This thesis investigates the stability of coal pillars under realistic conditions of varying weak floor thickness with and without the use of paste backfill. Weak floor strata underlying coal seams are common in the Illinois Basin. They consist mainly of underclay, which is a gray, argillaceous rock that usually occurs immediately beneath beds of coal. Underclay thickness may vary from less than a foot to twenty feet at different locations in the basin (Grim and Allen, 1938). Locally, underclay thickness may vary gradationally over a distance of two pillars. Even though weak floor thickness is not consistent (Gadde, 2009), most research to date has focused on parametric studies with a fixed underclay thickness and formulated coal pillar designs on the basis of the maximum underclay thickness measured in the field. Therefore, it is necessary to investigate more realistic field conditions and quantify the influence of a gradated weak floor thickness using additional parametric studies. This research is primarily numerical modeling incorporating various constitutive models and using some calibration. Therefore, the two dimensional plane strain finite difference model in FLAC 3D is employed to carry out parametric studies on gradated weak floor conditions. Underclay exhibits Mohr Coulomb elastic plastic behavior; hence, the Mohr Coulomb constitutive model is used for the behavior of overburden, coal, and floor. Well-calibrated numerical models can assist in understanding load and failure processes provided that coal, overburden, and weak floor are modeled with sufficient realism. The theoretical approach considers a friction angle of 0° to calculate the load bearing capacity of the weak floor for design of pillars with long-term stability, even if the weak floor has a non-zero friction angle. The stiffness of the weak floor increases with an increase in friction angle (Gadde, 2009; Kostecki and Spearing, 2015). As stiffness increases, a point can be reached where floor bearing capacity exceeds coal pillar strength and coal pillar strength becomes the governing factor. For this scenario, the Mohr Coulomb strain softening model is more realistic in estimating loads carried by coal pillars in the post-failure stage. The three-dimensional Mohr Coulomb strain softening model in FLAC 3D is employed to study qualitatively the floor response in strain softening coal behavior conditions. Maintaining stable coal pillar responses has been a challenge for the coal mining industry due to attempts to increase the primary extraction ratio. Presently, the best available solution seems to be backfilling when considering short-term pillar stability (i.e., less than the long-term factor of safety) with increased extraction ratio. There are various types of mine backfill that have benefits to the mining industry depending on the application, but paste backfill produced from total mill tailings containing no free water is the best option for post-mining ground control in room-and-pillar mines as it prevents weakening of the floor and will not contaminate the ground water. The influence of paste backfill on floor bearing capacity and coal pillar response is studied with numerical modeling using the same constitutive models already identified. Finally, an economic analysis is carried out to look at cost implications of a proposed system with backfill.

Submitted by Israel Vieira Neto (israel.vieiraneto@ufpe.br) on 2015-03-04T17:54:03Z No. of bitstreams: 2 DISSERTAÇÃO Oscar Bezerra Pezo.pdf: 5982903 bytes, checksum: b9759670a74301d6ab644f498ad40ad1 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-04T17:54:03Z (GMT). No. of bitstreams: 2 DISSERTAÇÃO Oscar Bezerra Pezo.pdf: 5982903 bytes, checksum: b9759670a74301d6ab644f498ad40ad1 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2013-07-02 / CAPES / A presente dissertação analisa, em termos do comportamento carga-recalque, um banco de dados organizado por Wilson Cartaxo Soares (2011), de fundações em grupo de estacas e radier estaqueados, executados em solo arenoso de várias camadas da área litorânea de João Pessoa/PB, com 07 provas de carga, estáticas, em estacas do tipo Hollow Auger, construídas em escala real, com 300 mm de diâmetro e 4,5 m de comprimento. Os dados foram retroanalisados com o Método dos Elementos Finitos (MEF 3D), utilizando o programa CESAR-LCPC v4 (Cleo 3D versão 1.07). Na modelagem do comportamento tensão-deformação do solo foi utilizado o modelo constitutivo de Mohr-Coulomb. Os parâmetros geotécnicos iniciais utilizados em cada um desses modelos foram obtidos através de correlações a partir de valores de NSPT obtidos por SOARES (2011). Os resultados dessas simulações numéricas foram comparados com os resultados experimentais, medidos nas provas de carga. Definiu-se os parâmetros geotécnicos do solo a partir da retroanálise por meio da modelagem numérica para serem empregados em futuras simulações no maciço. Análises paramétricas são executadas com o intuito de obter um maior conhecimento do comportamento da fundação em radier estaqueado, usando o modelo elásticoplástico de Mohr-Coulomb. Isso ocorre mediante algumas alterações de sua configuração que inclui a espessura do radier, número, diâmetro, espaçamento e comprimento das estacas embutido no solo. Carga vertical central está sendo considerada para a análise paramétrica. O recalque máximo, recalque diferencial e distorção angular do radier diminuem, com o aumento da espessura do radier, do número, comprimento e diâmetro das estacas.

