Pile foundations are extensively used to support various structures that are constructed in soft/loose soils, where shallow foundations would be considered ineffective due to low bearing capacities and large settlements. The design of these structures to accommodate lateral applied loads in particular, usually imposed by winds, water and earth pressures, has gained popularity over the past few decades. The behaviour of horizontally loaded piled foundations is a complex soil-structure interaction problem and is usually concerned with the relative stiffness between the pile and the surrounding soil, where the relative stiffness is a function of both the stiffness and properties of the pile and the stiffness of the soil. Many design assumptions and methods used for pile foundations are based on the principles observed from metal piles. This raises the question of the validity and accuracy of assumptions and methods for the use of analysing and designing reinforced concrete piles, that exhibits highly non-linear material behaviour and changing pile properties after cracking. Due to the elastic behaviour of metal sections, these methods typically only focus on the soil component of the soil-structure interaction problem, only allowing changes and non-linear behaviour of the soil surrounding the pile to take place upon load application, mostly disregarding the behaviour and response of the pile itself. The main purpose and objective of the study was to determine whether aluminium sections in a centrifuge could be used to realistically and sufficiently accurately model the monotonic and cyclic response of reinforced concrete piles subjected to lateral loading. This was observed though a number of tests conducted in a geotechnical centrifuge on scaled aluminium and reinforced concrete piles, subjected to both monotonic and cyclic loading. After conducting the tests on both the scaled aluminium and reinforced concrete piles in the centrifuge it was concluded that aluminium sections cannot be used to accurately model and predict the lateral behaviour of reinforced concrete piles. Both the scaled aluminium and reinforced concrete piles proved to model the concept of laterally loaded piles quite well regarding bending at low loads. However, even at low lateral loads, the observed response of the scaled reinforced concrete was significantly different than that observed from the scaled aluminium pile. Furthermore, as the magnitude of the applied load and bending increased, the scaled reinforced concrete pile cracked, resulting in non-linear behaviour of the section under loading, which was not the case for the scaled aluminium pile that remained uncracked. This contributed to the difference in behaviour between the piles studied, therefore, the true material behaviour and failure mechanisms involved with reinforced concrete piles were not replicated by using a scaled aluminium pile section. The non-linear behaviour of the scaled reinforced concrete pile after cracking affected both the behaviour of the pile, as well as the response of the soil surrounding the pile, in contrast with the behaviour observed from the scaled aluminium pile. / Dissertation (MEng)--University of Pretoria, 2020. / The Concrete Institute / Concrete Society of Southern Africa / WindAfrica project / Civil Engineering / MEng (Structural Engineering) / Unrestricted

