This study has investigated thresholds of damage for privately owned low-rise residential properties damaged by ground subsidence or heave movement. The primary focus of the research objectives has been the uncertainties created by subsidence damage. The study investigates thresholds of damage that can be used to assess the remedial action necessary for low-rise residential properties damaged by ground subsidence or heave movement. After investigating thresholds of damage, the study subsequently considers the implications that thresholds of damage would create if applied in practice. The research was carried out through the collection and analysis of 236 case study properties. Each case study represents a privately owned low-rise residential property that was thought to have been damaged by ground subsidence or heave movement. The research has considered properties damaged by subsidence or heave movement caused by leaking drains, clay subsoil shrinkage or expansion and subsidence caused by coal-mining. Case study information has been gathered from a variety of sources, using data collected by professionally qualified chartered engineers, surveyors or other specialists. In addition to these case studies, the research has employed semi-structured interviews in order to consider the implications that thresholds of damage would create if applied in practice. The research found that the evaluation of visible damage is a highly subjective matter and that any thresholds based upon an assessment of visible damage are an unreliable method to consider whether or not a property requires substantive repairs. The most robust threshold of damage which is found to emerge was to evaluate whether or not the movement causing the damage in the property is long-term progressive. The consequences of implementing this threshold of damage have been investigated. It has been concluded that if this threshold of damage was adopted, it could lead to both reductions in payments necessary to repair subsidence or heave damage and it could also reduce some of the uncertainties associated with subsidence.

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2014. / Submitted by Ana Cristina Barbosa da Silva (annabds@hotmail.com) on 2015-06-24T14:33:01Z No. of bitstreams: 1 2014_WilliamHumbertoCuellarSanchez.pdf: 2631076 bytes, checksum: a3ae151514ca63aa4c29c5d9d1474193 (MD5) / Approved for entry into archive by Raquel Viana(raquelviana@bce.unb.br) on 2015-06-24T15:03:23Z (GMT) No. of bitstreams: 1 2014_WilliamHumbertoCuellarSanchez.pdf: 2631076 bytes, checksum: a3ae151514ca63aa4c29c5d9d1474193 (MD5) / Made available in DSpace on 2015-06-24T15:03:23Z (GMT). No. of bitstreams: 1 2014_WilliamHumbertoCuellarSanchez.pdf: 2631076 bytes, checksum: a3ae151514ca63aa4c29c5d9d1474193 (MD5) / Durante a perfuração de um poço offshore, o bloco de coroamento e a coluna de perfuração são suportados por um compensador, este impedindo que o movimento da plataforma gerado pelas ondas seja transmitido ao bloco de coroamento. Se o compensador não for eficiente, o movimento do bloco de coroamento é transferido à coluna de perfuração, gerando variações de carga sobre a broca, pistoneio e flambagem da coluna de perfuração. Estes problemas podem danificar a broca, a coluna de perfuração, as paredes do poço e causar um influxo dos fluidos do reservatório para o poço. Assim, a perfuração deve ser interrompida para evitar o risco de acidentes graves, perdendose tempo de operação e dinheiro. Por isso, um sistema compensador para atenuar as vibrações transmitidas pela plataforma ao bloco de coroamento é de extrema importância. Este documento mostra como foi projetado o sistema compensador de heave (movimento de afundamento) para um processo de perfuração offshore de 6 km de profundidade e apresenta o controle semiativo. O compensador é projetado com duas configurações de suspensão hidropneum ática, a primeira é uma suspensão hidropneumática simples e a segunda é uma suspensão hidropneumática simples em série com uma mola mecânica. A modelagem foi feita para cada sistema de suspensão e encontrou-se a respectiva função de transferência. Os polos dessas funções de transferência foram projetados para terem os mesmos polos sugeridos para um filtro Butterworth passa-baixas de segunda e terceira ordem. O objetivo deste controle semiativo é manter um desempenho aceitável do compensador quando a massa da coluna de perfuração é modificada, pois essa mudança afeta o comportamento do sistema de suspensão hidropneumático. A ação de controle é executada apenas por uma válvula servo comandada e esta ação modifica o valor do amortecimento do sistema e, assim, o comportamento do compensador é mantido um nível aceitável. Esta válvula é a única parte móvel do sistema de controle e, portanto, este sistema é mais robusto em relação às falhas mecânicas ou elétricas e possui um baixo consumo de energia. Os resultados são obtidos com uma simulação feita em MATLAB. As respostas em frequência mostram melhores resultados quando é usado o controle semiativo para o compensador de heave que foi projetado com a suspensão hidropneumática simples, quando a massa da coluna de perfuração for alterada, este compensador pode funcionar sem sistemas ativos obtendo um comportamento aceitável. Com base na simulação, verifcou-se que o compensador projetado com a suspensão hidropneumática simples em série com uma mola mecânica não é realizável ao aplicar a metodologia proposta nesta dissertação. ____________________________________________________________________________________ ABSTRACT / During the drilling of an offshore well, the crown block and the drill string are supported by a compensator, which prevents movement of the crown block, due to the platform heave. Without an eficient compensator, the displacement of the drill string can generate load variations on the drill bit, swabbing, and buckling of the drill string. These problems can generate drill bit damage, drill string damage, collapse of the borehole wall and well kick. If the compensator is not able to satisfactorily compensate the heave, the drilling is stopped to avoid the risk of major accidents. Stopping the drilling causes loss of operation time and money. Thus, a compensator system, which mitigates the vibrations transmitted by the platform to the crown block, is of utmost importance. This work shows the designing of a heave compensation system and a semi-active control according to the requirements drilling 6km deep offshore. Two approaches for compensator design are studied, the first is the basic hydropneumatic suspension and the second is the basic hydropneumatic suspension in series with the mechanical spring. The modelling of each suspension was made to find the transfer function and the poles of compensator transfer function were designed to have the suggested pole by the Butterworth filter low-pass. The goal of this semi-active control is to maintain an acceptable performance of the system when the drill string mass changes, which also changes the performance of the hydropneumatic system. The control action is executed just by a servo valve, which modifies the system damping to optimize the compensator performance. This servo valve is the only moving part of the control system and therefore, this system is more robust regarding mechanical/ electrical failures and it has low consumption energy. The results show a better and satisfactory frequency response of semi-active control for heave compensator that was designed with the basic hydropneumatic suspension, when the drill string mass is changed, this compensator can work without active systems. The designed compensator with the basic hydropneumatic suspension in series with the spring was not feasible with the applied methodology.

