Numerical Analysis of Passive Force on Skewed BridgeAbutments with Reinforced Concrete WingwallsScott Karl SnowDepartment of Civil and Environmental Engineering, BYU Master of Science Historically bridges with skewed abutments have proven more likely to fail during earthquake loadings (Toro et al, 2013) when compared to non-skewed bridges (Apirakvorapinit et al. 2012; Elnashai et al. 2010). Previous studies including small-scale laboratory tests by Jessee (2012), large-scale field tests by Smith (2014), and numerical modeling by Shamsabadi et al. (2006) have shown that 45° skewed bridge abutments experience a reduction in peak passive force by about 65%. With numerous skewed bridges in the United States, this study has great importance to the nation's infrastructure.The finite element models produced in this study model the large-scale field-testing performed by Smith (2014), which was performed to study the significant reduction in peak passive resistance for abutments with longitudinal reinforced concrete wingwalls. The finite element models largely confirm the findings of Smith (2014). Two models were created and designed to match the large-scale field tests and were used to calibrate the soil parameters for this study. Two additional models were then created by increasing the abutment widths from 11 feet to 38 feet to simulate a two-lane bridge. The 45° skewed 11-foot abutment experienced a 38% reduction in peak passive resistance compared to the non-skewed abutment. In contrast, the 45° skewed 38-foot abutment experienced a 65% reduction in peak passive resistance compared to the non-skewed abutment. When the wingwalls are extended 10 feet into the backfill the reduction decreased to 59% due to the change in effective skew angle.The finite element models generally confirmed the findings of Smith (2014). The results of the 11- and 38-foot abutment finite element models confirmed that the wingwall on the obtuse side of the 45° skewed abutments experienced approximately 4 to 5 times the amount of horizontal soil pressure and 5 times the amount of bending moment compared to the non-skewed abutment. Increases in the pressures and bending moments are likely caused by soil confined between the obtuse side of the abutment and the wingwall.A comparison of the 11- and 38-foot 45° skewed abutment models showed a decrease in the influence of the wingwalls as the abutment widened. The wingwall on the acute side of the 38-foot abutment developed approximately 50% of the horizontal soil pressure compared to the 11-foot abutment. The heave distribution of the 11-foot abutment showed approximately 1- to 2-inches of vertical displacement over a majority of the abutment backwall versus more than half of the 38-foot abutment producing ½ an inch or less.

The aim of this Master Thesis is to assess the load carrying capacity of the Glomman Bridge outside of the Swedish city Örebro. The Glomman Bridge is an unreinforced concrete single span arch bridge with backfill. The bridge was constructed in 1923 on assignment from the Swedish National Railways (SJ). The failure criteria used in this thesis is that the bridge collapses when any cross section in the concrete arch reaches its ultimate capacity. In reality, the bridge may manage heavier loads than this. When the capacity is reached in a cross section, a hinge is formed and the arch relocates the forces to other parts of the arch that can carry higher stresses. The real bridge will not collapse until a fourth hinge is formed, and by that a mechanism. To be able to calculate the cross section forces in the arch, it was necessary to know the influences of the loads on the arch when they were run along the bridge. For this purpose, influence lines were obtained from a 2D finite element model created in ABAQUS, a general FE-analyses software. A calculation routine to find the least favourable load combination was then created in Matlab, a numerical calculation software. The routine was made to find the worst case among different load cases and to combine the standardized axle pressures with the present number of axles. A parametric survey was also performed because the material properties for the different parts of the bridge are very uncertain. In the survey, the initial values were changed one at a time to study the outcome on the load factor. The load factor is the ratio between the ultimate limit load and the actual load. The studied parameters are the compressive strength, the Young's modulus, the density and the Poisson's ratio of the different parts of the bridge. The parameters are studied individually irrespective of possible correlation. The studied parts of the bridge are the backfill, the arch, the abutments and the asphalt. The clearly most important component is found to be the backfill. With increased stiffness or increased Poisson's ratio in the backfill follows increased load factor. The equations behind the failure envelope can be derived from equilibrium equations for the unreinforced cross section. The influence lines are normalised with respect to the capacity of the cross section to get the degree of efficiency along the whole length of the