Foundation uplift is the partial separation of a shallow foundation from soil due to excessive load eccentricity. Foundation uplift can significantly change the seismic response of slender structures, and frames as well. In literature, different support models for foundations are employed in order to simulate foundation uplift in seismic analysis of structures. One of the most widely used models is the Winkler model which assumes distributed tensionless springs beneath a shallow foundation. In this study, two simple algorithms are developed in order to compute static and dynamic response of foundations on tensionless supports. Any formula given in literature for calculation of foundation impedance coefficients can be easily introduced in these algorithms. Hence, the use of Winkler model is critically evaluated through comparisons with the response of a foundation on elastic halfspace. For that purpose, available impedance formulas given for a shallow rectangular foundation on elastic halfspace are used. It is concluded that, the coupling between vertical displacement and rocking of foundation is very significant during uplift. Therefore, the accuracy of Winkler model in uplift v simulation is limited, since the model cannot simulate vertical and rocking response of a shallow foundation concurrently with a single spring coefficient.

Slope stability is an important aspect of geotechnical engineering. Input parameters for the analysis are the governing factors and they must be determined accurately and precisely. Field investigations, laboratory testing and back analyses are vital instruments for the input parameters. This study presents the results of slope stability analysis for the soil slopes at Elbistan-&Ccedil / &ouml / llolar lignite mine. After executing the drilling programme, samples taken from the drilling work, delivered to soil mechanics laboratory for testing. The basic input parameters, namely cohesion and friction angle determined at soil mechanics laboratory were compared to the parameters obtained from back analysis of a large scale slope failure. Input parameters for the analysis are determined by this way. After determining the input parameters, slope stability analyses were carried out both for the permanent and temporary slopes in AfSin-Elbistan lignite basin, &Ccedil / &ouml / llolar sector. The effect of ground water on the stability of slopes was investigated in detail and maximum safe slope angles were determined for different water levels. For limit equilibrium analysis, Rocscience SLIDE software, for finite difference analysis in 3-D, Itasca FLAC3D was used. In the limit equilibrium analyses both circular and composite failures were considered. Shear strength reduction method is used for the finite difference method. The results between limit equilibrium and 3-D finite difference methods were compared. When the failure surfaces obtained from the finite difference analyses were imposed to limit equilibrium analysis, computations are resulted in lower factor of safety values for limit equilibrium analysis.

ABSTRACT HYDRAULICS OPTIMIZATION OF FOAM DRILLING IN DRILLING OPERATIONS &Ouml / zer, Ceren M. Sc., Department of Petroleum and Natural Gas Engineering Supervisor: Assoc. Prof. Dr. Evren &Ouml / zbayoglu September 2009, 72 pages In drilling, drilling fluid affects every single step of operation. If rig system is thought as the human body, drilling mud can be defined as the blood system of it. Drilling fluid carries the cuttings, cools the bit, it conditions the hole and so on. Some special kinds of drilling fluids are used for special purposes such as underbalanced drilling. Underbalanced drilling is generally used to prevent formation damage, lost circulation and to increase the penetration rate.Since 1980&rsquo / s foam is used as drilling fluid for underbalanced drilling purposes and there are some models for bit hydraulic optimizations. In this study, mathematical model has been derived considering not the volumetric flow rate but the mass flow rate of the foams. Maximum hydraulic horse power at the bit is determined as a function of mass flow rate. Using this concept, optimum volumetric flow rates for liquid and gas phases as well as optimum nozzle size are determined.Using this mathematical model, a computer program is developed for comparing the results with the existing data available in the literature. It accounts for the compressibility of foam and pressure losses inside the drill string, bit and annulus.Hole size, drill-string properties, formation temperature and pressure, maximum inlet pressure are used as input parameters. Program calculates static back pressure,pressure losses in the whole system, bottom hole foam properties such as quality and velocity and optimum liquid and gas flow rates which are the key parameters of foamdrilling optimization. Results show that liquid and gas rates should be increased with increasing hole sizeand formation pressure. Increasing temperature gradient causes a minimal decrease on foam rate properties. In addition, pressure losses due to friction increases with increasing hole size and formation pressure. Decrease in formation temperature also decreases the foam quality. Changes in temperature gradient causes minimal changes on foam rate properties. Comparisons of the proposed model with other models from the literature also gave good match. The optimization criteria and assumptions are differing from the existing models. As a result the comparison does not have to one to one match with the others. The results from this study may be used for optimization of flow rate of foam as drilling fluid based on mass flow.