Frost heave is the expansion of soil upon freezing due to the formation and growth of segregated ice lenses. Because of the large stresses and displacements associated with frost heave, it is an import design consideration for geotechnical structures such as roads, foundations, and buried pipelines, particularly in cold regions. The objective of this research was to characterize frost heave expansion within the context of design and analysis applications. A series of laboratory-scale frost heave experiments were conducted to examine frost heave under one-dimensional freezing. The previously established segregation potential concept (SP) was utilized to characterize both the intrinsic frost heave behavior of two reference soils. A novel modification was proposed to account for the observed variation of SP with freezing rate; it was noted that ignoring this influence would lead under-predictions the heave expansion. The thermal properties of frozen soils were explored. A method for characterizing the anisotropic thermal conductivity was proposed utilizing existing composite models in a multi-level homogenization. Ultimately it was determined that for ice lens-rich soils, a simpler and isotropic expression may provide similar performance, namely the geometric mean approximation. Additionally, a method was proposed to characterize the thermal conductivity of composite materials containing discrete particle phases using numerical simulations of complex phase geometries. This method was used to develop a specified characterization of discrete particle composites. iv A two-dimensional, fully coupled thermal-mechanical and implicitly coupled hydraulic frost heave model was formulated from thermodynamic principles. The model included the proposed form of SP to characterize the mass transport process. The finite element method was used to implement the model and its performance was validated in one-dimension through comparative analysis with the laboratory frost heave tests. Finally, the model was applied to a two-dimensional, full-scale problem involving the frost heave- induced displacement of a chilled natural gas problem. / Thesis / Doctor of Philosophy (PhD) / An experimental investigation was conducted and a numerical model was developed to predict the effects of frost heave in freezing soils. Frost heave is the expansion of soils caused by the formation of a specific type of ice, called ice lenses. This expansion can cause damage and lead to failure in roads, foundations, buried pipelines and other infrastructure exposed to heaving soils. The research developed a model capable of providing engineers with the information necessary to account for, and possibly avoid, these effects when designing such infrastructure. A series of experiments were conducted to produce frost heave in soils in a laboratory. The information gained from these tests was used to both develop and confirm the performance of a frost heave model using established numerical techniques. Finally, the model was used to simulate the upward movement of a buried natural gas pipeline exposed to frost heave in a cold region.