Die onbevredigende konsep van die interne wrywingskoeffisient wat as basis dien vir numeries-bruikbare fraktuurkriteria vir brosmateriale, onder andere die van Coulomb-Mohr, impliseer dat daar meriete in die kriteria bestaan, maar dat daar ook fundamentele aspekte van die fraktuur.meganika vir brosmateriale bestaan wat nog ontsluit moet word. Met hierdie as onderliggende behoefte, word die probleem geidentifiseer deur eers die waarskynlike tekortkominge in die interpretasie van die bestaande teoriee in oenskou te neem. So word byvoorbeeld die rol van die inter.mediere hoofnormaalspanning met behulp van die stereografiese projeksiemetode geillustreer waaruit afgelei kan word dat die probleem, in teenstelling met die opinie van sommige ander navorsers, wel drie-dimensioneel van aard is. Daar word oak aangetoon dat die gemiddelde normaalspanningsvlak meganistiese eienskappe bevat wat daarop dui dat dit die kritieke fraktuurvlak kan wees. Aangesien hierdie vlak egter invariant ten opsigte van die normaalspanningsverwysingsnetwerk is, word die begrip netto-normaalspanning ingevoer wat 'n funksie van die Poissonverhouding is. Deur 'n funksionele verwantskap af te lei vir die helling van die Mohrenvelop wat die Mohrsirkel raak by die punt wat verteenwoordig word deur die gemiddelde netto-hoofnor. maalspanning in terme van die normaalspannings en die Poissionverhouding, word 'n moontlike materiaal-afhanklike verklaring van die interne wrywingskoeffisient verkry. Dit word bevind dat hierdie vergelyking sinvolle waardes van die interne wrywingskoeffisient voorspel, wat impliseer dat daar meriete in die benaderingswyse bestaan wat die formulering van die verwantskap voorafgegaan het. 'n Uitvloeisel van die benaderingswyse is dat dit aanleiding gee tot 'n gewysigde vorm van voorstelling van eksperimentele data. Daar word bevind dat die gewysigde voorstelling baie gevoelig is vir sekere veranderlikes en die rol van invariante toestande word ook deur hierdie voorstelling beklemtoon. 'n Afleiding wat uit hierdie verhandeling gemaak kan word, is dat dit moontlik behoort te wees om 'n fraktuurkriterium in terme van elastisiteitskonstantes te formuleer. / Dissertation (MSc)--University of Pretoria, 1976. / gm2014 / Mechanical and Aeronautical Engineering / Unrestricted

>Magister Scientiae - MSc / The Keimoes Suite is a group of poorly defined granitoids that characterize the Namaqua Front and Foreland zones. There is a lack of knowledge on its content and distribution. A significant amount of work has been done on the geochemical and geochronological aspects of the Keimoes Suite but no structural analysis using a comparison between joint occurrences in the suite and the country rock has been found in the literature. This study provides insight on whether these joints formed as a result of the emplacement and subsequent cooling of the granitoids or whether they are the result of later deformation processes. This was achieved through remote sensing, detailed field mapping and structural analysis of joint data to determine the type of stress regime associated with their deformation. Eleven granitoids of the Keimoes Suite were mapped in the Kakamas-Keimoes area in the Northern Cape, South Africa. Up to four joint sets were mapped and characterized according to orientation, abutting relationship, in-filling material and spacing properties. The orientation analysis revealed two prominent joint sets (NNW and NE) that are consistent throughout the Keimoes Suite granite. However after careful analysis of their abutting relationship it has been concluded that these joints are the youngest joints formed in the Keimoes Suite. The fourth set is the E-W set which does not occur at a wide spread scale. The oldest joint set (NNE) is defined by the quartz and feldspar filling and these joints only occur in the oldest granite of the suite. Field observation revealed shear displacement, forming a conjugate joint set. This conjugate set closes at an acute angle of 60˚ and the joints displace each other. The presence of en echelon sigmoidal veins suggests these joints formed as mode II fractures and that they are tectonic joints. The dominant joint set NNW is parallel to the regional foliation, shear zones and faults which were formed during the D2 deformational vent of the Namaqua Orogeny. This NNW joint set post-dates the D2 deformational event and was formed during the D3 deformational environment of the Namaqua Orogeny. Principal stress analysis of all the joints in the study area suggests a strike-slip environment, which coincides with the D3 deformation event of the Namaqua Natal Province. Even though the country rock and the Keimoes Suite granites were subjected to same stress field during the D3 event, the analysis of principal stresses between the Keimoes Suite granites and the country rock reveals a slight difference in the orientation of the principal stresses. This is caused by the difference in competency between the Keimoes Suite granites and the country rock thus caused the refraction. In conclusion Structural evidence on various members of the Keimoes Suite indicates three episodes of intrusions with respect to the D2 Namaqua deformation event based on foliation and mineral filled joints. The Vaalputs Granite is pre tectonic relative to the main D2 deformation event and the thermal peak M2 metamorphisms, while Louisvale, Kanon Eiland and Klip Kraal Granites are syn-tectonic to these deformation events. The granites that lack foliation are classified as post-tectonic granites and these are the Keboes, Kleinbegin, Gemsbokbult, Colstone and Cnydas Granites as well as the Friesdale Charnockite. However the presence of foliation in some granites suggests that a compressional episode existed for a period of time and ended sometime before the onset of the post-tectonic granites. Therefore the D2 pre-dates the last episode of Keimoes Suite granite emplacement. This study partly validates the work done by previous workers on the Keimoes Suite, although there are some slight differences which are subjected to change. Conclusion can be drawn that this study provided additional insight in the findings of other workers nonetheless also differs with some of their findings regarding the timing of emplacement of the Keimoes Suite.

