Este trabalho tem como objetivo analisar a tecnologia do ciclo refrigerante misto para obtenção de gás natural liquefeito (GNL). Nessa tecnologia, o GNL é obtido por meio do seu resfriamento através de um ciclo de refrigeração, cujo fluido refrigerante é formado por uma mistura de diversos componentes. O ciclo de refrigeração é usado para resfriar a corrente de gás natural até as condições criogênicas por meio de um trocador de calor. A determinação da composição ótima dessa mistura de refrigerantes é de suma importância para a correta e eficiente operação da planta. O modelo termodinâmico para o cálculo de equilíbrio de fases dos componentes da mistura refrigerante é o baseado na Lei de Raoult, válido para misturas e soluções ideais. Inicialmente, revisam-se os conceitos de refrigerantes mistos, curvas compostas e o ponto de pinça (pinch point), utilizados na implementação da solução computacional. A aplicação dos modelos de gás e solução ideal influencia nos resultados, mas, não obstante, produz bons resultados como os obtidos no presente trabalho. A operação eficiente do ciclo depende, sobretudo, de três parâmetros principais, quais sejam: vazão da mistura refrigerante, razão de pressões alta e baixa do ciclo de refrigeração e composição da mistura refrigerante. Da análise dos resultados obtidos conclui-se que a alteração nas proporções da composição do refrigerante muda significativamente a forma das curvas composta quente e composta fria, quando comparados à alteração dos níveis de pressão e da vazão do ciclo refrigerante. Entretanto, a operacionalização do ciclo somente ocorre se um dado conjunto de valores daqueles parâmetros satisfaça uma determinada diferença mínima de temperatura, ou ponto de pinça, entre as curvas composta quente e composta fria dentro do trocador de calor. Assim, a operação eficiente do ciclo de refrigeração requer a otimização daqueles três parâmetros operacionais. / This work has the objective of analyzing the technology of mixed refrigerant cycle for obtaining liquefied natural gas (LNG). In that technology, the liquefied natural gas is obtained by means of cooling through a refrigeration cycle, whose fluid refrigerant is formed by a mixture of various components. The refrigeration cycle is used to cool the natural gas stream to cryogenic condition with the use of a heat exchanger. The determination of the optimal composition of this refrigerant mixture is very important for the correct and efficient operation of the plant. The thermodynamic model for the equilibrium phase calculation of the refrigerant mixture is based on the Law of Raoult, which is valid for ideal mixtures and solutions. Initially, the concepts of refrigerant mixture, composite curves and pinch point used in the implementation of the numerical solution were reviewed. The application of ideal-gas and ideal-solution models has influence on the results. Nevertheless, it produces good results as those obtained in the present work. The efficient operation of the cycle depends essentially of three key parameters, which are: refrigerant flow rate, the ratio of high to low pressures of the refrigerant cycle and the mixed refrigerant composition. The results indicated that the composition variation of the refrigerant changes significantly the shape of hot and cold composite curves in comparison to the modification in the pressure levels and the refrigerant flow rate of the refrigerant cycle. However, the process will operate only if a given set of values of those parameters satisfies a minimum temperature difference, or pinch point, between the hot and cold composite curves within the heat exchanger. Thus, the efficient operation of the refrigerant cycle requires the optimization of those three operational parameters.