Oxidation of pyrite can significantly affect properties and the behavior of soil and rock in civil construction. Problems with pyritic rock and soil extend globally and across many disciplines. Consequences of pyrite oxidation include heave, concrete degradation, steel corrosion, environmental damage, acid mine drainage, and accelerated weathering of rock with concomitant effects on strength and stability. Affected disciplines include soil science, mining, engineering geology, geochemistry, environmental engineering, and geotechnical engineering. While pyrite problems may be well known in their respective disciplines, there has been to date relatively little cross-disciplinary communication regarding problems with pyritic geomaterials. Thus, there is a need to establish an inter-disciplinary and inter-regional awareness regarding the effects of pyrite oxidation and their prevention or mitigation. This engineering research is a compilation of information about geotechnical problems and engineering behavior of pyritic rock and soil, the underlying physicochemical processes, site investigation strategies, and known problematic formations. Several case histories documenting consequences of pyrite oxidation are provided. The results of chemical analyses performed on pyritic shale samples from a formation with acknowledged heave problems are presented. Digital data and ESRI's ArcGIS digital mapping program were used to create maps showing results of sampling and testing performed during this study. Appendices include mitigation options, results of a practitioner survey, chemical test procedures, a glossary, a visual identification key for sulfidic geomaterials, and a summary table of the literature review for this research. / Master of Science

Sulfate-bearing soils are a problem in highway construction as they combine with materials used for lime stabilization to form minerals, particularly ettringite, that expand and induce heave in the stabilized soil. This research involves quantifying sulfate in soils that may be potentially used in highway construction using electromagnetic induction. The objectives are to: 1) document electrical conductivity (EC) variability within selected sites that contain sulfate-bearing materials, and 2) determine if electromagnetic induction has potential for locating hazardous levels of sulfate-bearing materials. The 0.43 ha study area is located in the Blackland Prairies and is a Vertisol known to contain gypsum at the time of site selection. Apparent EC using a model EM38 electromagnetic induction instrument was measured at 200 locations in July and November 2003, using a sampling grid with 5-m spacings. Representative rows and columns were selected from the map of apparent electrical conductivity, and soil cores taken to a depth of 1.5 m at 29 points. Soil samples were obtained by dividing cores into depth increments of 0 to 25 cm, 25 to 75 cm, and 75 to 150 cm. Laboratory analyses were run for each sample and included moisture content, EC and soluble cations and anions of the saturated paste extract, and percent gypsum. Elevation measurements were made to determine if changes in elevation related to EC measurements. Apparent EC proved to be more successful at detecting soluble salts during the dry sampling period (July) when the effect of soil moisture content was less. For July data, EC and gypsum were significantly correlated in the deepest samples (r2 = 0.51 and 0.15, respectively) to apparent EC. Further, soluble sulfate was significantly correlated to apparent EC (r2 = 0.30) at a depth of 25 to 75 cm. Results suggest that the EM38 can be used successfully to map variability of soil salinity across a field, but although correlation exists between apparent EC and sulfate-bearing materials, it is not sufficiently strong to serve as a good predictor for conditions surrounding lime-induced heave in soil.

Horizontal Directional Drilling (HDD) has been used internationally for the trenchless installation of utility conduits and other infrastructure. However, the mud loss problem caused by excessive mud pressure in the borehole is still a challenge encountered by trenchless designers and contractors, especially when the drilling crosses through cohesionless material. Investigation of mud loss problem is necessary to apply HDD with greater confidence for installation of pipes and other infrastructure. The main objectives of this research have been to investigate the maximum allowable mud pressure to prevent mud loss through finite element analysis and small scale and large scale laboratory experiments. The recent laboratory experiments on mud loss within sand are reported. Comparisons indicate that the finite element method provides an effective estimation of maximum mud pressure, and “state-of-the-art” design practice- the “Delft solution” overestimates the maximum mud pressure by more than 100%. The surface displacements exhibit a “bell” shape with the maximum surface displacement located around the center of the borehole based on the data interpreted using Particle Image Velocimetry (Geo-PIV) program. A parametric study is carried out to investigate the effect of various parameters such as the coefficient of lateral earth pressure at rest K0 on the maximum allowable mud pressure within sand. An approximate equation is developed to facilitate design estimates of the maximum allowable mud pressure within sand. A new approach is introduced to consider the effects of coefficient of lateral earth pressure at rest K0 on the blowout solution within clay. The evaluations using finite element method indicate that the new approach provides a better estimation of the maximum allowable mud pressure than the “Delft solution” in clay when initial ground stress state is anisotropic (K0 ≠1). Conclusion of this research and suggestions on future investigation are provided. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2009-01-14 12:23:35.069

