. Les études expérimentales menées sur les interfaces béton bas-pH-argile mettent systématiquement en évidence la formation de phases silico-magnésiennes, potentiellement de silicate de magnésium hydraté (M-S-H), mal modélisées à cause de données thermodynamiques limitées. Cette étude a pour objectif de caractériser ces phases en température, en présence d’aluminium, calcium et d’alcalins pour alimenter les bases de données thermodynamiques et améliorer les calculs sur les évolutions physico-chimiques des bétons bas pH et éventuellement des bétons de Portland. Des suspensions de M-S-H ont été synthétisées à partir d'oxyde de magnésium et de fumée de silice à différentes températures, à différents temps de réaction et différents rapports Mg/Si. Un panel de techniques d’analyses de chimie du solide et des mesures en suspensions couplées à des analyses des phases liquides a été utilisé pour caractériser les phases synthétisées. Initialement, et quel que soit le Mg/Si total choisi pour la synthèse, un M-S-H avec un rapport Mg/Si ~1 précipite en présence de brucite et de silice amorphe. Lorsque l’équilibre du système est atteint, 2 à 3 ans à 20 °C ou 1 an à 50 et 70 °C, le Mg/Si varie de ~0,8 à ~1,4. La température a peu d'influence sur le M-S-H formé même si le M-S-H se forme plus rapidement et qu’il est légèrement moins stable thermodynamiquement lorsque la température augmente. A l'équilibre, sa structure mal définie est comparable à des nano-cristallites de phyllosilicates hydratés avec une surface spécifique supérieure à 200 m2/g. Un modèle de solution solide pour le M-S-H a été calculé et ajouté à la base de données.Dans un second temps, les travaux ont été focalisés sur la formation de M-S-H à partir de silicate de calcium hydraté (C-S-H) avec un faible Ca/Si (= 0,8) et de magnésium. Le C-S-H n’est pas stable à des pH avoisinant un pH = 10, ce qui favorise la précipitation de M-S-H. Des recherches détaillées montrent que du calcium peut être faiblement incorporé dans le M-S-H (Ca/Si ≤ 0,10), et des solutions solides contenant du calcium ont été ajoutés à la base de données. Pour des pH supérieurs à 10-10,5, les C-S-H et M-S-H coexistent. L’observation par MEB-EDS d’une interface en cellule de diffusion entre C-S-H (Ca/Si=0,8 représentant un liant bas pH) et M-S-H (Mg/Si=0,8), couplée à la modélisation de celle-ci en transport réactif, sur la base des nouvelles données thermodynamiques dérivées des expériences précédentes, montrent la détérioration rapide du C-S-H et la précipitation de M-S-H dans le disque C-S-H, ainsi qu’une absorption homogène du calcium dans le disque de M-S-H.L’augmentation du pH en solution favorise la sorption de cations. Des M-S-H présentant une sorption de sodium jusqu'à Na/Si ~ 0,20 en absence de brucite ont été observés à des pH avoisinants 12,5. La sorption sur le M-S-H est favorisée dans l'ordre Na+ < Mg2+ < Ca2+. Enfin, l'aluminium s’incorpore dans le M-S-H pour former du M-A-S-H. Un rapport Al/Si jusqu’à 0,2 est observé dans des suspensions synthétisées en présence d’aluminate de sodium ou de métakaolin. Les données de RMN de l’aluminium ont montré que celui-ci est présent dans les sites tétraédriques et octaédriques du M-A-S-H. La phase formée a une structure similaire à celle du M-S-H avec un degré de polymérisation des silicates et une charge effective de surface comparablesThe various options to store radioactive wastes in deep geological strata considered in France or Switzerland include the use of large volumes of cementitious materials for infrastructure in contact with argillaceous rocks. So-called low-pH binders were developed to minimize disruption to the surrounding rock by the alkaline plume. Studies conducted on the interaction zone between concrete and clay systematically highlighted the formation of magnesium silicate phases including magnesium silicate hydrate (M-S-H) at the interfaces, which can presently be modeled only partially due to incomplete thermodynamic data. The purpose of this study was to characterize these phases in temperature, aluminum, calcium, and alkali conditions in order to provide the thermodynamic data and improve the calculations on physicochemical evolutions of low-pH concretes and possibly Portland concretes.M-S-H phases were synthesized from magnesium oxide and silica fume in batch experiments at different temperatures, for various times and varying Mg/Si. A large number of different techniques such as chemical solid characterizations coupled with suspension investigations and liquid analyses were used to characterize the phases synthesized. Initially a M-S-H phase with Mg/Si equal to 1 was precipitated in addition to amorphous silica and brucite whatever the total Mg/Si used for the synthesis. After long equilibration times, 2 to 3 years at 20°C or 1 year at 50 and 70°C, the Mg/Si in M-S-H ranged from ~0.8 to ~1.4. The temperature had little influence on the M-S-H formed even if the M-S-H formation occurred faster and M-S-H was thermodynamically slightly less stable when the temperature was increased. At or near to equilibrium, M-S-H phases were characterized with ill-defined structure comparable to nano-crystallite, hydrated phyllosilicates with a surface area greater than 200 m2/g. A M-S-H solid-solution model was calculated and implemented in the thermodynamic database.It was observed that M-S-H also form from calcium silicate hydrate (C-S-H) with a Ca/Si = 0.8 in the presence of additional magnesium. In batch experiments, a low pH of the suspensions (pH ≤ 10) destabilized C-S-H or prevented its formation and favored the precipitation of M-S-H. Detailed investigations showed that small amounts of calcium could be incorporated in M-S-H (Ca/Si ≤0.10), such that also calcium containing end-members were added to the M-S-H solid-solution. At pH ≥ 10-10.5, two separate silicate phases coexist: C-S-H and M-S-H. The interface between a simplified “low-pH” binder mimicked by C-S-H with Ca/Si = 0.8 and a magnesium-rich environment mimicked by M-S-H with Mg/Si = 0.8 confirmed these phenomena. SEM-EDS observations and reactive transport modelling using the thermodynamic data derived in the batch experiments showed the fast deterioration of the C-S-H and the precipitation of M-S-H in the C-S-H disk at the interface and a homogeneous uptake of calcium in the M-S-H disk.The increase of pH favors the sorption. M-S-H with a sodium uptake up to Na/Si ~ 0.20 and without brucite formation were observed at high pH (12.5). The sorption on M-S-H was favored in the order Na+ < Mg2+ < Ca2+. Finally, aluminum was incorporated into M-S-H to form magnesium alumino-silicate hydrate (M-A-S-H). An Al/Si ratio up to 0.2 was observed in presence of sodium aluminate or metakaolin. 27Al MAS NMR data showed that aluminum was present in both tetrahedral and octahedral sites of M-(A-)S-H. The M-(A-)S-H formed had a similar structure as M-S-H with a comparable polymerization degree of the tetrahedral silicates and a similar surface charge