arch, instead of the common influence lines that give the cross section forces. This is done because the failure is not caused by large cross section forces but by an exceeded ultimate stress. As the different loads are run along the bridge, the largest positive and negative efficiency for bending moment and normal force are localised. The normalised cross section forces are plotted together with the failure envelope and the load factor is then calculated. Several masonry arch bridges were loaded until collapse in a study performed by the British Transport and Road Research Laboratory. One of the bridges in the study, the Prestwood Bridge, has been used in this thesis as a comparison to the Glomman Bridge. The load carrying capacity of the Prestwood Bridge is known, and is used to verify that the method using the failure envelope is applicable. To compare the results from the cross section analysis from the failure envelope model to another method, the Glomman Bridge and the Prestwood Bridge were also tested in the commercial software RING 2.0. The method used in RING 2.0 differs from the failure mode in this thesis by calculating the load factor when four different cross sections reach their capacity and the bridge collapses. The failure envelope method allows an A/B-value (Axle- and Bogie load) of 102 kN/147 kN when using very poor values of the parameters and 181 kN/226 kN when using a reference case with normal parameters. Although the load capacity is found to be acceptable, the uncertainties are still large. To get a more accurate apprehension of the condition of the actual bridge, further research should be carried out, such as e.g. a non-linear model. / Syftet med föreliggande examensarbete är att uppskatta bärförmågan hos bron Glomman utanför Örebro. Glomman är en oarmerad betongvalvbro i ett spann med ovanliggande jordfyllning. Bron byggdes 1926 på uppdrag av Statens Järnvägar (SJ). Brottkriteriet i detta examensarbete är att bron går till brott när något tvärsnitt i betongbågen uppnår sin kapacitet. I själva verket är det möjligt att bron kan klara tyngre last än detta. När kapaciteten nås i ett tvärsnitt uppstår en led och bågen omlagrar krafterna till andra bågdelar som klarar större spänningar. Den verkliga bron rasar inte förrän en fjärde led har utvecklats, och därmed en mekanism. För att kunna beräkna tvärsnittskrafterna i bågen, var det nödvändigt att känna till trafiklasternas påverkan på bågen när de kördes över bron. För detta ändamål erhölls influenslinjer från en tvådimensionell finita elementmodell skapad i ABAQUS, ett generellt FE-program. En beräkningsrutin för att finna värsta tänkbara lastkombinering skapades i Matlab, ett numeriskt beräkningsprogram. Rutinen utformades för att hitta värsta fallet bland olika lastfall samt för att kombinera standardiserade axeltryck med det aktuella antalet axlar. En parameterstudie utfördes också då materialegenskaperna för de olika delarna i bron är mycket osäkra. I parameterstudien ändrades ingångsvärdena ett åt gången för att studera utslaget på lastfaktorn. Lastfaktorn är förhållandet mellan brottgränslasten och den verkliga lasten. De parametrar som studeras är tryckhållfastheten, E-modulen, densiteten och tvärkontraktionen för de olika brodelarna. Parametrarna studeras enskilt utan hänsyn till eventuell korrelation. De brodelar som studeras är fyllningen, bågen, fundamenten och asfalten. Den klart viktigaste komponenten visar sig vara fyllningen. Med ökad styvhet eller ökad tvärkontraktion i fyllningen följer ökad last­faktor. Ekvationerna bakom brottenveloppet kan härledas ur jämviktsekvationer för det oarmerade tvärsnittet. Influenslinjerna normeras med avseende på tvärsnittets kapa­citet för att få ut utnyttjandegraden längs hela bågen. Detta görs då det egentligen inte är för stor tvärsnittskraft som orsakar brott utan för stor spänning. Högsta och lägsta utnyttjandegrad för böjande moment och normalkraft lokaliseras när de olika typlasterna körs över bron. Utnyttjandegraderna placeras i brottenveloppet för att sedan räkna fram en lastfaktor. Ett flertal liknande broar har lastats till brott i en studie genomförd av British Transport and Road Research Laboratory. En av broarna i studien, Prestwood Bridge, har använts i denna rapport som jämförelse med Glomman. Då bärförmågan hos Prestwood Bridge är känd används den till att bekräfta att metoden med brott­enveloppet är tillämpbar. För att jämföra resultaten från tvärsnittsanalysen i brottenveloppmetoden med en annan metod, testades även Glomman och Prestwood Bridge i det kommersiella programmet RING 2.0. Metoden som används i RING 2.0 skiljer sig från brottmoden i denna rapport genom att istället beräkna lastfaktorn när fyra olika tvärsnitt har uppnått sina kapaciteter och bron kollapsar. Metoden med brottenvelopp tillåter ett A/B-värde (Axel- och Boggitryck) på 102 kN/147 kN när mycket dåliga parametervärden används och 181 kN/226 kN när referensfallet med normala parametervärden används. Även om bärförmågan kan anses vara acceptabel är osäkerheterna stora. För att få en nogrannare uppfattning om brons faktiska tillstånd bör fortsatta studier utföras, som t.ex. en icke-linjär modell.