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2017. / Submitted by Raquel Almeida (raquel.df13@gmail.com) on 2017-05-05T16:24:10Z No. of bitstreams: 1 2017_TássioMeloLinhares.pdf: 3677540 bytes, checksum: 0ebe53822753f1624bbab44e8f171fc9 (MD5) / Approved for entry into archive by Raquel Viana (raquelviana@bce.unb.br) on 2017-05-30T11:17:23Z (GMT) No. of bitstreams: 1 2017_TássioMeloLinhares.pdf: 3677540 bytes, checksum: 0ebe53822753f1624bbab44e8f171fc9 (MD5) / Made available in DSpace on 2017-05-30T11:17:23Z (GMT). No. of bitstreams: 1 2017_TássioMeloLinhares.pdf: 3677540 bytes, checksum: 0ebe53822753f1624bbab44e8f171fc9 (MD5) Previous issue date: 2017-05-30 / Este trabalho apresenta o desenvolvimento, análise e comparação de diferentes metodologias para o projeto de compensadores de heave em coluna de perfuração. Primeiramente, é apresentada uma revisão dos trabalhos já realizados, presentes na literatura. Na sequência, é apresentado um estudo da modelagem da coluna de perfuração. Continuando os estudos, uma metodologia de projeto de compensador de heave passivo é apresentada e realizada em um protótipo de pequena escala. Com o intuito de obter maiores níveis de atenuação, projetos de compensadores ativos são realizados. Assim, o estudo de observadores, estimadores e filtros, como o filtro de Kalman é desenvolvido. Três metodologias de controle ativo são apresentadas, alocação de polos, alocação de polos com rejeição de perturbação (usando planicidade diferencial) e controle robusto backstepping. Por fim, os resultados das simulações numéricas são apresentados e analisados. / This master thesis presents the development, analysis and comparison of different heave compensator methodologies for drill string. Firstly, a review of previous studies about the subject is presented. Next, is presented a study of drill string modelling. Following the studies, a methodology to design a passive heave compensator is develop and validated by using a small scale prototype. In order to obtain higher levels of attenuation, active heave compensators are designed. Hence, the study of observers, estimators and filters, such as Kalman filter is developed. Three methodologies of active controls are presented, pole placement, pole placement with disturbance rejection using flatness and backstepping robust control. Finally, numerical simulations results are presented and analysed.

Suction piles are used for anchoring the mooring lines at the seafloor. One of the challenges of their installing is the occurrence of the heave resonance of the pile-cable system and possibly the heave induced pitch resonance during the lowering process. When the heave and/or pitch frequency of the vessel which operates the lowering of the pile matches the heave natural frequency of the pile-cable system, the heave resonance may occur, resulting in large heave oscillations of the pile and thus significantly increasing loads on the lowering cable and lowering devices. Furthermore, the large heave may resonantly induce the pitch of a pile. To predict and possibly mitigate the heave/pitch resonance of the pile-cable system during the lowering process, it is crucial to under the mechanism of heave induced pitch resonance and estimate the added-mass and damping coefficients of the pile-cable system accurately. The model tests of the forced heave excitation of pile models were first conducted to investigate the added-mass coefficient for a pile model with different opening area ratios at its top cap at the Haynes Coastal Engineering Laboratory of Texas AandM University. In the model tests, it was observed that the resonant heave may occur if the heave excitation frequency matches the related heave natural frequency and the pitch resonance may be induced by the heave resonance. The results of the following theoretical analysis and numerical simulation of the heave excitation of the pile-cable system are found to be consistent with the related measurements, which is helpful to further understand the physics of lowering a pile-cable system. The results of this study may be used to determine the magnitudes of total heave added-mass and damping coefficient of a pile and the heave natural frequency of the pile-cable system based upon its main characteristics. The heave induced resonant pitch is found to occur when 1) the pitch natural frequency is roughly equal to one half of the heave natural frequency and 2) the heave excitation frequency is approximately equal to the heave natural frequency. If only one of the two conditions is satisfied, no significant pitch resonance will occur. These results may have important implications to the operation of lowering offshore equipment to the seafloor in deep water.

