Clays, whether deposited on the seafloor or resedimented in the lab, generally exhibit a type of anisotropy called transverse isotropy (TI) due to layering and grain/void orientation from compaction. ...Sediments also experience an array of stress states due to varying geologic conditions. It is important to systematically measure how velocity anisotropy evolves with stress path to improve subsurface geophysical models, understand dynamic stress-strain relationships, and perform informed geotechnical site characterizations. This research experimentally measured velocity anisotropy in intact vs resedimented Boston Blue Clay (BBC), as well as stress path velocity dependence, vertical velocities during undrained shear, and velocity anisotropy from 1 to 10 MPa of resedimented Gulf of Mexico Eugene Island Clay (RGoM-EI). Results for intact versus resedimented BBC agree, and all clays exhibited low horizontal vs vertical velocity anisotropy and inclined compressional wave anisotropy (Thomsen parameters ≤ 0.3). Shear stress was found to affect wave velocity immensely, and results suggest that stress path compression-derived equivalent velocity curves resemble Modified Cam Clay (MCC) iso-porosity ellipses. Undrained shear-derived iso-velocity curves agree with those from normal consolidation as well, implying that porosity/density controls vertical P-wave velocity (Vp) in normally consolidated clays.This thesis also improves upon shear and longitudinal (Vs and Vp) wave velocity measurement technologies developed at Tufts Advanced Geotechnical Laboratory and MIT. Prior technology exhibited signal noise issues that affected horizontal wave velocity interpretation. Additionally, apparatus compressibility was not considered in the previous studies, leading to offset velocity measurements. The signal issue in the horizontal wave arrivals was found to be caused by improper grounding, originating from a shared ground pin of both receiving and sending actuators. Apparatus compressibility was then measured, and for a uniaxial test at 10 MPa axial effective stress, the velocity offset was found to be 13.7 m/s. Since the P-wave velocity range of interest is greater than 1500 m/s in sea water, this deviation produces a 2.5% error in vertical P-wave velocity (VpV). This implies that all prior VpV were overestimated by up to 2.5 percent, though this error is now corrected for in post-processing.
Improving the engineering properties of the subgrade soil by means of chemical stabilization is known to enhance the construction conditions in plastic soils and result in a reduction in design ...thickness requirements of the base, subbase, and wearing course in a layered pavement structure. This can also potentially lead to an increase in pavement life. This study was undertaken to study the effect of hydrated lime and Portland cement used as a stabilizing agents on the strength properties and the cracking resistance of a clayey soil collected from South Dakota. Hydrated lime was mixed with the collected soil by 2%, 3% and 5% and Portland cement was blended at 7%, 9% and 11% by the weight of the soil. Different tests, namely Particle size distribution, Atterberg limits, pH, Proctor test, freeze-thaw (F-T) cycles, unconfined compressive strength, and semicircular bend test were conducted before and after treatment with hydrated lime and Portland cement. The results indicated that use of 1% cement was more effective than 1% lime in improving soil’s shear strength. In general, shear strength of the natural soil was found to become more sensitive to F-T cycles with increasing both Portland cement and hydrated lime contents. The flexural stiffness and fracture energy of the natural soil were found to improve by stabilizing it with both lime and cement. This improvement was more pronounced when Portland cement was used. Reduction in the flexural stiffness and fracture energy of the lime-stabilized soil was found to be more sensitive to F-T cycles than cement-stabilized soil. The only stabilizing agent found to be capable of improving the flexibility index of the natural soil was hydrated lime. Cement-stabilized soil was concluded to be highly brittle and may result in instantaneous propagation of the crack in the whole section after reaching the peak load. Therefore, the use of cement stabilization should be carried out more cautiously to avoid premature crack
The Hawaiian Islands have been a world-famous traveling spot for their unique tropical island view. But the particular geological formation of the islands and their unique locations have always ...proposed challenges for geotechnical engineers and geologists. For example, coral sand is widely encountered in coastal areas of tropical or subtropical regions. It can be found on most beaches in Hawaiian islands. Compared with silica sand, it usually exhibits weaker mechanical performance from the perspective of engineering geology. Thus, necessary soil improvements shall be applied to the coral. Considering the fragile and unique ecosystem, sustainable material with less carbon footprint and less environmental impact would be developed and selected priorly. Moreover, the infrastructures along the island have been facing coastal erosion issues from both physical erosion (waves) and chemical erosion (sea wind and seawater). The road embankment, the house embankment, the harbor, etc often require maintenance to sustain their service time. Due to the topography and climate, the windward side of the coastal area on Oahu is suffering from marine