Browsing by Subject "Geotechnical engineering"
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Item Analysis of spatial variability in geotechnical data for offshore foundations(2010-12) Cheon, Jeong Yeon; Gilbert, Robert B. (Robert Bruce), 1965-; Zornberg, Jorge; Manuel, Lance; Mohrig, David; El Mohtar, ChadiDeep foundations, such as piles and suction caissons, are used throughout an offshore oil and gas production facility in deepwater. Ideally, the values of geotechnical properties for foundation design are determined by results from geotechnical investigation programs performed at the site of the foundation. However, the locations for facilities are not known exactly when soil borings are drilled and the footprint of a facility in deepwater can be very large with numerous foundation elements spread out over miles. Therefore, it is not generally feasible to perform a site-specific investigation for every foundation element. The objective of this research is to assess, analyze and model spatial variability in geotechnical properties for offshore foundations. A total of 97 geotechnical investigations from 14 offshore project sites covering the past twenty years of deepwater development in the Gulf of Mexico are compiled into a database. The geologic setting is primarily a normally to slightly overconsolidated marine clay, and the property of interest for the design of deep foundations is the undrained shear strength. The magnitude and characteristics of variability in design undrained shear strengths are analyzed quantitatively and graphically. Geostatistical models that describe spatial variability in the design shear strength properties to the distance away from the available information are developed and calibrated with available information from the database. Finally, a methodology is presented for incorporating the models into a reliability-based design framework to account for spatial variability in foundation capacity. Design examples are presented to demonstrate the use of the reliability methodology. Based on the design undrained shear strength profiles for the past 20 years in this Gulf of Mexico deepwater area, the design undrained shear strength varies spatially but does not depend on the time or method for site investigations. There are nonlinear spatial relationships in the point shear strength laterally and vertically due to stratigraphy such that depth-averaged shear strengths are correlated over further distances than point shear strengths. The depositional forces are an important factor causing spatial variations in the undrained shear strength, with greater variation and less spatial correlation in the more recent hemipelagic deposits (about upper 60 feet) than the deeper turbidite deposits and along the shelf versus off the shelf. The increased conservatism required in deep foundation design due to spatial variability when site specific strength data are not available is generally small with less than a five percent increase required in design capacity in this geologic setting.Item Commissioning of the multi-use static/dynamic large-scale soil testing table(2012-08) Stromberg, Michael Paul; El Mohtar, Chadi Said; Gilbert, RobertThis thesis presents the details of designing and commissioning the multi-use static/dynamic large-scale soil testing table. The table was developed with the intention of creating a large scale testing apparatus versatile enough to carry out several different types of testing on a large scale. This report describes the background research done to develop the testing table concept and the thinking that went into each component. The apparatus itself consists of a shake table with a laminar soil container (inside dimensions L:100cm W:50cm H:65cm) and a top which can be lowered to apply overburden pressures on specimens. It is set up to run both static and cyclic tests on large soil samples. The final design allows for performing shaking tests with a non-fixed top, static and dynamic simple shear tests, and direst shear tests with minimal changes to the table configuration. The table has separate control and data acquisition systems which are necessary to run and record tests. All components of the table will be explained thoroughly within the thesis. Preliminary testing was done with the table to determine how well it is functioning and what needs to be done to further improve it. Static simple shear and cyclic simple shear tests were both run, and while the table showed some flaws, the results seem promising. It is determined that with proper instrumentation and after addressing some small issues, the testing table can be a useful and versatile tool in the future. This thesis will outline the strengths and flaws of the table as currently constructed and determine what the future applications for this testing apparatus will be.Item Decision support for enhanced oil recovery projects(2010-08) Andonyadis, Panos; Gilbert, Robert B. (Robert Bruce), 1965-; Lake, Larry W.Recently, oil prices and oil demand are rising and are projected to continue to rise over the long term. These trends create great potential for enhanced oil recovery methods that could improve the recovery efficiency of reservoirs all over the world. The greatest challenges for enhanced oil recovery involve the technical uncertainty with design and performance, and the high financial risk. Pilot tests can help mitigate the risk associated with such projects; however, there is a question about the value of information from the tests. Decision support can provide information about the value of an enhanced oil recovery project, which can assist with alleviating financial risk and create more potential opportunities for the technology. The first objective of this study is to create a new simplified method for modeling oil production histories of enhanced oil recovery methods. The method is designed to satisfy three criteria: 1) it allows for quick simulations based on only a few physically meaningful input parameters; 2) it can create almost any potential type of realistic production history that may be realized during a project; and 3) it applies to all nonthermal enhanced oil