This thesis is titled The influence of a nonlinear Power Take Off on a Wave Energy Converter. It looks at the effect that having a nonlinear Power Take Off (PTO) has on an inertial referenced, slack moored, point absorber, Wave Energy Converter (WEC). The generic device studied utilizes relative heave motion between an axi-symmetric cylinder and an internal mass, for the PTO to operate between. The PTO is the part of the WEC that transforms the relative motion into electricity. In this work, three different types of nonlinear PTO and a linear PTO are presented, tested, analysed and compared. The three nonlinear PTO types are: • A PTO that extracts energy in only one direction, either in relative compression or expansion. • A linear PTO and an additional endstop or peripheral PTO, that can only extract energy when the relative position of the internal mass has reached a pre-determined position. • A PTO that has damping forces that are quadratically proportional to the relative velocity. A numerical simulation has been built based upon a Runge-Kutta time series progression. The model uses the summation of the excitation force from the waves, the radiation force from the movement of the cylinder, the buoyancy force and the PTO forces. These combine to cause acceleration of the mass of the external cylinder, with an equal and opposite PTO force acting on the internal mass. The excitation force and added mass values are obtained from the boundary element method software, WAMIT. Prony’s method is used to obtain an approximate radiation force, based upon the radiation time force history. This numerical model operates on both a 1:40 scale and a full sized model. The numerical model finds the optimal PTO parameters, for different PTO setups, in irregular sea states. This optimum is based on the power extracted as well as indications of the reliability and lifetime of the system. The numerical simulation presents results showing how the nonlinearity of the PTO influences the motions of the WEC, resulting in dissimilarities between the Response Amplitude Operator (RAO) results, obtained from regular seas, and the Linear Transfer Function (LTF), found from irregular sea testing. The experimental model has been tested in the Curved Wave Tank facility at the University of Edinburgh, with a 1:40 scaled model. It used a central rod both as a support structure and to limit the movement of the cylinder and internal mass to heave. Between the cylinder and internal mass a spring and pneumatic damper operate in parallel, in various setups. It was tested in regular and irregular sea states and the position of the internal mass and cylinder was monitored. The experimental model was tested to ascertain the time series motions, RAO, LTF, the relative phase between the bodies and the power extracted for different wave climates. The numerical and experimental work were compared to allow confidence in both models. They showed relatively good agreement for the RAOs, LTFs and predictions of the relative phase but there was discrepancies in the predicted power for both regular and irregular seas. This difference is due to the difficulties in obtaining the relative velocities in the experimental model, resulting in a significant error in power prediction, since the power is proportional to the square of the relative velocities. The conclusions show that having a mono-directional PTO as opposed to a bi-directional PTO results in an approximately equal or greater power extraction in a variety of different sea states. An additional endstop or peripheral damper can increase the total power that a WEC extracts, in some situations, and may be advantageous depending upon the other potential benefits it brings to the WEC.

Plataformas semi-submersíveis, utilizadas como estruturas flutuantes na prospecção e exploração de petróleo em águas profundas, têm sua geometria composta basicamente por elementos horizontais totalmente submersos (pontoons), pelo convés, e por elementos verticais que cruzam a superfície livre (colunas), estes últimos ligando os pontoons ao convés. Tal geometria é eficaz para manter reduzidas as oscilações sob a ação de ondas, mormente o heave, bem como para prover flutuação, área de convés e estabilidade estática compatíveis com a missão. Neste trabalho aplicam-se modelos bastante simplificados para representação de características geométricas e dos atributos acima mencionados. De fato, pontoons e colunas são representados por trechos de cilindros, enquanto que as oscilações sob ondas são determinadas a partir de formulação semelhante à Equação de Morison. Tais modelos compõem um processo de otimização para determinar dimensões principais e proporções que satisfaçam certos requisitos quanto ao peso, à área de convés, à estabilidade estática e ao heave. Resultados numéricos para as oscilações sob ondas são confrontados com dados experimentais obtidos para plataformas em escala reduzida ensaiadas no canal de ondas do Laboratório de Engenharia Naval e Oceânica da EPUSP, observando-se boa aproximação. O processo de otimização é aplicado a situações descritas na literatura, chegando-se a resultados compatíveis com aqueles publicados, com a vantagem da simplicidade dos modelos analítico-numéricos aqui adotados. / Semi-submersible platforms, which are used as floating structures for oil production and exploration in deep waters, have their geometry composed basically of totally submerged horizontal elements (pontoons), the deck, and vertical elements that cross the free surface, these latter linking the pontoons to the deck. This geometry is efficient for keeping the oscillations due to wave excitation at small levels, specially the heave, as well to provide floatation, deck area and static stability compatible to the platform?s mission. In the present work, rather simplified models are applied for the representation of the geometric characteristics and of the other above mentioned attributes. In fact, pontoons and columns are represented by cylinders, and oscillations due to waves are determined by a formulation similar to Morison?s equation. These models take part in an optimization process for the determination of the main dimensions and proportions that satisfy certain requirements concerning weight, deck area, static stability and the heave. Numerical results for the oscillations due to waves are compared to experimental data obtained for scaled platforms tested in the wave channel of the Naval and Oceanic Engineering Laboratory of EPUSP, leading to reasonable approximations. The optimization process is applied to some cases described in the Literature, leading to results compatible with the published ones, but with the advantage of the simplicity of the analytic-numerical models here adopted.