Placement and compaction of the backfill behind an earth retaining wall may induce a vertical shear force at the soil-to-wall interface. This vertical shear force, or downdrag, is beneficial for the stability of the structure. A significant reduction in construction costs may result if the downdrag is accounted for during design. This potential reduction in costs is particularly interesting in the case of U.S. Army Corps of Engineers lock walls. A simplified procedure is available in the literature for estimating the downdrag force developed at the wall-backfill interface during backfilling of a retaining wall. However, finite element analyses of typical U.S. Army Corps of Engineers lock walls have shown that the magnitude of the downdrag force may decrease during operation of the lock with a rise in the water table in the backfill. They have also shown that pre- and post-construction stress paths followed by interface elements often involve simultaneous changes in shear and normal stresses and unloading-reloading. The hyperbolic formulation for interfaces (Clough and Duncan 1971) is accurate for modeling the interface response in the primary loading stage under constant normal stress. However, it has not been extended to model simultaneous changes in shear and normal stresses or unloading-reloading of the interface. The purpose of this research was to develop an interface model capable of giving accurate predictions of the interface response under field loading conditions, and to implement this model in a finite element program. In order to develop the necessary experimental data, a series of tests were performed on interfaces between concrete and two different types of sand. The tests included initial loading, staged shear, unloading-reloading, and shearing along complex stress paths. An extended hyperbolic model for interfaces was developed based on the results of the tests. The model is based on Clough and Duncan (1971) hyperbolic formulation, which has been extended to model the interface response to a variety of stress paths. Comparisons between model calculations and tests results showed that the model provides accurate estimates of the response of interfaces along complex stress paths. The extended hyperbolic model was implemented in the finite element program SOILSTRUCT-ALPHA, used by the U.S. Army Corps of Engineers for analyses of lock walls. A pilot-scale test was performed in the Instrumented Retaining Wall (IRW) at Virginia Tech that simulated construction and operation of a lock wall. SOILSTRUCT-ALPHA analyses of the IRW provided accurate estimates of the downdrag magnitude throughout inundation of the backfill. It is concluded that the extended hyperbolic model as implemented in SOILSTRUCT-ALPHA is adequate for routine analyses of lock walls. / Ph. D.

Gelfill (GF) is made of tailings, water, binder and chemical additives (Fillset, sodium silicate gel). The components of GF are combined and mixed on the surface and transported (by gravity and/or pumping) to the underground mine workings, where the GF can be used for both underground mine support and tailings storage. Thermal (T), hydraulic (H), and mechanical (M) properties are important performance criteria of GF. The understanding of these engineering properties and their evolution with time are still limited due to the fact that GF is a new cemented backfill material. In this thesis, the evolution of the thermal, hydraulic, mechanical, and microstructural properties of small GF samples are determined. Various binder contents of Portland cement type I (PCI) are used. The GF is cured for 3, 7, 28, 90, and 120 days. It is found that the thermal, hydraulic and mechanical properties are time-dependent or affected by the degree of binder hydration index. Furthermore, a relationship is found between the compressive strength and the saturated hydraulic conductivity of the GF samples. The unsaturated hydraulic properties of GF samples have also been investigated. The outcomes show that unsaturated hydraulic conductivity is influenced by the degree of binder hydration index and binder content, especially at low suction ranges. Simple functions are proposed to predict the evolution of air-entry values (AEVs), residual water content, and fitting parameters from the van Genuchten model with the degree of hydration index (α). Furthermore, two columns are built to simulate the coupled thermo-hydro-mechanical (THM) behaviour of GF under drained and undrained conditions. The obtained results from the GF columns are compared with the small samples. It is observed that the mechanical properties, hydraulic properties (suction and water content), and temperature development are strongly coupled. The magnitude of these THM coupling factors is affected by the size of the GF. The findings also show that the mechanical, hydraulic and thermal properties of the GF columns are different from samples cured in plastic moulds.

