Browsing by Subject "Geotechnical"
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Item Analytical and Experimental Studies of Drag Embedment Anchors and Suction Caissons(2011-08-08) Beemer, RyanThe need for experimental and analytical modeling in the field of deep water offshore anchoring technologies is high. Suction caisson and drag embedment anchors (DEA) are common anchors used for mooring structures in deep water. The installation process of drag embedment anchors has been highly empirical, employing a trial and error methodology. In the past decade analytical methods have been derived for modeling DEA installation trajectories. However, obtaining calibration data for these models has not been economical. The development of a small scale experimental apparatus, known as the Laponite Tank, was developed for this thesis. The Laponite Tank provides a quick and economical means of measuring DEA trajectories, visually. The experimental data can then be used for calibrating models. The installation process of suctions caissons has benefited from from a more rational approach. Nevertheless, these methods require refinement and removal methodology requires development. In this thesis, an algorithm for modeling suction caisson installation in clay has been presented. An analytical method and modeling algorithm for removal processes of suction caissons in clay was also developed. The installation and removal models were calibrated to field data. These analytical and experimental studies can provide a better understanding of installation of drag embedment anchors and the installation and removal of suction caissons.Item The development of a geotechnical GIS-based database in Austin, TX(2011-05) Lawrence, Robert Hoff; Gilbert, Robert B. (Robert Bruce), 1965-; Maidment, David R.Geographic Information Systems (GIS) are useful in analyzing and visualizing database information. Specifically, the field of geotechnical engineering stands to benefit from a database encompassing GIS; as, geotechnical data varies spatially. The City of Austin Water Utility realized the advantages of a geotechnical database utilizing GIS which led to the motivation of designing a database for Austin, Texas. The main objective is to provide a detailed explanation of the design of a GIS-relational geotechnical database for Austin, Texas. In addition, several examples of useful methods of analyzing geotechnical data spatially are included. The examples show the identification of faults, the uses of structural contour maps, summarization of data through plots and tables, and analyzing temporal piezometric conditions. The idea of a database is to organize and store data in a basic efficient format so that information is not duplicated. Database queries are then used to combine and rearrange the data within the database through relationships. The queries are then connected to GIS for intelligent visualization. This process is designed specifically for the geologic conditions that exist in Austin, Texas. Understanding the geotechnical engineering state of practice is important when designing a database that will encompass geotechnical data for a given region. The City of Austin relies on experience and the geotechnical report filing systems to initially plan future projects around geologic conditions. With the help of a geotechnical database, the information from geotechnical reports is a “computer click” away. Also, the geotechnical data from multiple reports is viewable at one time in both a 2 and 3 dimensional environments through GIS. Database features coupled with GIS tools proves to be an effective way for engineers and geologists to use geotechnical data.Item Development of a multi-measurement confined free-free resonant column device and initial studies(2010-08) Pucci, Martin Joseph; Stokoe, Kenneth H.; Gilbert, Robert B.This study is comprised of three major parts. The first part involved the development of a multi-measurement, confined, free-free resonant column device. This device was developed to improve upon traditional manually excited, vacuum-confined, free-free methods. The device is capable of testing specimens with diameters up to 6-in., under confinements upwards of 50 psi. The device is composed of a seismic-source system, a data acquisition system and a specimen support and confinement system. The seismic source system is used to induce small-strain constrained compression waves, and longitudinal and torsional stress waves in the specimen. The data acquisition system is used to measure: (1) direct travel time of constrained compression waves, (2) longitudinal resonance in unconstrained compression, and (3) torsional resonance. From these measurements, constrained compression wave velocity, Vp, unconstrained compression wave velocity, Vc, and shear wave velocity, Vs, can be determined. With these wave velocities, small-strain, constrained modulus, Mmax, Young’s modulus, Emax, and shear modulus, Gmax can be determined. Poisson’s ratio is also calculated with the wave velocities. Finally, from the resonance measurements, small-strain material damping in unconstrained compression, DCmin, and in shear, DSmin, can be evaluated. The second part of this study involved verification tests with materials of known dynamic properties. The tests were performed with a manufactured aluminum specimen, ASTM graded Ottawa sand, and crushed rock aggregate base. The results compared well with previous results from similar tests. The third part of this study involved testing artificially cemented ASTM graded Ottawa sand. Cement contents (by weight) of 0.0, 0.5, 1.0 and 2.0%, were used to observe the effect of cementation with curing time at a constant confining pressure of 5 psi. The overall effect of cementation was: (1) a large increase in stiffness, and (2) an increase in material damping. The key effects related to cementation versus curing time are: (1) the increase in wave velocities are reasonably proportional to an increase in cement content up to a curing time of about 5 to 7 days, and (2) after a curing time of 5 to 7 days time the velocity increase with time seems to be similar for all cemented specimens. Additionally, the 2% cemented specimen was tested to observe the effect of confining pressure. The stiffness of this specimen was quite insensitive to confining pressure as was the material damping.Item Failure mechanics, transport behavior, and morphology of submarine landslides(2010-12) Sawyer, Derek Edward; Flemings, Peter Barry, 1960-; Mohrig, David; Lavier, Luc; Hornbach, Matthew; Shipp, R. Craig; Nikolinakou, MariaSubmarine