Research performed on the subject of dynamic soil-structure interaction (SS) concerning railway bridges is presented in this thesis with the focus on simply supported railway bridges supported by shallow foundations in soil strata on bedrock. The research aims to obtain insight into the SSI of high-speed railway bridges and to provide recommendations on how to model the soil-bridge system from a design perspective. A three-dimensional (3D) simply supported soil-bridge model was first developed and the effects from model assumptions made on the soil-foundation system was evaluated in a 3D setting (paper I). The soil-foundation system was then refined and a model assumptions study was performed in order to evaluate the effects of model assumptions on impedance functions, including the influence of the permanent load acting on the soil-foundation system (paper II). Finally, a study of the assembled soil-bridge system was performed in an extensive parametric study including a set of 2D bridge models in combination with a set of shallow foundations in soil strata on bedrock (paper III). A supplementary section related to paper III was also added in this thesis, showing the effects of the substructure mass. The model assumptions made when creating the soil-foundation model and the soil-bridge model can be very important and must be made with care. The permanent load acting on the soil-foundation systems of shallow foundations may alter the impedance functions significantly. The substructure mass may alter the behavior of the soil-bridge system depending on its magnitude, and neglecting it gives inaccurate results. The 3D effects of SSI do not cause high vibrations due to modes other than the first bending mode, and assuming a 2D bridge model is generally acceptable. The effects of SSI on the soil-bridge systems with shallow soil strata are largely dependent on the ratio between the natural frequency of the bridge and the fundamental frequency of the soil. Depending on the value of this ratio, the effect of including SSI in bridge models may contribute to the bridge obtaining a negligible, conservative, or non-conservative response, as compared to the bridge with the assumption of non-flexible supports. / Forskning i syfte att utröna effekten av dynamisk jord–struktur-interaktion (SSI)på järnvägsbroar presenteras i denna avhandling med huvudfokus på fritt upplagdabroar med stöd av plattgrundlagda fundament i jordar på fast berggrund. Forsknin-gen syftar till att ge förståelse för interaktionen mellan jord och järnvägsbroar samtatt ge rekommendationer på hur systemet kan modelleras ur ett designperspektiv.En tredimensionell (3D) fritt upplagd jord–bromodell utvecklades först och effek-terna av modellantaganden gjorda på jord–grundläggningssystemet utvärderadesi en 3D miljö (artikel I). Jord–grundläggningssystemet förfinades och en studiegenomfördes för att utvärdera effekterna av modellantaganden på impedansfunk-tioner, inklusive påverkan av den permanenta belastningen som verkar på jord–grundläggningssystemet (artikel II). Slutligen utfördes en omfattande parametriskstudie av det sammansatta jord–brosystemet där en uppsättning tvådimensionella(2D) bromodeller kombinerades med en uppsättning jordar (artikel III). Ett kom-pletterande avsnitt relaterat till artikel III lades till i denna avhandling som visareffekterna av massan av underbyggnaden på jord–brosystemet.De modellantaganden som görs vid skapandet av jord–grundläggningsmodeller ochjord–bromodeller kan vara mycket viktiga och bör utföras med varsamhet. Den per-manenta belastningen som verkar på jord–grundläggningssystemet kan väsentligtförändra impedansfunktionerna. Massan av underbyggnaden kan vidare ändra re-sponsen i jord–brosystemet, beroende på dess storlek, och att försumma den kan gefelaktiga resultat. De 3D effekterna av SSI orsakar inte höga vibrationer på grundav andra moder än den första böjmoden, och att anta en 2D bromodell är såledesgenerellt sett motiverat.Effekterna av SSI på jord–brosystemet i grunda jordar beror till stor del av kvotenmellan brons naturliga frekvens och jordens fundamentala frekvens. Beroende påvärdet på denna kvot kan effekten av att inkludera SSI i bromodeller bidra till attbron får en försumbar, konservativ, eller icke-konservativ respons, i jämförelse medbron med antagandet om fasta upplag. / <p>QC 20200903</p>

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20327号 / 工博第4264号 / 新制||工||1661(附属図書館) / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 三村 衛, 教授 大津 宏康, 准教授 肥後 陽介 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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In this investigation, seismic response of retaining walls constructed with cohesive and cohesionless backfill materials was studied. Fully dynamic analysis based on finite difference method was used to evaluate the performance of retaining walls during the earthquake. The analysis response was verified by the experimental study conducted on a retaining wall system with cohesive backfill material in the literature. The effects of cohesion and free-field peak ground acceleration (PGA) on seismic earth thrust, the point of action of earth thrust, and maximum wall moment during the earthquake were compared with analytical and experimental solutions. The numerical results were compared with various analytical solutions. The motion characteristics of the retaining wall during the earthquake were also considered. The relative displacement of the walls with various backfill cohesions, under different ground motions, and free-field PGAs were investigated. Current analytical and empirical correlations developed based on Newmark sliding block method for estimating retaining wall movement during earthquakes were compared with the numerical approach. Consequently, fragility analyses were conducted to determine the probability of damage to the retaining walls. To evaluate the fragility of the studied models, specific failure criterion was chosen for retaining walls based on the suggested methods in practice. Using numerical approaches, the effects of soil-wall interaction and wall rigidity on the seismic response of retaining walls were also evaluated in earthquake conditions for both cohesive and cohesionless backfill materials. According to the findings, practical correlations were presented for conducting the seismic design of retaining walls.