Gelfill (GF) is made of tailings, water, binder and chemical additives (Fillset, sodium silicate gel). The components of GF are combined and mixed on the surface and transported (by gravity and/or pumping) to the underground mine workings, where the GF can be used for both underground mine support and tailings storage. Thermal (T), hydraulic (H), and mechanical (M) properties are important performance criteria of GF. The understanding of these engineering properties and their evolution with time are still limited due to the fact that GF is a new cemented backfill material. In this thesis, the evolution of the thermal, hydraulic, mechanical, and microstructural properties of small GF samples are determined. Various binder contents of Portland cement type I (PCI) are used. The GF is cured for 3, 7, 28, 90, and 120 days. It is found that the thermal, hydraulic and mechanical properties are time-dependent or affected by the degree of binder hydration index. Furthermore, a relationship is found between the compressive strength and the saturated hydraulic conductivity of the GF samples. The unsaturated hydraulic properties of GF samples have also been investigated. The outcomes show that unsaturated hydraulic conductivity is influenced by the degree of binder hydration index and binder content, especially at low suction ranges. Simple functions are proposed to predict the evolution of air-entry values (AEVs), residual water content, and fitting parameters from the van Genuchten model with the degree of hydration index (α). Furthermore, two columns are built to simulate the coupled thermo-hydro-mechanical (THM) behaviour of GF under drained and undrained conditions. The obtained results from the GF columns are compared with the small samples. It is observed that the mechanical properties, hydraulic properties (suction and water content), and temperature development are strongly coupled. The magnitude of these THM coupling factors is affected by the size of the GF. The findings also show that the mechanical, hydraulic and thermal properties of the GF columns are different from samples cured in plastic moulds.

The work presented in this thesis comprises the assessment of existing arch bridges with overlying backfill. The main objective is to estimate the load carrying capacity in ultimate limit state analysis. A case study of the old Årsta railway bridge is presented, serving as both the initiation and a direct application of the present research. The demand from the bridge owner is to extend the service life of the bridge by 50 years and increase the allowable axle load from 22.5 to 25 metric tonnes. The performed analyses show a great scatter in estimated load carrying capacity, depending on a large number of parameters. One of the factors of main impact is the backfill material, which may result a significant increase in load carrying capacity due to the interaction with the arch barrel. Based on theoretical analyses, extensive conditional assessments and the demand from the bridge owner, it was decided that the bridge needed to be strengthened. The author, in close collaboration with both the bridge owner and the persons performing the conditional assessment, performed the development of a suitable strengthening. The analyses showed a pronounced three-dimensional behaviour, calling for a design using non-linear finite element methods. Due to demands on full operability during strengthening, a scheme was developed to attenuate any decrease in load carrying capacity. The strengthening was accepted by the bridge owner and is currently under construction. It is planned to be finalised in 2012. The application of field measurements to determine the structural manner of action under serviceability loads are presented and have shown to be successful. Measured strain of the arch barrel due to passing train has been performed, both before, during and after strengthening. The results serve as input for model calibration and verification of the developed strengthening methods. The interaction of the backfill was not readily verified on the studied bridge and the strengthening was based on the assumption that both the backfill and