microplastics (MP) pollution issues. Furthermore, as an island state, hurricanes and tsunamis could also threaten the safety of islanders and infrastructures. Therefore, as a geotechnical major Ph.D. student, this dissertation would devote some potential solutions to the challenges. Firstly, a novel alkali-activation-based sustainable binder was developed for coral sand stabilization. The alkali-activated slag (AAS) binder material was composed of ground granulated blast furnace slag (GGBS) and hydrated lime with the amendment of biochar, an agricultural waste-derived material. The biochar-amended AAS stabilized coral sand was subjected to a series of laboratory tests to determine its mechanical, physicochemical, durability, and microstructural characteristics as well as durability. Results show that the addition of a moderate amount of biochar in AAS could improve soil strength, elastic modulus, and water holding capacity by up to 20%, 70%, and 30%, respectively. Moreover, the addition of biochar in AAS had a marginal effect on the sulfate resistance of the stabilized sand, especially at high biochar content. However, the resistance of the AAS-stabilized sand to wet-dry cycles slightly deteriorated with the addition of biochar. Based on these observations, a conceptual model showing biochar-AAS-sand interactions was proposed, in which biochar served as an internal curing agent, micro-reinforcer, and mechanically weak point.Secondly, a state-of-the-art deep-learning algorithm, Mask R-CNN, was utilized for the clayey soil crack detection, locating and segmentation. A comprehensive dataset including 1200 annotated crack images of 256×256 resolution was prepared for the algorithm training and validation. The proposed Mask R-CNN algorithm achieved precision, recall and F1 score of 73.29%, 82.76% and 77.74%, respectively. Besides, the algorithm gained a mean locating accuracy (APbb) of 64.14% and a mean segmentation accuracy (APm) of 47.59%. The detection performance of the Mask R-CNN was also compared with the U-Net in three different scenarios. The test results have demonstrated the superiority of the Mask R-CNN over the U-Net algorithm in crack detection, locating and segmentation and the algorithm could automatically process the crack characterization. Then, this dissertation proposed a state-of-the-art deep learning-based approach, Mask R-CNN, to locate, classify, and segment large marine microplastic particles (fiber, fragment, pellet, and rod). The fully trained Mask R-CNN algorithm was compared with U-Net in characterizing microplastics against various backgrounds. The results showed that the algorithm could achieve Precision=93.30%, Recall=95.40%, F1 score=94.34%, APbb=92.7%, and APm = 82.6% in a 250 images dataset with white background. The algorithm could also achieve a processing speed of 12.5 FPS. The results obtained in this study implied that the Mask R-CNN algorithm is a promising microplastics characterization method that can be potentially used in the future for large-scale surveys. Finally, a video instance segmentation algorithm was trained to locate, identify, and segment soil cracks in a real-time video stream. The algorithm could record the cracks' locations and numbers simultaneously. Besides, the crack ratio of clay could be calculated by crack pixels divided by total clay pixels among the entire soil cracking process. Furthermore, Structure from Motion (SfM) has been applied to reconstruct the 3D soil desiccation models. The soil crack can be detected in a 3D point cloud graph and highlighted. A series of 3D parameters like depth, volume, and cross-section profile can be obtained for future analysis. The proposed video instance segmentation method has demonstrated the potential application for real-time crack alerts and monitoring of geotechnical infrastructures via surveillance cameras.
Aqueous inorganic contaminants, such as cadmium(II), arsenic(III), copper(II), and selenium(IV), present a major threat to human and environmental health. To ensure widespread testing and detection ...of these contaminations, there is a need for inexpensive methods for rapid onsite detection of these contaminants. Voltammetric methods using disposable screen-printed electrodes present a promising option for onsite detection of cadmium(II), arsenic(III), copper(II), and selenium(IV). To fully utilize the potential of voltammetry, methodologies for the simultaneously detection of analytes are required. This thesis discusses two studies to develop methods for rapid simultaneous analysis of mixed analyte solutions. The first study developed a method for the detection of arsenic(III) in the presence of copper(II) concentrations as high as 1.3 ppm. This methodology was developed by optimizing the sample pH, deposition time, deposition voltage, and loading of gold nanostars on the surface of the working electrode. This optimized methodology was tested in solutions with common interferences and was compared with atomic absorption spectroscopy using river water and tap water samples. The second study developed a methodology for the simultaneous detection of cadmium(II), arsenic(III), and selenium(IV). First the optimal reagent for simultaneous detection of the three analytes was selected. Next, the behavior of the analytes in single and mixed analyte solutions was studied. The methodology was evaluated with common interferences and samples of river water. Finally, a data analysis program for the automatic detection and measurement of peak height was developed and tested.