The focus of this study is on potential problems resulting from construction on expansive soils in Kibaha region, Tanzania. For the fact that most of the affected structures are founded on expansive soils, a clear understanding of the soil behaviour and their interaction with structures, specifically as they relate to shallow foundations, has been of more interest to the study in order to evaluate properly the source of the problem. The geotechnical behaviour of expansive clay soils is investigated by looking into the geomorphologic, geological and climatic conditions and mineralogical composition of the soils in the study area. The geotechnical results are linked with the performance of the foundation as well as structures. Two sites, representative of known problem-areas in Kibaha were selected for geotechnical tests. Geotechnical site investigation consisted of open trial pits, profile description and the collection of both disturbed and undisturbed samples. The collected samples were submitted to soil laboratories at KTH and DIT for mineralogical composition tests, natural water content, density, Atterberg limits and swell tests (free swell and swelling pressure). The results of this investigation indicate that soil in Kibaha contains clay (31%), have high liquid limit (59%) and plastic limit (37%) which indicate high potential swell. Since swell potential and swell pressure are key properties of expansive soils, the swell parameters were measured by free swell tests and one-dimensional oedometer swell tests respectively. The free swell ranged from 100% to 150% and the swell pressure was in the region of 45 kPa. The properties of expansive soils were confirmed by the x-ray diffraction test which showed the presence of montmorillonite in the soil. It is from this fact that the source of the problem is in the expansive soils coupled with poor building materials. Physical conditions of the surveyed properties in the area confirmed the hypothesis of building damages due to poor building materials triggered by expansive soils. In support of the obtained data, the actual behaviour of the foundations is supplemented with prototypes of strip foundations whose performances are to be monitored over a long period. Finally, suggested are the ways forward to solve the problem of foundation on expansive soil. / QC 20101118

Highway bridges are considered to be one of the most susceptible constituents of transportation networks when they are subjected to severe natural hazards such as earthquakes and environmental exposures like subfreezing temperatures. To facilitate and enhance pre-hazard event mitigation and post-hazard emergency response strategies, probabilistic risk assessment methodologies have attracted increased attention, recently. Seismic fragility assessment is one of the probabilistic techniques which predicts the damage risk of the structure for a given hazard level. While fragility curves can be developed using different methods, such as expert-based, empirical, experimental, analytical, and hybrid, analytical fragility curves are perceived to be the most reliable and least biased technique. Seismic isolation systems are prevalently used in bridge structures to mitigate the damage risk of bridge components against natural hazards. However, the effectiveness of implementing recently emerged isolators such as Stable Unbonded Fiber Reinforced Elastomeric Isolators (SU-FREI) should be examined by developing analytical fragility curves of retrofitted bridges and quantifying the mitigation in the damage probability of different bridge components. In this regard, incorporating the Soil-Structure Interaction (SSI) is critical since the lateral response of bridges relies on the relative stiffness of bridge components, such as columns and isolators and the supporting soil. In addition, all bridge components are exposed to environmental stressors like subfreezing temperature that can alter the seismic response of bridges. In the first phase of this thesis, a seismic fragility assessment is carried out on an existing multi-span continuous reinforced concrete bridge. Two bridge representations are developed to simulate the as-built bridge along with its retrofitted counterpart utilizing SU-FREI. An Incremental Dynamic Analysis (IDA) is conducted using 45 synthetic ground motion records developed for eastern Canada and damage limit states are applied to generate fragility curves and determine the probability of damage to different bridge components. Bridges are analyzed in longitudinal and transverse directions, independently, and component- and system-level fragility curves are developed. In the second phase, the previously generated bridge models are expanded to incorporate the SSI effects by introducing the pile groups under piers and abutments. Several interactions including deck-abutment, abutment-embankment, pile-soil, and pile-soil-pile interactions are considered. A significant challenge in this phase is the accurate simulation of the lateral and vertical behavior of pile groups since all pile groups comprised of closely-spaced vertical and battered piles. A ground motion suite consisting of 45 ground motions has been selected, which reflects the seismicity of the bridge site. IDA is conducted to monitor the seismic performance of the bridge from the elastic linear region up to collapse. Fragility curves, which serve as an important decision-support tool have been developed to identify the potential seismic risk of the bridge. In the third phase, a multi-hazard assessment is carried out by conditioning the previously developed bridge models (i.e. monolithic fixed-base, isolated fixed-base, monolithic with SSI, and isolated with SSI) to a range of room and subfreezing temperatures and applying a seismic excitation, simultaneously. The cold temperature behavior of the constitutive materials of different bridge components, namely, concrete, reinforcing steel, rubber, and the supporting soil are studied and reflected in the bridge models. IDA is performed and damage potential of different bridge components are quantified. In summary, it is demonstrated that SU-FREI is a competing alternative for seismic isolation of bridges by offering potentially less manufacturing time and cost, lower weight, and easier installation which is an attractive feature for accelerated bridge construction applications. In all three phases, it is shown that the bridges which are isolated using SU-FREI have improved seismic performance in comparison with monolithic bridges by exhibiting lower probability of damage to the primary bridge components like columns and pile caps and transferring the damage to less important components such as abutments at which damage does not cause bridge closure. In addition, it is shown that seismic isolation using SU-FREI can effectively mitigate the seismic demand and damage potential of the constitutive components of a bridge supported by weak soil. While occurrence of seismic events along with an environmental stressor such as cold temperature can drastically jeopardize the functionality of a bridge supported by weak soil, it is demonstrated that seismic isolation using SU-FREI can significantly alleviate the probability of damage to bridge components. / Dissertation / Doctor of Philosophy (PhD)