The cryogenic carbon capture™ (CCC) process provides energy- and cost-efficient carbon capture and can be configured to provide an energy storage system using an open-loop natural gas (NG) refrigeration system, which is called energy storing cryogenic carbon capture (CCC-ES™). This investigation focuses on the transient operation and especially on the dynamic response of this energy storage system and explores its efficiency, effectiveness, design, and operation. This investigation included four tasks.The first task explores the steady-state design of four different natural gas liquefaction processes simulated by Aspen HYSYS. These processes differ from traditional LNG process in that the CCC process vaporizes the LNG and the cold vapors return through the LNG heat exchangers, exchanging sensible heat with the incoming flows. The comparisons include costs and energy performance with individually optimized processes, each operating at three operating conditions: energy storage, energy recovery, and balanced operation. The second task examines steady-state and transient models and optimization of natural gas liquefaction using Aspen HYSYS. Steady-state exergy and heat exchanger efficiency analyses characterize the performance of several potential systems. Transient analyses of the optimal steady-state model produced most of the results discussed here. The third task explores transient Aspen HYSYS modeling and optimization of two natural gas liquefaction processes and identifies the rate-limiting process components during load variations. Novel flowrate variations included in this investigation drive transient responses of all units, especially compressors and heat exchangers. Model-predictive controls (MPC) effectively manages such heat exchangers and compares favorably with results using traditional controls. The last task shows how an unprocessed natural gas (NG) pretreatment system can remove more than 90% of the CO2 from NG with CCC technology using Aspen Plus simulations and experimental data. This task shows how CCC-based technology can treat NG streams to prepare them for LNG use. Data from an experimental bench-scale apparatus verify simulation results. Simulated results on carbon (CO2) capture qualitatively and quantitatively agree with experimental results as a function of feedstock properties.

Deep foundations such as driven piles are often used to bypass liquefiable layers of soil and bear on more competent strata. When liquefaction occurs, the skin friction around the deep foundation goes to zero in the liquefiable layer. As the pore pressures dissipate, the soil settles. As the soil settles, negative skin friction develops owing to the downward movement of the soil surrounding the pile. To investigate the magnitude of the skin friction along the shaft three driven piles, an H-pile, a closed end pipe pile, and a concrete square pile, were instrumented and used to measure soil induced load at a site near Turrell, Arkansas following blast-induced liquefaction. Measurements were made of the load in the pile, the settlement of the ground and the settlement of piles in each case. Estimates of side friction and end-bearing resistance were obtained from Pile Driving Analyzer (PDA) measurements during driving and embedded O-cell type testing. The H-pile was driven to a depth of 94 feet, the pipe pile 74 feet, and the concrete square pile 72 feet below the ground surface to investigate the influence of pile depth in response to liquefaction. All three piles penetrated the liquefied layer and tipped out in denser sand. The soil surrounding the piles settled 2.5 inches for the H-pile, 2.8 inches for the pipe pile and 3.3 inches for the concrete square pile. The piles themselves settled 0.28 inches for the H-pile, 0.32 inches for the pipe pile, and 0.28 inches for the concrete square pile. During reconsolidation, the skin friction of the liquefied layer was 43% for the H-pile, 41% for the pipe pile, and 49% for the concrete square pile. Due to the magnitude of load felt in the piles from these tests the assumption of 50% skin friction developing in the liquefied zone is reasonable. Reduced side friction in the liquefied zone led to full mobilization of skin friction in the non-liquefied soil, and partial mobilization of end bearing capacity. The neutral plane, defined as the depth where the settlement of the soil equals the settlement of the pile, was outside of the liquefied zone in each scenario. The neutral plane method that uses mobilized end bearing measured during blasting to calculate settlement of the pile post liquefaction proved to be accurate for these three piles.