the spandrel walls contributed as dead weight only. The finite element models are benchmarked using available experimental results in the literature, comprising masonry arch bridges with backfill loaded until failure. Good agreement is generally found if accounting for full interaction with the backfill. Similarly, accounting for the backfill as dead weight only, often results in a decrease in load carrying capacity by a factor 2 to 3. Still, several factors show a high impact on the estimated load carrying capacity, of which many are difficult to accurately assess. This suggests a conservative approach, although partial interaction of the backfill may still increase the load carrying capacity significantly. / Arbetet i föreliggande avhandling omfattar analyser av befintliga bågbroar med ovanliggande fyllning. Huvudsyftet är att uppskatta bärförmågan i brottgränstillstånd. En fallstudie av gamla Årstabron redovisas, vilken utgör både initieringen och en direkt tillämpning av föreliggande forskning. Kravet från broförvaltaren är att öka brons livslängd med 50 år, samtidigt som axellasten ska ökas från nuvarande 22.5 ton till 25 ton. Utförda analyser visar på stor spridning i uppskattad bärförmåga, beroende på ett stort antal parametrar. En av de främsta faktorerna är fyllningens egenskaper, vilken kan resultera i en markant ökning av bärförmågan p.g.a. samverkan med bågen. Baserat på teoretiska analyser, tillståndsbedömningar och krav från broförvaltaren beslutades att bron skulle förstärkas. En förstärkningsmetod har utvecklats i nära samarbete med broförvaltaren och personer som tidigare utfört tillståndsbedömningarna. Analyserna visar ett utpräglat tredimensionellt beteende, vilket har föranlett användandet av icke-linjära finita elementmetoder. Krav på full trafik under samtliga förstärkningsarbeten har resulterat i att dessa utförs enligt en föreskriven ordning, som ska reducera minskning i bär­förmåga under samtliga etapper. Förstärkningsförslaget godkändes av Banverket och är för närvarande under byggnation. Enligt plan ska dessa slutföras under 2012. Fältmätningar har använts för att bestämma det statiska verkningssättet under brukslaster, vilket visas ge goda resultat. Resulterande töjningar från passerande tåg har uppmäts i bågen, både före, under och efter förstärkning. Resultaten har använts både för att kalibrera beräkningsmodeller och att verifiera utförda förstärkningar. Samverkan mellan båge och fyllning har inte kunnat verifierats för den aktuella bron och de utvecklade förstärkningarna baseras på en modell där både fyllning och sidomurar endast utgör yttre verkande last. De framtagna finita element modellerna har jämförts med experimentella resultat från litteraturen, omfattande tegelvalvsbroar med ovan­liggande fyllning belastade till brott. Generellt erhålls god överensstämmelse om full samverkan mellan båge och fyllning antas. Om fyllningen istället endast betraktas som yttre last, minskar lastkapaciteten ofta med en faktor 2 till 3. Fortfarande uppvisar ett antal faktorer stor inverkan på bärförmågan, vilka ofta är svåra att med säkerhet bestämma. Ett konservativt betraktningssätt rekommenderas, även om delvis sam­verkan med fyllningen fortfarande kan öka bärförmågan avsevärt. / QC 20110426

In questa tesi, l’analisi verte su risk-adjusted performance, proprietà statistiche e caratteristiche dei fondi hedge (FH). Nel primo articolo, i risultati relativi al survivorship bias e backfill bias indicano che l’impatto delle distorsioni è diverso a seconda delle strategie. Utilizzando il modello multifattoriale di Fung and Hsieh (2004), l’analisi della performance indica che il 42% dei FH ha ottenuto un rendimento superiore al mercato. Infine, utilizzando dei metodi parametrici e non parametrici, l’analisi della persistenza indica differenti livelli di persistenza a seconda della strategia. Nel secondo articolo, vengono analizzati i fondi di fondi hedge (FOHFs). I risultati sono particolarmente interessanti. In primo luogo, i FOHFs e le sotto strategie hanno generato un excess return positivo; inoltre l’alfa ottenuto attraverso il modello a 7 fattori di Fung and Hsieh (2004) risulta elevato. In secondo