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Pore Pressure Generation and Shear Modulus Degradation during Laminar Shear Box Testing with Prefabricated Vertical DrainsKinney, Landon Scott 01 December 2018 (has links)
Liquefaction is a costly phenomenon where soil shear modulus degrades as the generation of excess pore pressures begins. One of the methods to mitigate liquefaction, is the use of prefabricated vertical drains. Prefabricated vertical drains provide a drainage path to effectively mitigate the generation of pore pressures and aid in shear modulus recovery. The aims of this study were to define shear modulus degradation vs. shear strain as a function of excess pore pressure ratio; define the effects of prefabricated vertical drains on the behavior of pore pressure generation vs. shear strain; and to define volumetric strain as a function of shear strain and excess pore pressure ratios. A large-scale laminar shear box test was conducted and measured on clean sands with prefabricated vertical drains spaced at 3-feet and 4-feet. The resulting test data was analyzed and compared to data without vertical drains. The results show the effect of increasing excess pore pressure ratios on shear modulus and curves where developed to encompass these effects in design with computer programing like SHAKE or DEEPSOIL. The data also suggests that prefabricated vertical drains effectively mitigate excess pore pressure build-up, thus increased the shear strain resistance before pore pressures were generated. Regarding volumetric strain, the results suggests that the primary factor governing the measured settlement is the excess pore pressure ratio. This indicates that if the drains can reduce the excess pore pressure ratio, then the resulting settlement can successfully be reduced during a shaking event. The curves for shear modulus vs. cyclic shear strain as function of pore pressure ratio were developed using data with high strain and small strain which leaves a gap of data in the cyclic shear strain range of 0.0001 to 0.01. Further large-scale testing with appropriate sensitivity is needed to observe the effect excess pore pressure generation on intermediate levels of cyclic shear strain.
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Accuracy Assessment of Shear Wave Elastography for Arterial Applications by Mechanical TestingLarsson, David January 2014 (has links)
Arterial stiffness is an important biometric in predicting cardiovascular diseases, since mechanical properties serve as indicators of several pathologies such as e.g. atherosclerosis. Shear Wave Elastography (SWE) could serve as a valuable non-invasive diagnostic tool for assessing arterial stiffness, with the technique proven efficient in large homogeneous tissue. However the accuracy within arterial applications is still uncertain, following the lack of proper validation. Therefore, the aim of this study was to assess the accuracy of SWE in arterial phantoms of poly(vinyl alcohol) cryogel by developing an experimental setup with an additional mechanical testing setup as a reference method. The two setups were developed to generate identical stress states on the mounted phantoms, with a combination of axial loads and static intraluminal pressures. The acquired radiofrequency-data was analysed in the frequency domain with retrieved dispersion curves fitted to a Lamb-wave based wave propagation model. The results indicated a significant correlation between SWE and mechanical measurements for the arterial phantoms, with an average relative error of 10 % for elastic shear moduli in the range of 23 to 108 kPa. The performed accuracy quantification implies a satisfactory performance level and as well as a general feasibility of SWE in arterial vessels, indicating the potential of SWE as a future cardiovascular diagnostic tool.
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Simple Techniques for the Implementation of the Mechanics of Unsaturated Soils into Engineering PracticeOh, Won Taek January 2012 (has links)
Over the past 50 years, several advancements have been made in the research area of the mechanics of unsaturated soils. These advancements can be categorized into two groups; (i) development (or improvement) of testing techniques (or apparatus) to determine the mechanical properties of unsaturated soils and (ii) development of (numerical, empirical or semi-empirical) models to estimate the variation of mechanical properties of unsaturated soils with respect to suction based on the experimental results. Implementation of the mechanics of unsaturated soils in conventional geotechnical engineering practice, however, has been rather limited. The key reasons for the limited practical applications may be attributed to the lack of simple and reliable methods for (i) measuring soil suction in the field quickly and reliably and (ii) estimating the variation of mechanical properties of unsaturated soils with respect to suction.
The main objective of this thesis research is to develop simple and reliable techniques, models or approaches that can be used in geotechnical engineering practice to estimate sol suction and the mechanical properties of unsaturated soils. This research can be categorized into three parts.