Maintaining ballast condition is an important aspect of maintaining a healthy track infrastructure system. Cyclic train loading over sections of track naturally degrades the ballast which must ...maintain a proper layer thickness and ballast particle gradation to optimally function. Over time, repeated axle loadings deform the ballast layer and degrade the ballast particles changing the effective ballast particle gradation and thus the strength of the track substructure. This behavior is historically handled by maintenance procedures aimed at reinforcing the track structure by strengthening the ballast.Maintenance engineers benefit from detailed information about specific degradation behavior which allows them to perform timely and effective maintenance strategies such as tamping, undercutting and ballast cleaning. Historically, ideal maintenance scheduling has relied heavily on past experience, manual inspection, and field observations. Delaying maintenance past when it is required can cause degradation of track geometry, which can result in safety concerns and substantial track damage. Conversely, performing maintenance too early increases costs. Since track deterioration results in larger financial consequences, railroads tend to err on the side of caution.The research conducted herein focuses on developing a specialized ballast condition evaluation hardware and associated software to quantify ballast condition and failure criteria. SmartRocks are battery-powered wireless devices that resemble a ballast particle that are placed in track within the existing ballast layer and are capable of measuring acceleration and orientation in real time using tri-axial accelerometers and tri-axial gyroscopes. SmartRocks are installed in chosen sections of ballast, operating remotely, and transmitting recorded data to receivers installed on the field side of the track. Using SmartRock data, analysis was conducted to investigate SmartRock behavior, and thus ballast behavior, under various track conditions in an effort to correlate their behavior with known installation site information.To compare individual SmartRock measurements, the data was first subject to a basis change such that all data was in a uniform track coordinate basis. Following, extensive Exploratory Data Analysis (EDA) was conducted to identify and compare SmartRock measurement characteristics using descriptive statistics and unsupervised machine learning methods which are fully explained. Using the available SmartRock data, analysis showed that they behave differently under varying conditions of design and installation. For example, the data clearly shows that SmartRock response from passing trains differed for SmartRocks installed under-tie pads vs. those installed without under-tie pads. It is hypothesized that response data from SmartRocks allows for determinations of ballast behavior which in turn can lead to better understanding of ballast degradation and failure mechanisms. SmartRock response data is analyzed and explained, with examples showing how the data was used to make determinations about the two track sections in which SmartRocks were installed.
Uma das principais funções da geotecnia é avaliar o comportamento de estruturas em contato com o solo. No entanto, a caracterização geotécnica dos maciços de terra não é sempre realizada de modo a ...refletir o comportamento global daquele material, já que os ensaios de caracterização são restritos a locais de extrema importância para o projeto da estrutura. A interação de estruturas de suporte de terra flexíveis com o maciço é um problema altamente indeterminado, as movimentações do maciço afetam as movimentações do paramento e vice-versa. Além disso, as movimentações horizontais estão extremamente relacionadas às pressões de terra e aos esforços que a estrutura está sujeita. Tendo isto em mente, esta dissertação tem como objetivo avaliar a maneira que os parâmetros de resistência do solo, a rigidez do paramento e o faseamento construtivo da estrutura afetam o comportamento de uma parede moldada com três níveis de ancoragens pré-esforçadas. A base da estrutura foi considerada encastrada em um estrato rígido e, portanto, está impedida de deslocar. Para isso, foram realizadas análises computacionais, utilizando diferentes metodologias de análise, método de Winkler e método dos elementos finitos (MEF), de forma a verificar os resultados obtidos por ambos os métodos. Através deste estudo foi possível concluir que o aumento da rigidez do paramento reduz os deslocamentos horizontais da estrutura e consequentemente aumenta as pressões de terra e esforços atuantes na estrutura. No entanto, para o MEF, altos valores de rigidez causam redução mínima do deslocamento, sendo que o deslocamento da estrutura começa a se assemelhar a uma rotação em torno da base. No MEF, o aumento dos parâmetros de resistência do solo geraram redução do deslocamento da estrutura e aumento da pressão de terra e esforços. O mesmo não foi observado para o método de Winkler, os resultados para resistências não drenadas de 25 kPa e 150 kPa foram próximos e para 75 kPa e 300 kPa também. O faseamento construtivo se mostrou indispensável para modelar o comportamento do solo no MEF, variações de 50% do deslocamento da estrutura foram observadas quando as fases construtivas intermediárias foram desconsideradas. Para o método de Winkler, os resultados foram pouco afetados, os esforços praticamente não sofreram alterações e o deslocamento sofreu uma variação de 8%.
