Knowledge of geotechnical soil properties in the upper meter of the seabed is important for challenges such as scour around submerged structures, management of unexploded ordnances, and generally issues associated with active sediment transport and deposition. Portable free fall penetrometers have been previously used to provide initial information on sediment type, strength, and stratification, but challenges with the calibration of empirical parameters such as the cone factor and strain rate factor hampered the derivation of geotechnical design parameters such as undrained shear strength. This challenge applies particularly in areas of more rare seabed soil conditions such as very soft estuarine sediments. This study aims to advance the analysis procedure of portable free fall penetrometers (PFFP) in soft subaquatic fine-grained soils with natural water contents greater than the liquid limit by estimating the undrained shear strength (su). The logarithmic and power law methods for strain rate correction were investigated at sites in the York River Estuary and yielded a match to vane shear results at a logarithmic multiplier of k=0.1-0.3 and a power law rate exponent of β=0.01-0.03, indicating minimal strain rate effects. Resulting representative cone factors based on sediment strength and profile groupings ranged from 7 to 12 for logarithmic, power law, and no strain correction, and were tested at sites in the Potomac River with similar sediment properties. The PFFP su compared well with mini-vane shear measurements with differences of less than ± 0.5 kPa. Additionally, the PFFP su showed inappreciable differences in strength with or without strain rate application. Therefore, these high water content soils that exhibit little strain rate effects within a soil behavior context, can be better understood through rheological studies. Rheological studies were conducted, and the storage and loss modulus were observed to remain constant when the soil is tested over a range of frequencies. This indicates that the sediment strength is not affected by the rate of soil testing. The outcome of this study is the advanced the use of the PFFP by quantifying the strain rate effects and defining the applicable cone factors for use in estimating the undrained shear strength of soft estuarine marine soils. Furthermore, the understanding of soil behavior of these soils has been explored from rheological context. / Master of Science / Presence of unexploded munitions (UXO) in waterways and coastal environments poses a danger to the populace. UXOs located proud on the seabed can be moved by hydrodynamic forces such as waves and currents to habited areas. This has prompted the need to understand how UXOs interact with the seabed regarding erosion, burial, as well as sinking. Current methods used to detect munitions can lack accuracy from unknown seabed soil conditions. Portable free fall penetrometers (PFFP) are rapid and economical tools that are used to obtain soil information in the seabed. However, the interpretation of the penetrometer data needs to be advanced to get more accurate results of soil strength. In this research, physical soil samples were retrieved and tested in the laboratory. The laboratory results were used to calibrate the PFFP to improve the estimation of soil strength from PFFP. The estuarine soil tested exhibited high water contents raising the question of whether to describe its behavior rather as soil or suspension. Further tests were carried out to study how this soil deforms and flows when a load is applied. The results from this research enable the measuring of strength of the seabed more accurately and improves the understanding of very soft estuarine soil behavior.

Free-fall penetrometers (FFP) are useful instruments for the rapid characterization of seabed sediments. However, the interpretation of FFP data remains largely a skilled task. In order to increase the reliability of results obtained using these instruments, in both expert and non-expert hands, it is advantageous to establish well defined and repeatable procedures for instrument use and data interpretation. The purpose of this research was therefore to develop and refine methods for the interpretation of FFP data. Data were gathered with the FFP Nimrod during two surveys following dredging in Sydney Harbour, Nova Scotia. The challenge of interpreting the data from these two surveys in an efficient and consistent manner was the basis of this work and led to the development of new techniques for improving resolution of the mud-line, identifying areas of erosion and deposition, and qualitatively evaluating the consolidation state of cohesive marine sediments. The method developed for improving the resolution of the mud-line simply describes a procedure of combining the data from different accelerometers with different accuracies and ranges to more clearly define the point of impact with the sea-floor. The method developed to evaluate in-situ sediment consolidation state combines theories of self-weight consolidation and ultimate bearing capacity to predict a range of potential bearing capacities for normally consolidated cohesive sediments. Finally, by combining the previous two methods a third method is proposed for locating areas of potential erosion and deposition. / Master of Science