recovery methods, including surfactant-polymer, alkali-surfactant polymer, and CO₂ floods. The developed method is capable of creating realistic curves with only four unique parameters. The second objective is to evaluate the predictive method against data from pilot and field scale projects. The evaluations demonstrate that the method can fit most realistic production histories as well as provided ranges for the input parameters. A sensitivity analysis is also performed to assist with determining how all of the parameters involved with the predictive method and the economic model influence the forecasted value for a project. The analysis suggests that the price of oil, change in oil saturation, and the size of the reservoir are the most influential parameters. The final objective is to establish a method for a decision analysis that determines the value of information of a pilot for enhanced oil recovery. The analysis uses the predictive method and economic model for determining economic utilities for every potential outcome. It uses a decision-based method to ensure that the non-informative prior probability distributions have an unbiased, consistent, and rational starting point. A simple example demonstrating the process is discussed and it is used to show that a pilot test provides some valuable information when there is minimal prior information. For future work it is recommended that more evaluations are performed, the decision analysis is expanded to include more input parameters, and a rational and logical method is developed for determining likelihood functions from existing information.Item Experimental in-plane behavior of a generic scale model drag embedment anchor in Kaolinite test beds(2011-05) McCarthy, Katelyn Barbara; Gilbert, Robert B. (Robert Bruce), 1965-; Rathje, Ellen M.The trajectory and capacity are key components of the design of drag embedment anchor and drag-in vertically loaded anchors. This experimental testing program quantifies two factors that describe the anchor trajectory and capacity: the equilibrium bearing factor (Ne) and the tangential bearing factor (Ne). These factors can aid in the development of a numerical model of anchor behavior. A magnetometer device is used to track the orientation and location of the anchor during drag embedment. The results of the experimental testing program were compared with the results from a predictive model. The experimental program consisted of drag embedment tests with various testing conditions including different anchor line diameters and different initial pitch orientations. The results with the different anchor lines indicated that thinner anchor lines cause the anchor to dive deeper in the soil. The different initial pitch results indicate that regardless of the initial pitch of the anchor, the anchor rotates to a unique pitch trajectory within 2 fluke lengths.Item Geotechnical characterization of bauxite residue (red mud)(2015-08) Gore, Matthew Stephen; Gilbert, Robert B. (Robert Bruce),1965-; Zornberg, Jorge G; Caldwell, Todd G; El Mohtar, Chadi S; Katz, Lynn E; Juenger, Maria GBauxite residue is the iron-oxide rich mine waste from the processing of bauxite ore for the extraction of alumina through the Bayer process. The Bayer process uses caustic soda, high pressure, and high temperature to leach alumina from ferruginous residue slurry (bauxite residue or red mud). This leaching process produces alumina to ferruginous/bauxite residue at ratios of 1:1 to 1:4 with the end result being billions of tons of bauxite residue waste (4 billion tons worldwide by this year (2015)). The residue is associated with being chemically basic (average pH = 12), high in heavy metals, and has shown low level naturally occurring radioactive materials (NORMs) (equivalent to other household building materials like granite, gypsum, and marble). The objectives of this research were to characterize bauxite residue using the traditional methods developed in the field of geotechnical engineering for classifying soils, study possible source and processing effects that may contribute to the behavior of the material, and assess the feasibility of the material for beneficial reuse as a civil engineering building material. Characterization of the material included index properties (grain size distribution, specific gravity, and plasticity), powder x-ray diffraction, compaction behavior, and performance behavior that included compressibility, hydraulic conductivity, shear strength, and erosion resistance. The research focused on the potential beneficial reuse of bauxite residue in the form of fill for a flood protection levee. The research findings are that bauxite residue is a fine-grained, low plasticity material that would be classified under USCS classifications as a ML soil. Bauxite residue's compaction behavior is like a plastic, fined-grained material in compaction. It compacts at higher optimum moisture content and lower maximum dry densities than similar fine-grained soils (CH, CL, and ML) for both standard and modified Proctor efforts. Bauxite residue has a reasonably low hydraulic conductivity that provides low flow rates for a levee application. The material exhibited high drained shear strength in comparison to other fine-grained materials but, if not compacted, does exhibit static liquefaction potential similar to most fine-grained tailings that have low plasticity. Bauxite residue is comparable to a typical compacted clay in terms of compressibility, both in regards to its own compressibility and its total unit weight concerning the applied pressure to the subgrade. Bauxite residue demonstrates a high resistance to erosion. Lastly, bauxite residue has a high pH (pH > 13) that must be addressed before the material could be used in a levee. The issue can be resolved using neutralization or encapsulation by another soil. Overall, in terms of geotechnical properties, bauxite residue shows acceptable characteristics for potential use in a flood protection levee.Item Geotechnical properties of Kaolinite contaminated with a non-aqueous phase liquid(2011-05) Goff, Mary Kathlyn; Gilbert, Robert B. (Robert Bruce), 1965-; El