The study of particle morphology plays an important role in understanding the micromechanical behavior of cohesionless soil. Shear strength and liquefaction characteristics of granular soil depend on various morphological characteristics of soil grains such as their particle size, shape and surface texture. Therefore, accurate characterization and quantification of particle shape is necessary to study the effect of grain shape on mechanical behavior of granular assembly. However, the theoretical and practical developments of quantification of particle morphology and its influence on the mechanical response of granular assemblies has been very limited due to the lack of quantitative information about particle geometries, the experimental and numerical difficulties in characterizing and modeling irregular particle morphology. Motivated by the practical relevance of these challenges, this research presents a comprehensive approach to model irregular particle shape accurately both in two and three dimensions. To facilitate the research goal, a variety of natural and processed sand samples is collected from various locations around the world. A series of experimental and analytical studies are performed following the sample collection effort to characterize and quantify particle shapes of various sand samples by using Fourier shape descriptors. As part of the particle shape quantification and modeling, a methodology is developed to determine an optimum sample size for each sand sample used in the analysis. Recently, Discrete Element Method (DEM) has gained attention to model irregular particle morphology in two and three dimensions. In order to generate and reconstruct particle assemblies of highly irregular geometric shapes of a particular sand sample in the DEM environment, the relationship between grain size and shape is explored and no relationship is found between grain size and shape for the sand samples analyzed. A skeletonization algorithm is developed in this study in order to automate the Overlapping Discrete Element Cluster (ODEC) technique for modeling irregular particle shape in two and three dimensions. Finally, the two-dimensional and three-dimensional particle shapes are implemented within discrete element modeling software, PFC2D and PFC3D, to evaluate the influence of grain shape on shear strength behavior of granular soil by using discrete simulation of direct shear test.

[Formulae and special characters can not be reproduced here. Please see the pdf version of the Abstract for an accurate reproduction.] The thesis provides a comprehensive study on the behaviour of sand with a small amount of fines [i.e.1/3 plastic fines and 2/3 non-plastic fines]. The work is carried out experimentally under axi-symmetric conditions using the triaxial apparatus. Conventional drained triaxial tests are conducted on isotropic consolidated specimens and all the tests indicate that sand with fines does not manifest any unusual behaviour under drained conditions. However in undrained shearing the so-called ???reverse behaviour??? is noted. The study demonstrates that the reverse behaviour conforms to the critical state framework because significant changes in the position and geometry of the critical state [CS] and isotropic consolidation [IL] lines are caused by the presence of fines. These changes cannot be adequately modelled by the intergranular void ratio as proposed by Thevanayagam and Mohan (2000). This study also demonstrates that the original state parameter [special character] as proposed by Been and Jefferies (1985) is not an adequate parameter to predict the undrained behaviour trend. A new parameter termed ???modified state parameter??? [special character] is proposed to account for the combined effects of density and confining pressure. The suitability of the modified state parameter to characterise the response of parent sand and sand with fines is assessed for a range of void ratios and confining pressures. The effect of drained stress history is an important factor affecting the subsequent undrained response. Drained pre-shearing to failure is found to improve considerably the subsequent undrained response to the extent that liquefaction may not occur. Different drained pre-shearing histories have different effects on the undrained response. However in these tests [special character] has limitations in quantifying the subsequent undrained stress-strain response. Hence, a new framework of ???yielding parameter??? [special character] extends the capability of [special character] and additional data is presented to demonstrate the suitability of this concept. The implementation of [special character] depends on whether the previous stress state reached during the stress history is below or at failure. The effects of drained pre-shearing on the position and movement of failure surface are investigated. It is found that drained pre-shearing to failure at larger confining pressures has the effect of shifting upwards part of the drained failure surface. The shift at larger stress ratios [special character] may be described in terms of dilatancy and modified state parameter at failure. The so-called strain path tests are conducted to study the influence of strain increment ratio on the deformation behaviour of sand with fines. It is found that the value of [special character] has significant effects on the stress-strain behaviour. Along negative [special character] paths the soil strain softens in the form of decreasing the shear resistance before reaching the failure state. In contrast, along positive [special character] paths the soil strain hardens to an asymptotic stress ratio. The asymptotic stress ratio decreases with increasing [special character] along a linear relationship. The framework of [special character] cannot quantify the stress-strain response along positive and negative strain paths. Consequently an ???instability parameter??? [special character] is proposed to extend the capabilities of [special character] and the reliability of this parameter is further assessed. The behaviour along a range of positive and negative [special character] paths is investigated on pre-sheared specimens. In negative [special character] the effective stress paths reach a surface located higher than the monotonic failure surface on which they trace downward towards the origin of stress space. The results indicate this surface may be the same as the drained failure envelope which has been shifted as a result of drained pre-shearing. In positive [special character] paths a large improvement is noted in both the strength and stiffness of the soil. Note The parameters [special character] and [special character] are all generalisations of [special character] so that the behaviour under complex conditions can be characterised.