Free-fall penetrometers (FFPs) are an attractive tool for the rapid characterization of sediments in the nearshore and coastal areas. To improve their measurement capabilities, modern FFPs can be equipped with pore pressure sensors. Pore pressure measurements are extensively used in traditional cone penetration testing, but their usage and interpretation is still limited for FFP testing. This thesis represents an effort to advance the interpretation of pore pressure measurements from FFP testing. Data was collected using the torpedo-shaped FFP BlueDrop during surveys at Herschel Island, YT, Yakutat, AK, Clay Bank, VA, and Yorktown, VA. Additionally, test deployments in the laboratory were performed in kaolin clay. Data analysis was focused on pore pressure measurements during these deployments. Two major advancements regarding current data analysis of FFP pore pressure measurements were explored: 1) a method based on fluid dynamic principles was proposed to correct the pressure recordings for the dynamic flow effects due to the high-velocity fall and impact. The results show that using Bernoulli’s theorem coupled with the concept of pressure coefficients results in good agreement between measured and hydrostatic pressures during the free-fall and initial penetration stage. 2) Pore pressure dissipation curves measured by the penetrometer at rest at maximum penetration depth were also studied. The mechanisms behind the non-standard dissipation curves were explored. The results suggest that non-standard dissipation curves can be interpreted by correcting according to Sully et al.’s (1999) extrapolation technique. The technique can also be used with data from an unsaturated or clogged filter. / Master of Science

Portable Free Fall Penetrometers (PFFPs) are lightweight tools used for rapid and economic characterization of surficial subaqueous sediments. PFFPs vary in weight, shape and size with options for using add-on units. The different configurations enable deployments in various environments and water depths, including the nearshore zone where conventional methods are challenged by energetic hydrodynamics and limited navigable depth. Moreover, PFFPs offer an opportunity to reduce the high site investigation costs associated with conventional offshore geotechnical site investigation methods. These costs are often a major obstacle for small projects serving remote communities or testing novel renewable energy harvesting machines. However, PFFPs still face issues regarding data analysis and interpretation, particularly in energetic sandy nearshore areas. This includes a lack of data and accepted analysis methods for such environments. Therefore, the goal of this research was to advance data interpretation and sediments characterization methods using PFFPs with emphasis on deployments in energetic nearshore environments. PFFP tests were conducted in the nearshore areas of: Yakutat Bay, AK; Cannon Beach, AK; and the U.S. Army Corps of Engineers' Field Research Facility's beach, Duck, NC. From the measurements, the research goal was addressed by: (1) introducing a methodology to create a regional sediment classification scheme utilizing the PFFP deceleration and pore pressure measurements, sediment traces on the probe upon retrieval, and previous literature; (2) investigating the effect of wave forcing on the sediments' behavior through correlating variations in sediment strength to wave climate, sandbar migration, and depth of closure, as well as identifying areas of significant sediment mobilization processes; and (3) estimating the relative density and friction angle of sand in energetic nearshore areas from PFFP measurements. For the latter, the field data was supported by vacuum triaxial tests and PFFP deployments under controlled laboratory conditions on sand samples prepared at different relative densities. The research outcomes address gaps in knowledge with regard to the limited studies available that investigate the sand geotechnical properties in energetic nearshore areas. More specifically, the research contributes to the understanding of surficial sediment geotechnical properties in energetic nearshore areas and the enhancement of sediment characterization and interpretation methods. / PHD

In-situ geotechnical testing of surficial sediment layers in areas of active sediment dynamics can provide essential information about physical and geotechnical variations of sediment properties with regards to active sediment remobilization processes. For example, portable free fall penetrometers (PFFPs) can assist with the detection of mobile sediment layers. They are easy to deploy, and can provide a large spatial coverage in a time- and cost-effective manner. However, they often struggle to provide more detailed information about the properties of mobile sediment layers due to a lack of calibration and validation in existing data sets. Currently, existing sediment samplers often disturb, or ignore the uppermost sediment layers. Simultaneous sediment sampling and geotechnical profiling is needed to fill this gap, and to drive data interpretation forward. A field investigation of surficial sediments was conducted in the wetland waterways of coastal Louisiana in 2014. In-situ tests were conducted using PFFP, and disturbed sediment samples were collected in selected locations. The results allowed us to map changes in sediment strength and stratification, and correlate the geotechnical results to local site characteristics. However, the need for high quality sediment samples for calibration and validation was emphasized by the results. Three different sediment sampler add-on units targeting mobile layers were designed and manufactured based on lessons-learned from the literature. The designs were tested in the laboratory and in the field (Yakutat, Alaska and York River, Virginia) in 2017. The samples were analyzed to understand the influence of different sampler characteristics on collected sample quality, and, to define mobile layer sampler characteristics that enable simultaneous geotechnical testing and the collection of high quality samples. Following field survey campaigns in the York River, Virginia in 2016 allowed to assess surficial sediment layer characteristics and behavior based on a coupled analysis of geotechnical data from in-situ PFFP tests and the sedimentological data collected using box cores and the novel sediment sampler. In summary, novel strategies and instrumentation to carry out simultaneous sediment sampling and geotechnical profiling of seabed surface layers were tested, and new pathways for geotechnical data analysis for the investigation of mobile seabed layers were presented. / PHD