A nonlinear Mohr-Coulomb constitutive model with a strain dependent yield surface and non-associated flow was employed to study the plastic soil properties which affect the rate of surface fault rupture propagation in reverse events. These numerical simulations show a trend for soils with higher stiffness to have a higher rate of rupture propagation. Additionally the study shows the effects of strain softening and hardening on the rate of rupture propagation. Soils which strain harden exhibiting ductile behavior typically require more basal offset to rupture to the surface than soils which strain soften exhibiting brittle behavior. These results agree with our previous fault box studies, which showed that soils with higher near surface shear wave velocity were more likely to propagate rupture to the surface for a given reverse event. The numerical modeling allowed for a more comprehensive evaluation of material types and fault angles than the fault box, and provided confidence in these findings.

Railways are one of the largest transportation networks in the world that play an important role in the mass transportation of both the passengers and freight. The speed of trains and as well as the axial load carrying capacity have been increasing significantly during the past few decades to keep in pace with the population and economy growth and to compete with other modes of transportation such as the road, air and water transportation system. Billions of dollars are spent annually for maintenance of rail tracks in the world. The efficient and optimum use of these funds is a challenging task that demands innovative and cutting edge technologies in railway engineering. The railway subgrade is an important part of railway foundation and should be capable of providing a suitable base supporting the ballast and subballast to accommodate the stresses due to traffic loads without failure or excessive deformation. The progressive shear failure is a well-known and age old challenging problem for railways over the world for centuries. The subgrade of railway track which typically constitutes of fine-grained material tends to fail through the accumulation of soil movements up- and sideward developing a path for the least resistance along which progressive shear failure occurs under repeated train-induced loads and due to the effects of climate factors. To-date, limited number of studies have addressed failure mechanism associated with the progressive shear failure, especially using the mechanics of unsaturated soils. In this thesis, a novel and first of its kind, Visual Basic program developed in AutoCAD environment based on Mohr-Coulomb failure criteria and unsaturated soil mechanics theory. This program is capable of taking account of the influence of matric suction and simulate progressive shear failure in the subgrade under moving train. Simulation results suggest several parameters that include stress distribution, matric suction, cohesion, coefficient of lateral earth pressure at rest, and coefficient of residual friction as well as the angle of internal friction have a significant effect on the progressive shear failure and the shape of failure planes in the subgrade. The progressive shear failure in subgrade can be reduced by increasing matric suction, cohesion, coefficient of lateral earth pressure at rest, and coefficient of residual friction as well as the angle of internal friction, and optimizing combination of these parameters. The simulation results suggest the progressive shear failure can be well simulated with the Mohr-Coulomb failure criteria. Several suggestions are made for railway subgrade construction and maintenance based on the results of this study.

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.

Latina women have been made to believe that their lives and desires are always secondary to the needs of men and children. As a result, many women have developed a martyr complex wherein the measure of their value is how much suffering they can endure in service to their family. There is subsequently a culture of self-sacrifice best exemplified by the archetype known as "la sufrida." This thesis explores the sufrida role in literature while using the history of the author's mother—a woman whose life can be "read" as that of a real sufrida— as a bridge between literature and reality. This thesis discusses works of prominent Latinx and Caribbean women writers such as Judith Ortiz Cofer and Nicholasa Mohr and further analyzes the social and religious constraints that instill self-sacrificial mentalities in women. Through the use of womanist and cultural criticisms, this thesis highlights the complex social paradigms that cause so many Latinas to internalize self-limiting thinking patterns. The author's goal is to expose the sufrida role as valueless for contemporary women.

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An improved equation is presented for the prediction of the ultimate strength of the local zone in Load Transfer Tests. The derivation of this new formulation is the result of the investigation of the ultimate bearing strength of plain and reinforced concrete blocks, concentrically loaded. A total of 199 bearing tests were performed on plain and reinforced concrete prisms to evaluate the variables involved in the bearing problem. A finite element analysis of a typical square block loaded with different bearing areas was performed. Two equations, one for plain concrete and the other for reinforced concrete were derived using the Mohr failure criterion. The performance of the derived equations was evaluated against actual test data. The results of this evaluation showed very good agreement between the predicted ultimate strength and the actual test strength for both plain and reinforced concrete. For plain concrete specimens the ratio Ptest/Ppred was 1.05 with a coefficient of variation of 9 percent. In the case of reinforced concrete blocks the ratio Ptest/Ppred was 1.00 with a coefficient of variation of 14 percent. / Master of Science