In the First Part, simple techniques are proposed to estimate the suction values of as-compacted unsaturated fine-grained soils using a pocket penetrometer and a conventional tensiometer. The suction values less than 300 kPa can be estimated using a strong relationship between the compressive strength measured using a pocket penetrometer and matric suction value. The high suction values in the range of 1,200 kPa to 60,000 kPa can be estimated using the unique relationship between the initial tangent of conventional tensiometer response versus time behavior and suction value.
In the Second Part, approaches or semi-empirical models are proposed to estimate the variation of mechanical properties of unsaturated soils with respect to suction, which include:
- Bearing capacity of unsaturated fine-grained soils
- Variation of bearing capacity of unsaturated fine-grained soils with respect to matric suction
- Variation of initial tangent elastic modulus of unsaturated soils below shallow foundations with respect to matric suction
- Variation of maximum shear modulus with respect to matric suction for unsaturated non-plastic sandy soils (i.e. plasticity index, Ip = 0 %)
In the Third Part, approaches (or methodologies) are suggested to simulate the vertically applied stress versus surface settlement behavior of shallow foundations in unsaturated coarse-grained soils assuming elastic-perfectly plastic behavior. These methodologies are extended to simulate the stress versus settlement behavior of both model footings and in-situ plates in unsaturated coarse-grained soils.
The results show that there is a reasonably good comparison between the measured values (i.e. soil suction, bearing capacity, elastic and shear modulus) and those estimated using the techniques or models proposed in this thesis research.
The models (or methodologies) proposed in this thesis research are promising and encouraging for modeling studies and practicing engineers to estimate the variation of mechanical behavior of unsaturated soils with respect to matric suction.
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Negative energy elasticity and a model for the behavior of the residual strain in doubly cross-linked gels fabricated by shear strainYou, Therese January 2020 (has links)
Doubly cross-linked gels were fabricated based on tetra-poly(ethylene glycol) (Tetra-PEG) by shear strain. These are gels with two network structures present in the same polymeric network. The second network structure is introduced by applying a mechanical field to the first natural network structure. These doubly cross-linked gels indicated a negative energy elasticity supporting earlier findings where the energy elasticity was found significantly negative for Tetra-PEG gel. Acquired results indicate implications for past research on the elasticity of polymer gels where the energy contribution was approximated to zero. Obtained results also indicated that the modulus of rigidity for the doubly cross-linked gels is constant regardless of applied shear strain during fabrication. This would indicate that the same second network structure is formed for the interval of 25-800% applied shear strain. The residual strain for the fabricated gels can be well-described using an exponential fitting of the apparent shear modulus of the first network structure and an expression derived from the two-network theory and classic rubber theory. These theories also seem to predict the experimental residual strains for lower strain regions (<100%) quite well. However for larger strain regions (>100%) non-linear effects seem to affect the results causing a deviation. A slight increased modulus of rigidity was noted for the doubly cross-linked gels compared to the regular Tetra-PEG gel. However as the reproducibility of the concluded measurements could not be confirmed during this thesis the results are not conclusive and only indicate the conclusions mentioned above.
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Mechanical characterization of two-dimensional heterostructures by a blister testCalis, Metehan 24 May 2023 (has links)
As the family of two−dimensional(2D) materials has grown, two−dimensional heterostructure devices have emerged as great alternatives to replace conventional electronic materials and enable new functionality such as flexible and bendable electronics. The fabrication and performance of these devices depend critically on the understanding and ability to manipulate the mechanical interplay between the stacked materials. In this dissertation, we investigate adhesive interactions and determine the shear modulus of heterostructure devices made from Molybdenum Disulfide (MoS2). MoS2 has been attracting attention recently due to its semiconductor nature (having a direct band gap of 1.9 eV) along with its exceptional mechanical strength and flexibility.