luogo, i FOHFs e le sotto strategie hanno un rendimento inferiore a quello dell’indice dei FH. In terzo luogo, le correlazioni tra gli indici dei FOHFs e l’indice azionario sono inferiori rispetto alle correlazioni tra l’indice dei FH e gli indici azionari. Infine, l’indice dei FH e quelli dei FOHFs sono positivamente correlati con l’indice azionario quando il mercato tende al ribasso, ma risultano non correlati con l’indice azionario quando il mercato tende al rialzo. Rispetto all’indice dei FH, gli indici dei FOHFs hanno una correlazione minore con gli indici azionari in entrambe le fasi del mercato, suggerendo che i FOHFs forniscono benefici maggiori in termini di diversificazione rispetto ai fondi hedge puri. / In this thesis, I examine the risk-adjusted performance, statistical properties and fund characteristics of hedge fund investments. In Essay One, results of survivorship bias and backfill bias by investment styles indicate that biases are different across styles. Using a multi-factor model of Fung and Hsieh (2004), the analysis of performance indicates that 42% of the hedge funds significantly outperformed the market. Finally, using parametric and non-parametric methods, the analysis of persistence indicates different degree of persistence depending on the hedge fund strategy. In Essay Two, I analyse fund of hedge funds (FOHFs). I find several interesting results. First, FOHFs and the sub-strategies earn positive excess returns and a high Fung and Hsieh 7-factor alpha. Second, FOHFs and the sub-strategies underperform the hedge fund index (HFI). Third, the correlations between FOHF indices and equity index are lower than correlations between HFI and equity indices. Finally, hedge funds and FOHFs are positively correlated with the equity index in the bear markets but uncorrelated with the equity index in the bull markets. Compared to HFI, FOHF indices have lower correlation with equity index in both bull and bear markets, indicating that FOHFs provide better diversification benefits than individual hedge funds.

Gelfill (GF) is made of tailings, water, binder and chemical additives (Fillset, sodium silicate gel). The components of GF are combined and mixed on the surface and transported (by gravity and/or pumping) to the underground mine workings, where the GF can be used for both underground mine support and tailings storage. Thermal (T), hydraulic (H), and mechanical (M) properties are important performance criteria of GF. The understanding of these engineering properties and their evolution with time are still limited due to the fact that GF is a new cemented backfill material. In this thesis, the evolution of the thermal, hydraulic, mechanical, and microstructural properties of small GF samples are determined. Various binder contents of Portland cement type I (PCI) are used. The GF is cured for 3, 7, 28, 90, and 120 days. It is found that the thermal, hydraulic and mechanical properties are time-dependent or affected by the degree of binder hydration index. Furthermore, a relationship is found between the compressive strength and the saturated hydraulic conductivity of the GF samples. The unsaturated hydraulic properties of GF samples have also been investigated. The outcomes show that unsaturated hydraulic conductivity is influenced by the degree of binder hydration index and binder content, especially at low suction ranges. Simple functions are proposed to predict the evolution of air-entry values (AEVs), residual water content, and fitting parameters from the van Genuchten model with the degree of hydration index (α). Furthermore, two columns are built to simulate the coupled thermo-hydro-mechanical (THM) behaviour of GF under drained and undrained conditions. The obtained results from the GF columns are compared with the small samples. It is observed that the mechanical properties, hydraulic properties (suction and water content), and temperature development are strongly coupled. The magnitude of these THM coupling factors is affected by the size of the GF. The findings also show that the mechanical, hydraulic and thermal properties of the GF columns are different from samples cured in plastic moulds.