Free-Fall Penetrometer (FFP) testing is an easy and rapid test procedure for seabed sediment characterization favorable to conventional geotechnical testing mainly due to its cost-effectiveness. Yet, FFP testing results are interpreted using empirical correlations, but difficulties arise to understand soil behavior under the high-strain rate (HSR) loading effects during rapid FFP penetration. The numerical simulation of FFP-soil interaction is also challenging. This study aims to numerically analyze FFP testing of saturated loose sands using the particle-based Material Point Method (MPM). The numerical analysis was conducted by simulating calibration chamber FFP tests on saturated loose quartz sand. The numerical results using quasi-static properties resulted in a reaction of the sand softer than the actual calibration chamber test. This implied the necessity of considering HSR effects. After performing parametric analyses, it was concluded that dilation plays an important role in the response of sand-water mixtures. Comparison of dry and saturated simulations showed that FFP penetration increases when the soil is dry and tends to develop a general bearing capacity failure mechanism. This is because the pore water increases the stiffness of the system and due to the increased strength that develops in saturated dilative sands when negative pore pressures develop. Local bearing failure mechanism is observed in all saturated simulations. Finally, numerical CPT (quasi-static) and FFP tests were used to examine the strain rate coefficient used in practice (K); and a consistent range between 1 to 1.5 was obtained. / Master of Science / Accurate characterization of seabed sediments is crucial to understand sediment mobilization processes and to solve nearshore engineering problems such as scouring around offshore structures. Its portability, low testing effort, and repeatability make FreeFall Penetrometer (FFP) testing a highly cost-effective sediment characterization test. Nevertheless, due to the complex penetration mechanism of FFPs in soils (e.g., high-strain rate effects due to rapid FFP loading), converting FFP output into practical information is complicated, and it heavily relies on empirical correlations. This thesis presents a numerical analysis of FFP testing on saturated sand using the Material Point Method. First, the simulation results were compared with laboratory tests. Later, a parametric study was performed to understand the effect of different material parameters on the FFP response and to highlight in a simplified manner the effects of rapid loading on the sand behavior. Additional simulations in dry sand (without water) revealed that dry conditions provide larger FFP penetrations than saturated ones for the same material parameters. Lastly, the strain rate coefficient, which is a parameter required in one of the most common empirical methods for converting FFP output into geotechnical parameters, was back-calculated. The results were consistent with values used in practice for similar conditions.

Geotechnical sediment properties such as moisture content, relative density, bearing capacity, and undrained shear strength have been discussed in the context of coastal sediment dynamics. However, these properties have rarely been assessed in their respective relevance or quantitatively related to sediment transport and erodibility. Also, to date there is no framework available for collecting direct measurements of these properties for estimating initiation of motion and erosion rates. Here, it is postulated that improving the ability to measure geotechnical sediment properties in energetic foreshore environments can improve our ability to predict coastal response to climate change. Through a series of field measurements, the research presented here (1) provides a framework for conducting geotechnical measurements of beaches, (2) advances portable free fall penetrometer (PFFP) data analysis in intertidal environments through the introduction of an impact velocity dependent strain-rate correction factor, (3) relates textural and sediment strength properties derived from PFFP measurements to an erosion rate parameter and hydrodynamically driven bed-level change, and (4) uses PFFP measurements to develop a sediment classification scheme in terms of soil behavior and erosion behavior for a mixed sediment type Arctic environment. Relationships between sediment properties other than grain size, most significantly void ratio, and erodibility parameters highlight the relevance of these measurements in geomorphodynamically active sandy beach environments. For the cohesive sediments in the Arctic, undrained shear strength was also related to an erosion rate parameter, allowing for a categorical framework for erodibility classification to be developed. The cohesive framework was combined with the relationships developed for sandy sediments and used to highlight areas of active sediment transport in the context of local morphodynamic and ice gouging processes. Finally, a simple case study showed how implementing in-situ erodibility parameters was important for long-term morphological modelling. The results represent a step forward in our ability to predict and mitigate climate change related issues from coastal erosion. / Doctor of Philosophy / Climate change driven impacts on coastal environments include increasing frequency and severity of storms, coastal erosion, and inundation of populated areas. Specifically for Arctic environments, warming has caused more sediment to be introduced into coastal waters as well as accelerated rates of permafrost melting and shoreline retreat and decreases in sea ice. One aspect of understanding how these changes will continue to affect coastal communities and our ability to predict climate change effects is understanding the role of sediment properties on sediment erosion and shoreline change. Physical and geomechanical (strength) properties of coastal sediments are