As the first step of our research, we suspended MoS2 flakes grown through chemical vapor deposition (CVD) over substrates made of metal (gold, titanium, chromium), semiconductor (germanium, silicon), insulator (silicon oxide), and semi-metal (graphite). Then, by creating pressure differences across the membrane, we forced MoS2 to bulge upward until we observe separation from the surface of the substrates. We demonstrated that MoS2 on graphite has the highest work of separation within the tested surface materials. Furthermore, we measured considerable adhesion hysteresis between the work of separation and the work of adhesion. We proposed that surface roughness and chemical interactions play a role in surface adhesion and separation of 2D materials. These experiments are critical to guiding the future design of electrical and mechanical devices based on 2D materials.
Next, we measured the effective shear modulus of MoS2/few−layer graphene (FLG) heterostructures by employing a blister test. Again, by introducing a pressure differential across the suspended MoS2 membrane over the FLG substrate, the MoS2/FLG heterostructure peeled off from the silicon oxide surface once the critical pressure is exceeded. Incorporating a modified free energy model and Hencky’s axisymmetric membrane solution, we determine the average effective shear modulus of the heterostructure. This is the first experimental measurement of the shear modulus of heterostructure devices using a blister test and this platform can be extended to determine the shear modulus of other 2D heterostructures as well. / 2024-05-24T00:00:00Z
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Previsão da curva tensão-recalque em solos tropicais arenosos a partir de ensaios de cone sísmico / Prediction of stress-settlement curve on tropical sandy soils based on seismic cone testSouza, Tiago de Jesus 19 September 2011 (has links)
Apresenta-se neste trabalho a aplicação de um método para a previsão da curva tensão-recalque de fundações diretas assentes em solos tropicais arenosos a partir de resultados de ensaios de cone sísmico (SCPT). Os locais estudados foram os campos experimentais de fundações da EESC/USP - São Carlos e da UNESP-Bauru, onde existem resultados de provas de carga realizados a diferentes profundidades, assim como resultados de ensaios SCPT. As previsões realizadas apresentaram bons resultados, após ajustes dos parâmetros f e g, pois as curvas tensão-recalque estimadas foram próximas a aquelas obtidas a partir de provas de carga em placa, para as profundidades maiores que 1,5 metros. Verifica-se assim a aplicabilidade do método, após seu ajuste, para reproduzir a curva tensão-recalque neste tipo de solo, empregando uma abordagem mais racional, com menor dependência de correlações empíricas. Destaca-se nesta pesquisa que existe uma variabilidade dos resultados de ensaios SCPT e de provas de carga que está relacionada com a mudança de sucção no solo. Para o campo experimental de São Carlos foi possível ainda fazer uma avaliação da variabilidade nas previsões realizadas, pois existe maior número de resultados de ensaios de campo e provas de cargas disponíveis. / It is presented in this dissertation the use of a method for predicting the stress-settlement curve of shallow foundations on tropical sandy soils based on seismic cone (SCPT) test results. The studied sites were the experimental research sites from USP - São Carlos, and UNESP - Bauru, Brazil, where there are results from plate load tests conducted at various depths, as well as SCPT test results. The stress-settlement curve predictions show good results, after adjusting the parameters f and g, because the estimated curves were close to those obtained from plate load tests, to depths greater than 1.5 meters. The applicability of the method, after its adjustment, to reproduce the stress-settlement curve for this type of soil, was verified employing a more rational approach with less reliance on empirical correlations. It is highlighted in this research that there is variability on SCPT and plate load test results, which is related to the change in soil suction. It was also possible to access the variability on the prediction for the USP São Carlos site, since there is a greater number of in situ and plate load tests in this site.