Microbially induced desaturation (MID) via denitrification is an emerging ground improvement technique to mitigate liquefaction by stimulating the metabolic processes of native bacteria to produce ...biogas, biominerals and biomass. The production of biogenic gas gradually lowers the degree of saturation of treated soils, thereby dampening the pore pressure response to cyclic loading. However, the production of these metabolic products also alters the hydraulic and mechanical properties of the soil. A series of four tank tests simulating two-dimensional plane strain conditions were performed to evaluate the effectiveness of MID and the resulting changes to the hydraulic properties of the soils. Previous studies have demonstrated the mechanical response for treated homogenous granular soils at the bench scale via vertical injection methods. However, limited knowledge is available on the impact of partial desaturation on the hydraulic properties of the soil, particularly in stratified formations. Treating larger granular soil specimens via lateral injection methods is important for the up-scaling and future commercialization of the process as it may affect injection strategies, and the distribution of substrates and metabolic products. Tank tests were performed on a layered natural soil sediment collected from Richmond, British Columbia, Canada, as well as layered and unlayered laboratory grade Ottawa sands of different grain size distributions. The results demonstrated the effectiveness of treatment upon macro-scale soil properties, and showed how gas formation, migration and entrapment, and resulting degree of desaturation and hydraulic conductivity are affected by micro and macro-stratifications in granular soils.
A geophysical investigation involving ground-penetrating radar (GPR) with soil probing was carried out on the floodplain of Lytle Creek, Murfreesboro, to understand the flood depositions and their ...subsurface lithology. Information was used to determine the watershed boundaries. A 350 MHz and 900 MHz Geophysical Survey Systems Inc. (GSSI) equipment was used for GPR data acquisition, and major interpretation procedures involving dewowing, filtering, and applying automatic gain were carried out. The GPR surveys in this study revealed significant sub-surface stratigraphy of depositional materials along the river channel. Three main characteristic radar facies were identified through the floodplain and bank exposure investigation. The majority of the profiles were noted to have horizontal, wavy, and hyperbolic reflections. The resulting floodplain structure was delineated and found to extend throughout the river channel and having fine-grained deposits (silty loam and silty clay). GPR proved to be a reliable tool in delineating subsurface stratigraphy non-invasively for this study.
The coefficient of earth pressure at rest, Ksub.0, is a significant mechanical parameter, and the investigation of the Ksub.0 of coarse-grained soil has important theoretical significance and ...applicational value in geotechnical engineering. However, there are few studies on the influence of the initial dry density (ρd) on the Ksub.0 of coarse-grained soil due to the limitations of the related test instruments or methods. A series of Ksub.0 tests for two types of coarse-grained soils (rockfill soil and sandy-gravel soil) were conducted based on a newly developed large-scale apparatus to reveal the relationship between the Ksub.0 and ρd of coarse-grained soil. The test results showed that the Ksub.0 of coarse-grained soil decreases with an increase in vertical stress, and this trend tends to be gentle with respect to the increase in vertical stress. The results also implied that there was a negative linear relationship between the Ksub.0 of coarse-grained soil and ρd. Furthermore, a comparative analysis between rockfill soil and sandy-gravel soil indicated that the relative equation proposed by the authors was appropriate for any type of coarse-grained soil with any ρd. Moreover, an empirical equation that can accurately describe the effective relationship of σv and ρd with the Ksub.0 for coarse-grained soil was proposed, and the accuracy of the empirical equations were verified by the Ksub.0 test results concerning sand-gravel soil. Finally, based on the published research findings, the empirical equations' applicability to any coarse-grained soil was verified.