landslides retrogressively fail from intact material at the headwall and then become fluidized by strain weakening; the final deposits of these flows have low porosity, which controls their character in seismic reflection data. Submarine landslides occur on the open slope and also localized areas including margins of turbidite channel-levee systems. I develop and quantify this model with 3-D seismic reflection data, core and log data from Integrated Ocean Drilling Program Expedition 308 (Ursa Basin, Gulf of Mexico), flume experiments, and numerical modeling. At Ursa, multiple submarine slides over the last 60 ky are preserved as mass transport deposits (MTDs). Retrogression proceeded from an initial slope failure that created an excavated headwall, which reduced the horizontal stress behind the headwall and resulted in normal faults. Fault blocks progressively weakened until the gravitational driving stress imposed by the bed slope exceeded soil strength, which allowed the soil to flow for more than 10 km away from the source area. The resulting MTDs have lower porosity (higher bulk density) relative to non-failed sediments, which ultimately produces high amplitude reflections at the base and top of MTDs. In the laboratory, I made weak (low yield strength) and strong flows (high yield strength) from mixtures of clay, silt, and water. Weak flows generate turbidity currents while moving rapidly away from the source area. They create thin and long deposits with sinuous flow features, and leave behind a relatively smooth and featureless source area. In contrast, strong flows move slowly, do not generate a turbidity current, and create blocky, highly fractured source areas and short, thick depositional lobes. In Pleistocene turbidite channels of the Mississippi Fan, deep-seated rotational failures occurred in the flanking levees. The rotational failures displaced material into the channel from below where it became eroded by turbidity flows. This system achieved a delicate steady state where levee deposition and displacement along the fault into the channel was balanced by erosion rate of turbidity flows. This work enhances our understanding of geohazards and margin evolution by illuminating coupled processes of sedimentation, fluid flow, and deformation on passive continental margins.Item Laboratory investigation into evaluation of sand liquefaction under transient loadings(2015-12) Kwan, Wing Shun; El Mohtar, Chadi Said; Kramer, Steven L; Rathje, Ellen M; Cox, Brady R; Kallivokas, Loukas FThe current laboratory procedures for evaluating liquefaction potential are still the same as 40 years ago, with minor updates. The complex seismic loading motions are simplified to a series of uniform harmonic sinusoidal loading cycles with amplitudes related to the maximum amplitude of a given ground motion; liquefaction resistance is then evaluated as the load generating liquefaction in a predefined number of harmonic loading cycles. The simplified methods of loading and resistance characterizations are a crude proxy and provide limited information in predicting the time of liquefaction triggering and therefore, the expected effects/damage of seismic events. Specific details of the time of soil liquefaction within a ground motion can be better understood from laboratory testing. Among the available element-level types of cyclic testing, cyclic simple shear (CSS) tests are the most popular and commonly used. The CSS tests provide a satisfactory simulation of seismic induced in-situ stresses. A testing program consisting of a series of multi-stage undrained direct simple shear tests was performed using the hydraulically-actuated GCTS cyclic simple shear apparatus. The apparatus had been modified and upgraded so that it is capable of applying user-specified, transient loading histories to Nevada Sand soil samples. Reconstituted specimens were prepared by the wet pluviation method at two different densities, 40% and 70%, followed with back-pressure saturation and K0 consolidation. The shearing phase was conducted in three distinctive stages: (1) Scaled transient stress histories, (2) modulated sinusoid with a taper-up shape stress histories, (3) static monotonic loads. All shearing stages were performed under continuous undrained conditions. This research program had two major motivations. The first motivation is to provide element-level tests subjected to transient loadings, so that the soil responses of excess pore pressure generation and shear strain along the time domain can be measured. The transient loading was selected from a suite of ground motions with different spectral and temporal characteristics to cover a wide range of possible ground motions. The second motivation is to investigate the performances of four Intensity Measures (IMs): CAV5, Arias Intensity, Normalized Energy Demand and PGA magnitude. These IMs were proven to be more efficient predictors of soil responses than peak acceleration. The experiments provide a database that can systematically illustrate the response of liquefiable materials subjected to transient ground motions before and after liquefaction; such a database was virtually non-existent prior to this study. Therefore, the data generated in this study supports the development of improved and more informative procedures for the evaluation of liquefaction potential, the effects of liquefaction, post-liquefaction responses, and more accurate constitutive models for liquefiable soils.Item Measuring liquefaction-induced deformation from optical satellite imagery(2014-05) Martin, Jonathan Grant; Rathje, Ellen M.Liquefaction-induced deformations associated with lateral spreading represent a significant hazard that can cause substantial damage during earthquakes. The ability to accurately predict lateral-spreading displacement is hampered by a lack of field data from previous earthquakes. Remote sensing via optical image correlation can fill this gap and provide data regarding liquefaction-induced lateral spreading displacements. In this thesis, deformations from three earthquakes (2010 Darfield, February 2011 Christchurch, and 2011 Tohoku Earthquakes) are measured using optical image correlation applied to 0.5-m resolution satellite imagery. The resulting deformations from optical image correlation are compared to the geologic conditions, as well as field observations and measurements of liquefaction. Measurements from optical image correlation are found to have a precision within 0.40 m in all three cases, and results agree well with field measurements.