important for a variety of coastal applications but have rarely been investigated in the context of quantifying, predicting, and assessing erosion, specifically in the context of field measurements. Towards this end, a series of field surveys were conducted along the coast of North Carolina at a sandy beach, and in Harrison Bay, Alaska, an Arctic coastal zone with both sandy and muddy sediments. Tools for taking physical samples of the beach and seabed, measuring the sediment strength, among other properties in place were used to characterize the local sediments. Once a framework was developed for characterizing the type of sediment, the measured properties were then related to measurements of erosion rate from a series of laboratory experiments performed on physical samples taken from the sites. Finally, one of the instruments for measuring sediment strength both on land and in the water was used to develop classification schemes for seabed sediments in terms of their erodibility. The results of this work highlight the importance of geotechnical properties for coastal sediment transport processes, reveal new relationships between sediment properties and properties quantifying erosion behavior, and offer a framework for future research to classify erodibility of coastal environments in the field with a single piece of equipment. Overall, the work presented here contributes to our ability to measure, quantify, and predict coastal response to climate change.

Seabed surface sediments vary with active geomorphodynamics and sediment remobilization processes. Understanding relations between geotechnical sediment properties and sediment mobilization processes can potentially improve predictions of coastal erosion and hazard mitigation. Portable free fall penetrometers have emerged as an economic and useful tool for rapid geotechnical site characterization and uppermost sediment layer investigation. Acoustic methods have been used to assess seabed layering, scour evolution, and seabed morphology. However, there still exist major limitations in using these methods for classification and characterization of seabed sediment surface layers in the context of local sediment dynamics. Therefore, the goal of this research is to advance field data collection methods and field data availability towards advancing the current understanding and prediction of nearshore sediment dynamics. Geotechnical and geophysical measurements were conducted at different sites: Delaware Bay, Delaware; Pea Island, North Carolina; York River, Virginia; Potomac River, Maryland; Guadalupe River, Brazos River, Colorado River, Texas with different soil types and properties, hydrodynamic conditions, and morphological settings. The data collected was utilized to address the research goals through: (1) combining geotechnical and acoustic measurements to get better insight on sediment dynamics and erodibility, (2) proposing a framework that utilizes PFFP data to classify soil and estimate certain sediment properties (relative density and friction angle for sand and undrained shear strength for clays), relevant for local sediment dynamics, and (3) investigating how relevant geotechnical properties are reflected in acoustic, and specifically chirp sonar measurements. The findings of this research support the capability of portable free fall penetrometer to estimate sediment properties in topmost layers for different soil types such as friction angles, with an accuracy of ± 1° and undrained shear strength values, with <10% mismatches. Geoacoustic parameters such as acoustic impedance can also be calculated from acoustic measurements and correlated to certain sediment properties such as porosity and bulk density. Combining both measurements can yield better site characterization and accurate estimation of sediment properties for a better prediction of sediment dynamics. / Doctor of Philosophy / As the impacts of climate change seem to worsen, the likelihood of extreme events increases. This includes more frequent and severe events such as erosion, storm surges, melting glaciers, and sea level rise that impacts coastlines and coastal infrastructure. The increase in water levels increases the frequency of coastal hazards and flooding. These events result in devastating consequences, economically and environmentally, and disrupt people's lives all over the world. To adapt and reduce the severity of these consequences, there is a need to capture the changes in seabed, and a better understanding of seabed properties and their erodibility. This requires a reliable site characterization and an accurate estimate of seabed properties, which remain a challenge for different marine environments. There exist different site investigation methods to estimate seabed sediment properties that fall under geotechnical or geophysical types. One of the common geotechnical methods is a Portable free fall penetrometer (PFFPs), that presents a robust and economical tool for a rapid site assessment of topmost seabed layers. Geophysical tools, and mainly acoustic methods, are also often used to complement geotechnical methods due to their ability to cover vast areas in efficient time. However, both methods still face limitations in assessing seabed layers and properties. Therefore, the objective of this research is to develop a framework that paves the way for a reliable assessment of seabed properties using geotechnical and geophysical methods. Both methods were utilized for data collection in different locations across the US: Delaware Bay, Delaware; Pea Island, North Carolina; York River, Virginia; Potomac River, Maryland. Three additional sites Guadalupe, Brazos River, and Colorado Rivers, Texas were surveyed post hurricane Harvey that resulted in extreme flooding events. The measurements are collected from different coastal environments. This better account for the diversity in seabed to achieve a more generalized and well-integrated methodology to assess seabed layers under different conditions.