A parametric study is performed to investigate the parallel tunnel interaction. Three dimensional finite element analyses were performed to determine the effects of soil stiffness, pillar width and advancement level of the second tunnel on the behaviour of displacement, bending moment and shear force of the previously constructed tunnel. In the analysis PLAXIS 3D Tunnel geotechnical finite element package was used. This program allows the user to define the actual construction stages of a NATM tunnel construction. In the analysis, construction stages are defined in such a way that firstly one of the tunnels is constructed and the construction of the second tunnel starts after the construction of the first tunnel. The mid-length section of the first tunnel is investigated in six different locations and at seven different advancement levels in terms of displacement, bending moment and shear forces. It is found that, displacement and bending moment behaviour are more related with soil stiffness and pillar width than the behaviour of shear forces. While the level of advancement of the second tunnel causes different type of responses on the shear force behaviour, level of advancement does not affect the type of behaviour of displacements and bending moments. Another finding of the research is that pillar width has an evident influence on the behaviour of displacements and bending moment than the soil stiffness. It is also found that the interaction effect may be eliminated by increasing the pillar width equal or larger than an approximate value of 2.5 &ndash / 3.0 D (diameter) for an average soil stiffness value.

Drilling operation expanded through deep water environments starting from mid-1980. As water depth increased, hydrate bearing formation in the shallow ocean floor is observed and that started to cause problems during drilling and production operations. Problems due to hydrate dissociation and forming during operations are also reported by the companies working in those environments many times. Although there are several factors affect the dissociation of shallow hydrate bearing sediments, heat flux from deeper sections of the well through shallower section during the operation is the major one. In order to mitigate that risk in this study, Black Sea is taken as a reference drilling environment. Hydrate phase boundary of the region is calculated via using actual temperature and pressure data gathered during drilling operations. Generic wellbore is defined and common drilling operation sequence is simulated in this defined wellbore. Heat transfer from section target depths to the shallow wellbore section is observed during simulations. Reducing effect of low inlet temperatures and a low circulation rate on wellbore temperatures are determined. In addition positive effect of riser boosting on depressing wellbore temperature in the well head is determined. Black Sea deep water hydrate stability zone is determined between 2210-2275m. Target depth limitation for generic well designed in drilling operations is determined as 4600m.

Anisotropy in engineering properties of soils occurs due to the depositional process forming the soil fabric and/or different directional stresses in soil history. This study investigates the anisotropy in undrained shear strength and drained compressibility of preconsolidated, stiff and fissured Ankara Clay. The compressibility behavior is determined using standard oedometer testing while the shear strength anisotropy is investigated through large diameter unconsolidated-undrained triaxial testing on undisturbed samples taken in vertical and horizontal directions from several deep excavation sites along the Konya Road in &Ccedil / ukurambar-Balgat Area, Ankara. According to the results achieved, Ankara Clay is slightly anisotropic in compressibility, with an anisotropy ratio between 0.72 and 1.17 in terms of coefficient of volume compressibility for several pressure ranges between 50 kPa and 1600 kPa. On the other hand, while a slight anisotropy in undrained shear strength at a ratio ranging between 0.87 and 1.19 in terms of deviator stress can be observed in Ankara Clay, considering the great variation in the test results of samples in same direction which mostly overlaps with the range of results obtained in the other direction, it has been concluded that the Ankara Clay located in this area can be regarded as isotropic in terms of shear strength for practical purposes.

The objective of this study is to investigate the stability problems in tailing (i.e. mine waste) dams. A tailing dam is an embankment dam (made of natural borrow or tailing material) constructed to retain slurry-like mining wastes that are produced as a result of operation of mines. In the last 30 years, the stability of tailing dams has drawn much attention as a significant number of tailing dam failures have been recorded worldwide. These instability problems caused significant loss of life and damage to property in addition to environmental hazards. In this study causes of failure of tailing dams and their stability problems are investigated with respect to their geometric and material characteristics. Seepage and stability of tailing dams are studied through limit equilibrium method and finite element method. The effects of uncertainties in material properties on the stability of tailings dams is investigated. Within this context, Kastamonu-Kure copper tailings dam is used as a case study and material properties are determined by laboratory tests.

published_or_final_version / Urban Planning / Master / Master of Science in Urban Planning

published_or_final_version / Public Administration / Master / Master of Public Administration

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