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Geostatic stress state evaluation by directional shear wave velocities, with application towards geocharacterization at Aiken, SCKu, Taeseo 09 November 2012 (has links)
Evaluations of stress history and the geostatic state of stress of soils are ascertained on the basis of field geophysical measurements that provide paired complementary types of shear waves. It is well-established that multiple types of shear waves occur in the ground due to their directional and polarization properties. The shear wave velocity (Vs) provides the magnitude of small strain stiffness (G0) which depends on effective stress, void ratio, stress history, and other factors (cementation, age, saturation). Herein, this study examines a hierarchy of shear wave modes with different directions of propagation and particle motion from in-situ geophysical tests (HH, VH, and HV) and laboratory bender element data. A special compiled database from well-documented worldwide sites is assembled where full profiles of stress state, stress history, and several paired modes of Vs profiles have been obtained from crosshole tests (CHT), downhole tests (DHT), and rotary crosshole (RCHT). Reference profiles of the lateral stress coefficient (K0) are available from direct in-situ measurements (self-boring pressuremeter, hydrofracture, and push-in spade cells). Stress history is documented in terms of yield stress ratio (YSR) from consolidation testing and careful engineering geology studies. A methodology is developed that relates both the YSR and K0 to stiffness ratios obtained from directional shear wave velocities. In further efforts, means to extract reliable shear wave profiles from continuous downhole testing via a new GT autosource and seismic piezocone testing are outlined and applied to results from three test sites in Windsor/VA, Norfolk/VA, and Richmond/BC.
A driving impetus to this research involves the geologic conditions at the US Dept. of Energy's Savannah River Site (SRS) in South Carolina. Here, the overburden soils in the upper 60 m depths consist of very old Miocene and Eocene sediments, primarily layered deposits of sands, clayey sands, silty sands, and interbedded clays which exhibit an apparent and unusual stress history profile. Special geologic conditions include the dissolutioning of old calcareous sediments (Santee Formation) at depths of 40 to 50 m below grade, similar to karstic limestone deposits. As a consequence, caves, voids, and infilled soft soil zones occur within the soil matrix at these elevations, probably resulting in localized collapse of the overlying soil column. Based on conventional laboratory and in-situ test data conducted during geotechnical investigations at SRS, available interpretative relationships for assessing the soil stress history and geostatic stress states show scattered and inconsistent results. Complications abound in the systematic assessments of these geomaterials due to effects of very old ageing, cementation, desiccation, and diagenesis, as evidenced by unusual in-situ shear wave velocity profiles that decrease in magnitude with depth, as measured by CHT and DHT. Based on the findings of this study, it is recommended that a new set of shear wave velocity measurements be made at SRS to obtain HH waves (and complementary VH waves) needed for an independent assessment of YSR in the upper soil column.
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Dynamic properties of soils with non-plastic finesUmberg, David, 1987- 18 June 2012 (has links)
The results from an experimental study on the dynamic properties of sand with nonplastic silt are presented. Combined resonant column and torsional shear equipment is used to evaluate the effects of confining pressure, shearing strain, frequency, and number of cycles of loading on the dynamic properties of silty sand. The goal of this study is to determine if relationships in the literature for sands and gravels are accurate for predicting the shear modulus and material damping characteristics of soil with nonplastic fines or if the incorporation of a fines content parameter improves predictions. This goal was primarily accomplished by reconstituting and testing samples of an alluvial deposit from Dillon Dam, Dillon, Colorado according to predetermined gradation curves with variable amounts of non-plastic fines. Among the findings of this investigation are: (1) soil parameters such as Cu and D50 can be related to dynamic properties of soils with up to 25% fines, (2) the effects of non-plastic fines on the small-strain dynamic properties of soils are not very pronounced for soils with less than 25% fines, and (3) an increase in the amount of non-plastic fines in uniform soils or soils with more than 25% fines generally results in lower values of small-strain shear modulus, higher values of small-strain material damping, and more linear G/Gmax - log([gamma]) and D - log([gamma]) curves. The effect of non-contacting, larger granular particles in a finer soil matrix is also investigated along with the impact of removing larger particles from laboratory samples. / text