Dissertação(mestrado) - Universidade Federal do Rio Grande, Programa de Pós-Graduação em Engenharia Oceânica, Escola de Engenharia, 2010. / Submitted by Lilian M. Silva (lilianmadeirasilva@hotmail.com) on 2013-04-15T00:06:33Z No. of bitstreams: 1 baldez,a.l.pdf: 8426528 bytes, checksum: 47e41efbe0e6ba9d1074f9667287d13a (MD5) / Approved for entry into archive by Bruna Vieira(bruninha_vieira@ibest.com.br) on 2013-06-10T18:46:55Z (GMT) No. of bitstreams: 1 baldez,a.l.pdf: 8426528 bytes, checksum: 47e41efbe0e6ba9d1074f9667287d13a (MD5) / Made available in DSpace on 2013-06-10T18:46:55Z (GMT). No. of bitstreams: 1 baldez,a.l.pdf: 8426528 bytes, checksum: 47e41efbe0e6ba9d1074f9667287d13a (MD5) Previous issue date: 2010 / Este trabalho tem por objetivo o desenvolvimento, construção e testes preliminares de um penetrômetro de queda livre para a caracterização de solos marinhos. O aparelho tem por finalidade medir as características de resistência do solo oceânico, através da medição e analise da desaceleração imposta ao penetrômetro após o seu impacto com o fundo. Este tipo de equipamento evita os elevados custos envolvidos em outros tipos de ensaios e na obtenção de amostras do fundo em condições de elevado risco e dificuldades naturais impostas pelas condições locais do mar. O dispositivo tem o formato de um aerofólio Joukowski simétrico (formato de gota), que consiste de duas partes: a primeira onde fica o acelerômetro e o chumbo granulado e a segunda onde há um conector que liga o acelerômetro a um cabo de dados e daí a um computador portátil que realiza a aquisição de dados. O penetrômetro pode ser lançado de certa altura acima da superfície da água, entra na água e mobiliza resistência hidrodinâmica durante a queda livre. Após choca-se contra o fundo marinho mobilizando resistências ao cisalhamento do solo sendo desacelerado até o repouso. Para os testes de funcionamento do equipamento foi utilizada a marina do Rio Grande Yacht Club localizado na cidade de Rio Grande - RS. Nos testes foram obtidos sinais de desaceleração registrados pelo acelerômetro que foram integrados numericamente duas vezes, a primeira obtendo dados de velocidade e na segunda dados de deslocamento percorrido pelo penetrômetro. Os dados assim coletados permitiram uma estimativa do perfil de resistência ao cisalhamento do solo marinho ao longo do comprimento penetrado,observando que o penetrômetro adquiriu a velocidade terminal sendo mensurada em torno de 5,7 m/s e o deslocamento máximo registrado obtido na marina foi de 5 metros. / This study aims at developing, constructing and testing a free fall penetrometer for the characterization of marine soils. The objective of this device is to measure the strength characteristics of the marine soil, through the measurement and the analysis of the deceleration imposed by its impact on the bottom.This kind of equipment reduces high costs involved in other tests and in the collection ofsamples on the bottom under bad sea conditions regarding risks and natural obstacles. The device was shaped as a symmetric Joukowski airfoil (the shape of a drop) which consists of two parts: one of them holds the accelerometer and the granulated lead and the other one has a connector that links the accelerometer to a data cable, and then, to a portable computer which collects the data. The penetrometer can be launched from a certain height above the water surface, and then penetrates into the water and mobilizes hydrodynamic resistance during the free fall. When it hits the bottom of the sea, it mobilizes shear strength and decelerates until it rests. The tests with the equipment were carried out in the marina at the Rio Grande Yacht Club located in Rio Grande, RS, Brazil. The tests got deceleration signals which wererecorded by the accelerometer and were integrated twice numerically in order to collectdata on the velocity and on the displacement of the penetrometer. These data enabled the estimate of the shear strength profile of the marine soil along the length in which penetration occurred. The datashow that the velocity of the penetrometer reached about 5.7 m/s and thatthe maximum displacement recorded in the marina was 5 meters.