Mohtar, Chadi; Reible, DannyContaminated sites are found all around the world. In order to contain these contaminants, engineers propose capping the contaminated sediments with a sand cap. When capping these contaminants, the sand causes consolidation to occur and could cause a slope failure if the contaminants were on a slope. Investigating the properties of these contaminated sediments allows for proper analysis of a slope failure. The primary objective of this research was to determine the shear strength of contaminated sediments. Since soil samples from actual contaminated sites are highly variable and difficult to explain, the soil used in this research project was mixed and controlled in the lab. A mixture of Kaolinite, water and mineral oil (NAPL, non-aqueous phase liquid) was used for the specimens. Different oil amounts were placed into the specimens to create different scenarios. The different oil combinations included: 100% water, 100% oil, 90% oil, 70% oil, and 50% oil. All of the specimens were fully saturated, and the specimens that had less than 100% oil contained water in the remaining percentage. Consolidated Undrained and Consolidated Drained triaxial tests were performed on the specimens. The constructed specimens were subjected to consolidation stages ranging from 0.6psi to 29psi in confining pressure. The main focus of the study was on low confining pressures. After consolidation the specimens were sheared either undrained or drained. Both tests were utilized in order to see the difference in the pore pressures generated. Failure envelopes were developed for the different oil contents that contained three dimensions included the shear strength, the effective stress, and the pore pressure difference between the pore oil pressures and the pore water pressures. Also, the behavior of oil-dominated versus water-dominated was determined. Results from the 100% water specimens were comparable to previous data. The shear strength for the 100% oil specimens was higher than the 100% water specimens, but lower than the 90% oil and 70% oil specimens. The 50% oil specimens resulted in a great deal of variability on whether the specimen was water-dominated or oil-dominated. The main conclusion was that the Kaolinite had an increase in strength with the introduction of mineral oil.Item Model experiments to measure yield thresholds and trajectories for plate anchors and develop a new anchor concept(2016-08) Gerkus, Hande; Gilbert, Robert B. (Robert Bruce), 1965-; Bradshaw, Aaron S.; Kinnas, Spyros A.; Rathje, Ellen; Cox, BradyThe motivation of this research was to experimentally measure yield thresholds and dive trajectories of model plate anchors and develop a new anchor concept: The Flying Wing Anchor®. The objectives of this study were to (1) develop the understanding of pure loading yield thresholds of simple shaped bearing plates in clay under undrained loading, investigate how the undrained shear strength, sensitivity and plasticity of soil affects the pure loading yield thresholds and compare experimental measurements with theoretical predictions (2) asses the initiation of post-yield movement and dive trajectory of bearing plates, (3) optimize the design of the Flying Wing Anchor® concept based on pure loading yield thresholds, initiation of post-yield movement and dive trajectory in clay, (4) develop a simplified plasticity model to predict the initiation of post yield behavior, dive trajectory and the ultimate holding capacity of the new anchor concept in clay and compare theoretical predictions with experimental measurements. The methodology focuses on experimental testing of model plates and Flying Wing Anchor® concepts in undrained clay. The theoretical calculations are compared with experimental measurements. The pure loading yield thresholds of the bearing plates in clay under undrained loading were measured. The post-yield movement analysis showed an anchor vertically embedded into soil should initially rotate from vertical to dive deeper with drag loading. The initial Flying Wing Anchor® concept is the one-wing Diamond anchor and further optimization resulted in bi-wing concepts of Paloma and the final concept of Speedy anchors. The new anchor concept dives deeper into soil when loaded in tension. At the ultimate embedment depth, the holding capacity is maximized. The lower shear resistance enables deeper penetration into soil. The holding capacity is maximized over the full anchor surface in bearing due to high resistance in normal loading. Anchor can be pulled out of soil in pure shear and reused. Scaled model tests show the new anchor is a promising sustainable and efficient foundation solution for deep-water offshore wind turbines due to efficient installation method, sustained high capacity and horizontal trajectory during failure that prevents anchor to slide out of soil.Item System reliability for bridge bent foundations on driven piles(2013-05) Hall, Taylor Quinn; Gilbert, Robert B. (Robert Bruce), 1965-Modern day bridge foundations are often designed for the maximum loading condition on a single member and each following foundation member often follows the same design. A 4-pile and a 2-pile foundation system were analyzed with an upperbound plasticity model in an attempt to approximately represent the system capacity. A sensitivity analysis was performed to measure the change in the ultimate system capacity by altering the parameters used to define individual pile capacities. The load and the resistance are considered to be normally distributed and are each characterized by a mean and a standard deviation. A first order reliability method was used to measure and account for any system redundancy in the foundation system by predicting a probability of failure based on the load and resistance of the system. Based on the most heavily loaded pile and the analysis performed on the 2-pile and 4-pile foundation systems, the probabilities of failure are lower for the system than for the single pile. This would bring reason to state there is some measurable redundancy in the basic systems analyzed where these systems would once be considered to be non-redundant systems.