Submitted by Pedro Silva Filho (pfsilva@ipen.br) on 2018-01-31T16:42:14Z No. of bitstreams: 0 / Made available in DSpace on 2018-01-31T16:42:14Z (GMT). No. of bitstreams: 0 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A deposição de rejeitos radioativos em repositórios geológicos profundos vem sendo estudada nos últimos anos em diversos países. Materiais à base de cimento são utilizados nesses repositórios como material estrutural, matriz de imobilização de rejeitos ou material de preenchimento. Compreender o desempenho desse material é essencial para garantir a segurança da instalação durante o seu tempo de vida útil (de milhares a centenas de milhares de anos, dependendo do tipo de rejeito). Este trabalho objetiva modelar o comportamento em longo prazo do cimento Portland e estudar a influência de diversos fatores na hidratação e na evolução desse material. A modelagem descritiva abordou a hidratação do cimento nas condições ambientais esperadas no repositório e os efeitos desses fatores em propriedades mecânicas, mineralógicas e morfológicas do cimento. Os fatores ambientais considerados relevantes neste trabalho foram: alta temperatura e pressão, penetração de água subterrânea contendo íons quimicamente agressivos ao cimento e a presença do campo de radiação proveniente dos rejeitos. Ensaios acelerados de degradação também foram realizados para corroborar com o modelo descrito. Observou-se uma sinergia entre diversos fatores na degradação do cimento, como a influência da temperatura e da radiação em reações deletérias ao material. O resultado da modelagem apontou três principais possíveis causas de falha nas barreiras artificiais: a) a formação de um caminho preferencial; b) a perda de resistência e coesão do material; e c) o aumento na corrosão das estruturas metálicas. A descrição do modelo apresentada é a base para a modelagem matemática e a análise de segurança dos repositórios estudados no Brasil. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP / CAPES:1231206

L’objectif de la thèse est de comprendre le comportement géochimique de l’arsenic dans les remblais miniers en pâte cimentés. Cette technique est employée depuis plusieurs années pour remblayer les galeries de mine exploitées à l’aide des rejets de concentrateurs. Pour cette étude, deux types de remblais sont élaborés en laboratoire : des échantillons de remblai minier en pâte synthétiques, fabriqués à partir de silice et enrichis artificiellement en arsenic, et des remblais miniers en pâte élaborés à partir de rejets miniers arséniés. Dans les deux cas, différents liants cimentaires sont testés. Plusieurs types d’investigations sont menés sur les échantillons de remblai en pâte cimentés. Une caractérisation minéralogique est effectuée à l’aide de divers outils. En parallèle, les échantillons de remblais sont soumis à différents tests de lixiviation complémentaires, afin d’évaluer la mobilité/rétention de l’arsenic dans ces matrices. Enfin, une modélisation géochimique est mise en œuvre à partir des résultats issus des deux études précédentes, afin d’affiner les connaissances sur la nature et la stabilité des composés arséniés dans les remblais étudiés. Les résultats obtenus indiquent que l’arsenic est mieux stabilisé dans les matrices à base de ciment Portland et de laitier de haut-fourneau que dans les remblais à base de cendres volantes. Le comportement à la lixiviation variable d’une matrice à l’autre s’explique par des spéciations et des mécanismes de piégeage de l’arsenic variés. L’arsenic peut précipiter sous forme de minéraux arséniés, principalement sous forme d’arséniates de calcium, mais aussi de divers autres composés secondaires variables d’une matrice à l’autre. Un piégeage physique des grains de rejets miniers arséniés par les hydrates cimentaires peut aussi avoir lieu, par formation d’un revêtement limitant l’oxydation des sulfures porteurs d’arsenic. Tous ces mécanismes interviennent dans la stabilisation/solidification de l’arsenic. / The objective of this study is to understand the geochemical behaviour of arsenic in cemented paste backfills. This technique consists in transporting the tailings in the mine openings. Two types of backfills are prepared in the laboratory for this study. First, synthetic cemented paste backfills artificially spiked with arsenic are synthesized, using silica in replacement of the tailings. In parallel, other cemented paste backfill specimens are prepared with arsenic-rich tailings. In the two cases, various types of hydraulic binders are tested. Several types of investigations are conducted on the cemented paste backfill specimens. A mineralogical characterization is carried out with the help of specific tools. At the same time, cemented paste backfill samples are submitted to several complementary leaching tests, to assess the mobility/immobilization potential of arsenic in these matrices. Finally, geochemical modeling is implemented, based on the results of the two previous studies, in order to refine the understanding of the nature and stability of the arsenic compounds. The results show that arsenic is better immobilized in Portland cement and slag-based matrices, rather than in fly ash-based matrices. The variable leaching behaviour from a given matrix to another is due to different arsenic trapping mechanisms. Arsenic can precipitate and form several arsenic minerals, mainly calcium arsenates, but also various other secondary compounds, which are different from a matrix to another. Physical entrapment of the tailings grains by the cementitious minerals can also occur, by formation of a coating around the grains, limiting the oxidation and dissolution of arsenic-bearing sulfides (passivation). These mechanisms are involved in the stabilization/solidification of arsenic by cemented paste backfills.