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NEPTUNE-CANADA BASED GEOPHYSICAL IMAGING OF GAS HYDRATE IN THE BULLSEYE VENTWilloughby, E.C., Mir, R, Scholl, Carsten, Edwards, R.N. 07 1900 (has links)
Using the NEPTUNE-Canada cable-linked ocean-floor observatory we plan continuous, real-time monitoring of the gas hydrate-associated, “Bullseye” cold vent offshore Vancouver Island. Our group inferred the presence of a massive gas hydrate deposit there, based on the significant resistivity anomaly in our controlled-source electromagnetic (CSEM) dataset, as well as anomalously heightened shear moduli, from seafloor compliance data. This interpretation was confirmed by drilling by IODP expedition 311 (site U1328), which indicated a 40 m thick gas hydrate layer near the surface. Sporadic venting and variations in blanking in yearly single-channel seismic surveys suggest the system is evolving in time. We are preparing two stationary semi-permanent imaging experiments: a CSEM and a seafloor compliance installation. These are designed not only to assess the extent of the gas hydrate deposit, but also for long-term monitoring of the gas hydrate/free gas system. The principle of the CSEM experiment is to input a particular electromagnetic signal at a transmitter (TX) dipole on the seafloor, and to record the phase and amplitude of the response at several seafloor receiver (RX) dipoles, at various TX-RX separations. The data are sensitive to the underlying resistivity, which is increased when conductive pore water is displaced by electrically-insulating gas hydrate. The experiment is controlled onshore, and can be expanded to include a downhole TX. Repeated soundings at this site, over several years, will allow measurement of minute changes in resistivity as a function of depth, and by inference, changes in gas hydrate or underlying free gas distribution. Similarly, the displacement of pore fluids by solid gas hydrate will affect elastic parameters. Thus, seafloor compliance data, the transfer function between pressure and seafloor displacement time series, most sensitive to shear modulus as a function of depth, will be gathered continuously to monitor the evolution of the gas hydrate distribution.
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In situ Charakterisierung der viskoelastischen und elektrochemischen Eigenschaften von Poly(3,4-ethylendioxythiophen)Peipmann, Ralf 29 February 2012 (has links) (PDF)
Poly(3,4-ethylendioxythiophen) (PEDOT) ist ein Kunststoff der zur Gruppe der intrinsisch leitfähigen Polymere (ILP) zählt. Aufgrund seiner chemischen und thermischen Stabilität findet er Verwendung in antistatischen Verkleidungen und als Elektrodenmaterial. PEDOT (und andere ILP) zeigen aufgrund ihrer Schaltbarkeit zwischen (reduzierten, ) neutralen und oxidierten Zuständen unterschiedliche Eigenschaften wie Leitfähigkeit, Farbe oder Viskoelastizität.
Im Rahmen dieser Arbeit wurden die elektrochemischen und viskoelastischen Eigenschaften von PEDOT-Filmen untersucht. Dabei wurde die Quarzmikrowaage (QCM) in Verbindung mit potentiostatischen (Potentialsprung, PS) und potentiodynamischen (Cyclovoltammetrie, CV) elektrochemischen Methoden verwendet, so dass in situ elektrochemische und mechanische Eigenschaften der Filme zugänglich waren. Zur Bestimmung der viskoelastischen Eigenschaften wurde ein Auswertealgorithmus entwickelt, welcher auf ein mathematisches Modell zur Bestimmung des Schermoduls nach Efimov zurückgreift.
Während der Herstellung wurden Parameter wie Lösungsmittel, Leitsalz, Vorpolarisations- und Abscheidungspotential variiert und die erhaltenen Filme bezüglich Schermodul und Morphologie charakterisiert. Es konnte gezeigt werden, dass die Elektrolytzusammensetzung einen entscheidenden Einfluss auf die viskoelastischen Eigenschaften der Filme besitzt, welche mit der Morphologie der Filme korrelieren.
Des Weiteren wurden die Änderungen der viskoelastischen Eigenschaften dieser Filme untersucht, welche während dem elektronischen Schalten zwischen neutralem und oxidiertem Zustand aufgrund des Ionenaustausches erfolgen. CV- und PS-Experimente zeigten, dass die viskoelastischen Eigenschaften durch Konzentration und pH-Wert des Elektrolyten beeinflusst werden und in unterschiedlicher Weise auf die Potentialänderungen reagieren.
Durch den Einbau von Magnetit-Partikeln in die Schichten konnten Hybridfilme erhalten werden, deren Eigenschaften durch das Anlegen eines äußeren Magnetfeldes beeinflusst werden können. Solche Filme zeigten in einem äußeren Magnetfeld (0,7T) höhere Schermodule und einen stark unterdrückten Ionenaustausch.
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