Enhanced Integration of Shear Wave Velocity Profiling in Direct-Push Site Characterization Systems Alexander V. McGillivray 370 Pages Directed by Dr. Paul W. Mayne Shear wave velocity (VS) is a fundamental property of soils directly related to the shear stiffness at small-strains. Therefore, VS should be a routine measurement made during everyday site characterization. There are several lab and field methods for measuring VS, but the seismic piezocone penetration test (SCPTu) and the seismic dilatometer test (SDMT) are the most efficient means for profiling the small-strain stiffness in addition to evaluating large-strain strength, as well as providing evaluations of the geostratigraphy, stress state, and permeability, all within a single sounding. Although the CPT and DMT have been in use for over three decades in the USA, they are only recently becoming commonplace on small-, medium-, and large-size projects as more organizations begin to realize their benefits. Regrettably, the SCPTu and the SDMT are lagging slightly behind their non-seismic counterparts in popularity, in part because the geophysics component of the tests has not been updated during the 25 years since the tests were envisioned. The VS measurement component is inefficient and not cost effective for routine use. The purpose of this research is to remove the barriers to seismic testing during direct-push site characterization with SCPTu and SDMT. A continuous-push seismic system has been developed to improve the integration of VS measurements with SCPTu and SDMT, allowing VS to be measured during penetration without stopping the progress of the probe. A new type of portable automated seismic source, given the name RotoSeis, was created to generate repeated hammer strikes at regularly spaced time intervals. A true-interval biaxial seismic probe and an automated data acquisition system were also developed to capture the shear waves. By not limiting VS measurement to pauses in penetration during rod breaks, it is possible to make overlapping VS interval measurements. This new method, termed frequent-interval, increases the depth resolution of the VS profile to be more compatible with the depth intervals of the near-continuous non-seismic measurements of the SCPTu and the SDMT.

Although there exist some consensus regarding seismic soil liquefaction assessment of free field soil sites, estimating the liquefaction triggering potential beneath building foundations still stays as a controversial and difficult issue. Assessing liquefaction triggering potential under building foundations requires the estimation of cyclic and static stress state of the soil medium. For the purpose of assessing the effects of the presence of a structure three-dimensional, finite difference-based total stress analyses were performed for generic soil, structure and earthquake combinations. A simplified procedure was proposed which would produce unbiased estimates of the representative and maximum soil-structure-earthquake-induced iv cyclic stress ratio (CSRSSEI) values, eliminating the need to perform 3-D dynamic response assessment of soil and structure systems for conventional projects. Consistent with the available literature, the descriptive (input) parameters of the proposed model were selected as soil-to-structure stiffness ratio, spectral acceleration ratio (SA/PGA) and aspect ratio of the building. The model coefficients were estimated through maximum likelihood methodology which was used to produce an unbiased match with the predictions of 3-D analyses and proposed simplified procedure. Although a satisfactory fit was achieved among the CSR estimations by numerical seismic response analysis results and the proposed simplified procedure, validation of the proposed simplified procedure further with available laboratory shaking table and centrifuge tests and well-documented field case histories was preferred. The proposed simplified procedure was shown to capture almost all of the behavioral trends and most of the amplitudes. As the concluding remark, contrary to general conclusions of Rollins and Seed (1990), and partially consistent with the observations of Finn and Yodengrakumar (1987), Liu and Dobry (1997) and Mylonakis and Gazetas, (2000), it is proven that soil-structure interaction does not always beneficially affect the liquefaction triggering potential of foundation soils and the proposed simplified model conveniently captures when it is critical.