Two-dimensional analysis of four types of water-filled tube dams is carried out: an apron-tube dam, a single baffle tube dam, a sleeved tube dam, and a stacked tube dam. Since the analysis of the water-filled tube dam involves highly nonlinear geometric deformations and interactions with soil, fluid, and structure, it is solved numerically with the explicit finite difference program FLAC. The tube is numerically modeled with beam elements. The predicted contact regions are modeled with interface elements. The Mohr-Coulomb constitutive model is used for the soil. Water inside and outside of the tube is modeled as hydrostatic pressure and the pressures are continuously updated as the configuration of the tube is changed. The change of the internal water pressure head (IWPH) for maintaining a constant tube area during the deformation is simulated. The simulation is achieved by two iterative procedures, the secant method and the factored secant method. The numerical analysis results show good agreement with the experimental results overall: the deformation of the tube(s), the IWPH changes, and the critical external water heights. From the numerical simulation of the experiments and the parametric studies, the behavior of each type of water-filled tube dam is clarified. Also, the failure modes of the tube dams are examined. The failure mode of a tube dam depends on the configuration and IWPH of the tube dam and the characteristics of the soil surface. / Ph. D.

The 1999 Kocaeli Earthquake (M=7.4) struck northwestern Turkey on August 17, 1999 and caused significant damage in urban areas located along Izmit Bay. The sites that suffered the greatest damages were located primarily in areas of poorest soil conditions, typically containing soft clays and silts and/or loose, liquefiable sands. Because the affected region is heavily developed with infrastructure and there is a preponderance of poor soils, a wide range of soil improvement measures had been used to mitigate anticipated earthquake damages throughout the region. Following the earthquake and significant aftershocks, Virginia Tech researchers traveled to Turkey to investigate the affected area to document geotechnical field performance. Primary focus of the Virginia tech team was given to investigating the performance of improved soil sites and reinforced soil structures. The sites were subjected to ground motions ranging from about 0.10g to 0.35g. The site locations ranged from 0 to 35 km from the zone of energy release. This dissertation presents in detail, the findings from the two most instructive sites. The investigation of these sties involved field reconnaissance, field and laboratory testing of soils, seismic analysis, numerical modeling, and other analytical work. / Ph. D.

A water-filled geomembrane tube is considered for the purpose of temporary flood protection. With proper design, this tube can be a cheap and efficient breakwater, temporary levee, or cofferdam. This thesis considers a single tube resting on clay and sand foundations. A finite difference program, FLAC, is used in the numerical analyses. The tube is assumed to be infinitely long, and it is modeled two-dimensionally. Beam elements are used to model the tube. The tube is inflated with water. The hydrostatic pressure in the tube is converted to point loads and applied at the beam nodes in the direction perpendicular to the chord connecting two adjacent nodes. Two of FLAC's built-in soil models are used: elastic and Mohr-Coulomb. The Mohr-Coulomb model is used in all the cases except the preliminary analyses, in which the elastic soil model is used. The Mohr-Coulomb soil model is able to model the soil's nonlinear stress-strain and path-dependent deformation behavior. A tube without external water is placed on clay with various shear strengths to study how the clay consistency affects the height and the stresses in the tube. A tube with external water on one side is placed on medium dense sand. A wooden block is placed on the side opposite the floodwater. Three types of block geometry and two sizes are studied. The floodwater level is increased until the system fails. Three failure modes, rolling, sliding, and piping, are studied. The effect of pore pressure on these failure modes is examined. The influence of a filter placed under part of the tube and block is also investigated. The tube's tensile forces, shear forces, moments, and settlements are included. Soil stresses and pore pressures at the soil-tube interfaces are computed. The cross-section of the tube at various external water levels, and the pore pressures in the soil, are calculated. These results are compared with experimental results that were obtained by graduate students in geotechnical engineering at Virginia Tech. / Master of Science