The purpose of this study is to develop a geotechnical microzonation model regarding the suitability of the residential areas in Yenisehir (Bursa, Turkey), which is a currently developing settlement area in a seismically active region. For this purpose, soil properties and dynamic soil behaviors of the study area were assessed. Soil classification, soil amplification, natural soil predominant period, resonance phenomena and liquefaction potential of the study area were evaluated using borehole data and microtremor measurements. The raw data obtained from the previous studies carried out at Yenisehir were used for these assessments. The liquefaction potential for the study area was evaluated both in two-dimensional planimetric and three-dimensional volumetric assessments. Two geotechnical microzonation maps were produced for the study area according to the surface damage due to liquefaction (according to two different methods), soil amplification and distance to streams maps / by using Geographical Information Systems (GIS) based Multi-Criteria Decision Analysis. The weight values were assigned to the layers using Analytical Hierarchical Process method by pairwise comparisons. Evaluating geotechnical microzonation maps produced, the safest areas were found on the northern sites of the study area. The most critical areas were found to be in the middle and the southeast parts of the study area.

Based upon the upper bound limit analysis, the stability numbers have been developed for a two-layered soil slope both for an associated flow rule material and for a homogeneous slope with non-associated flow rule material. The failure surface was assumed to be an arc of logarithmic spiral and it automatically ensures the kinematics admissibility of the failure mechanism with respect to the rigid rotation of the soil mass about the focus of the logarithmic spiral. The effect of the pore water pressure and horizontal earthquake body forces was also included m the analysis. For a non-associated flow rule material, the stress distribution along the failure surface was developed with the assumption of interslice forces given by Fellenius and Bishop. The stability numbers have been found to reduce appreciably with increases m the (i) horizontal inclination (β) of slope, (ii) pore water pressure coefficient, ru and (iii) horizontal earthquake acceleration coefficient (kh). The values of the stability numbers for a non-associated co-axial flow rule, with dilatancy angle ψ =0, have been found to be considerably lower as compared to the associated flow rule material. For a given height of the slope, with associated flow rule, the values of the stability numbers have been found to increase with increase in the thickness of a layer with greater value of the friction angle Φ. The results have been given in the form of non-dimensional stability charts, which can be used for readily obtaining either the value of the critical height or the factor of safety The methodology can be easily extended even for multi-layered soil slopes with different values of cohesion (c), bulk unit weight (γ) and friction angle (Φ). An attempt has also been made in this thesis to study experimentally the effect of the frequency of the excitation and the addition of non-plastic fines on the liquefaction resistance of the material Shake table studies, generating uni-axial sinusoidal horizontal vibrations, were earned out for this purpose. During the period of excitation of the material, the settlement at the surface of the sample increases continuously with time up to a certain peak value and thereafter, it becomes almost constant. For the excitation of the material with higher frequency, more number of cycles was seen to reach the final settlement. With the continuous excitation of the material, the magnitude of the pore water pressures increases up to a certain peak value and there after, its magnitude decreases till it again becomes the hydrostatic pressure as it was before the excitation of the material. The peak magnitude of the pore water pressure tends to be higher for the excitation with smaller frequency especially at greater depths from the ground surface. The addition of non-plastic fines tends to increase the magnitude of the settlement as well as the increase in the pore water pressure.

As a consequence of the 2010 – 2011 Canterbury earthquake sequence, Christchurch experienced widespread liquefaction, vertical settlement and lateral spreading. These geological processes caused extensive damage to both housing and infrastructure, and increased the need for geotechnical investigation substantially. Cone Penetration Testing (CPT) has become the most common method for liquefaction assessment in Christchurch, and issues have been identified with the soil behaviour type, liquefaction potential and vertical settlement estimates, particularly in the north-western suburbs of Christchurch where soils consist mostly of silts, clayey silts and silty clays. The CPT soil behaviour type often appears to over-estimate the fines content within a soil, while the liquefaction potential and vertical settlement are often calculated higher than those measured after the Canterbury earthquake sequence. To investigate these issues, laboratory work was carried out on three adjacent CPT/borehole pairs from the Groynes Park subdivision in northern Christchurch. Boreholes were logged according to NZGS standards, separated into stratigraphic layers, and laboratory tests were conducted on representative samples. Comparison of these results with the CPT soil behaviour types provided valuable information, where 62% of soils on average were specified by the CPT at the Groynes Park subdivision as finer than what was actually present, 20% of soils on average were specified as coarser than what was actually present, and only 18% of soils on average were correctly classified by the CPT. Hence the CPT soil behaviour type is not accurately describing the stratigraphic profile at the Groynes Park subdivision, and it is understood that this is also the case in much of northwest Christchurch where similar soils are found. The computer software CLiq, by GeoLogismiki, uses assessment parameter constants which are able to be adjusted with each CPT file, in an attempt to make each more accurate. These parameter changes can in some cases substantially alter the results for liquefaction analysis. The sensitivity of the overall assessment method, raising and lowering the water table, lowering the soil behaviour type index, Ic, liquefaction cutoff value, the layer detection option, and the weighting factor option, were analysed by comparison with a set of ‘base settings’. The investigation confirmed that liquefaction analysis results can be very sensitive to the parameters selected, and demonstrated the dependency of the soil behaviour type on the soil behaviour type index, as the tested assessment parameters made very little to no changes to the soil behaviour type plots. The soil behaviour type index, Ic, developed by Robertson and Wride (1998) has been used to define a soil’s behaviour type, which is defined according to a set of numerical boundaries. In addition to this, the liquefaction cutoff point is defined as Ic > 2.6, whereby it is assumed that any soils with an Ic value above this will not liquefy due to clay-like tendencies (Robertson and Wride, 1998). The method has been identified in this thesis as being potentially unsuitable for some areas of Christchurch as it was developed for mostly sandy soils. An alternative methodology involving adjustment of the Robertson and Wride (1998) soil behaviour type boundaries is proposed as follows:  Ic < 1.31 – Gravelly sand to dense sand  1.31 < Ic < 1.90 – Sands: clean sand to silty sand  1.90 < Ic < 2.50 – Sand mixtures: silty sand to sandy silt  2.50 < Ic < 3.20 – Silt mixtures: clayey silt to silty clay  3.20 < Ic < 3.60 – Clays: silty clay to clay  Ic > 3.60 – Organics soils: peats. When the soil behaviour type boundary changes were applied to 15 test sites throughout Christchurch, 67% showed an improved change of soil behaviour type, while the remaining 33% remained unchanged, because they consisted almost entirely of sand. Within these boundary changes, the liquefaction cutoff point was moved from Ic > 2.6 to Ic > 2.5 and altered the liquefaction potential and vertical settlement to more realistic ii values. This confirmed that the overall soil behaviour type boundary changes appear to solve both the soil behaviour type issues and reduce the overestimation of liquefaction potential and vertical settlement. This thesis acts as a starting point towards researching the issues discussed. In particular, future work which would be useful includes investigation of the CLiq assessment parameter adjustments, and those which would be most suitable for use in clay-rich soils such as those in Christchurch. In particular consideration of how the water table can be better assessed when perched layers of water exist, with the limitation that only one elevation can be entered into CLiq. Additionally, a useful investigation would be a comparison of the known liquefaction and settlements from the Canterbury earthquake sequence with the liquefaction and settlement potentials calculated in CLiq for equivalent shaking conditions. This would enable the difference between the two to be accurately defined, and a suitable adjustment applied. Finally, inconsistencies between the Laser-Sizer and Hydrometer should be investigated, as the Laser-Sizer under-estimated the fines content by up to one third of the Hydrometer values.