In this study, The Beach Dewatering System, a relatively recent technology to combat beach erosion, which is proposed as a practical alternative to more traditional shoreline stabilization methods, is investigated and an informative overview on the genesis, development and recent use of this technique is provided. On the basis of the link existing between the elevation of beach groundwater and erosional or accretionary trends at the beach face, a numerical model that simulates groundwater flow in a coastal aquifer under beach drainage is presented. In this model, the seaward boundary of the domain is considered to be tidally fluctuating in a large scale to represent the occurrence of seepage face significantly. The unsteady groundwater flow equation is solved numerically using the method of finite differences. The results clearly showed that the water table being lowered caused the reduction of the seepage face which is the main aim of Beach Dewatering projects. The positional design parameters, i.e. horizontal and vertical location of the drain, are also investigated by utilizing an efficiency index. It is observed that the system efficiency decreased as the drain is shifted landward. The results also indicated that, the efficiency slightly increased with the vertical drain elevation.

A quantitative understanding of ground water flow characteristics in unconfined aquifers is important because of the prevalence of abstraction from, and pollution of these systems. The current understanding of ground water flow in unconfined aquifers is limited because of the dominance of horizontal flow modelling strategies used to represent unconfined flow processes. The application of horizontal flow principles leads to an ignorance of seepage-face formation and can not predict the complicated three-dimensional nature of the ground water flow that dominates at the ground water-surface water interface. This study aims to address some of these deficiencies by exploring the true three-dimensional nature of ground water flow including the formation of seepage faces at the ground water-surface water interface using numerical and laboratory techniques. A finite element model for simulating two-dimensional (vertical) variably saturated flow is developed and benchmarked against standard laboratory and field-scale solutions. The numerical features of the finite element model are explored and compared to a simple finite difference formulation. The comparison demonstrates how finite element formulations lead to a broader spatial averaging of material properties and a different method for the representation of specified flux boundaries. A detailed comparison analysis indicates that these differences in the finite element solution lead to an improved approximation to the partial differential equation governing two-dimensional (vertical) variably saturated flow. A laboratory analysis of unconfined ground water flow and associated solute transport characteristics was performed. The analysis focused upon unconfined flow towards a pumping well. The laboratory observations were reliably reproduced using a three-dimensional (axi-symmetric), variably saturated ground water flow model. The model was benchmarked against the ground water flow characteristics such as the seepage-face height and total flow rate. In addition, the model was shown to reliably reproduce the solute transport features such as travel times and streamline distributions. This is the first time that a numerical model has been used to reliably reproduce the solute transport characteristics near a seepage-face boundary where the three-dimensional flow effects are prevalent. The ability to reliably predict solute transport patterns in the seepage-face zone is important since this region is known to support vital microbially facilitated reactions that control nutrient cycling and contaminant attenuation. The three-dimensional travel time distribution near the seepage-face was compared to that predicted using a horizontal flow modelling approach derived from the basic Dupuit-Forchheimer equations. The Dupuit-Forchheimer based model indicated that horizontal flow modelling would under-estimate the total residence time near a seepage-face boundary, thereby introducing a considerable source of error in a solute transport analysis. For this analysis, a new analytical solution for the steady travel time distribution in an unconfined aquifer subject to a single pumping well was derived. The analytical model has identified, for the first time in the hydrogeology literature, the use of the imaginary error function. The imaginary error function is a standard transcendental function and an infinite series approach to evaluate the function was successfully proposed. The two-dimensional (vertical) ground water flow model was extended to handle the case where the flow is driven by density gradients near the ground water-surface water interface. The unsteady, two-dimensional, Galerkin finite element model of density-dependent ground water flow in variably saturated porous media is rigorously presented and partially benchmarked under fully saturated (confined) conditions. The partial benchmarking involved reproducing solutions to the standard Henry salt-water intrusion and the Elder salt-convection problems. The model was used in a standard density-coupled and a new density-uncoupled mode to elucidate the worthiness of the Henry and Elder problems as benchmark standards. A comparison of the coupled and uncoupled solutions indicates that the Henry salt-water intrusion problem has limited worthiness as a benchmark as the patterns of ground water flow are relatively insensitive to density-coupled effects. Alternatively, the Elder problem is completely dependent upon a correct representation of the density-coupled flow and solute transport processes. The coupled versus uncoupled comparison is proposed as a new test of the worthiness of benchmark standards. The Henry salt-water intrusion problem was further analysed in an attempt to alleviate some of the difficulties associated with this benchmark problem. The numerical model was tested against a re-evaluated version of Henry's semi-analytical solution for the coupled solute concentration distribution. The numerical model was used to propose a modified version of the Henry problem where the importance of density-coupled processes was increased. The modified problem was shown to have an improved worthiness as compared to the standard solution. The numerical model results were benchmarked against a new set of semi-analytical results for the modified problem. Certain advantages in using the modified problem as a test case for benchmarking the results of a numerical model of density-dependent ground water flow are identified. A numerical investigation of the patterns of density-driven ground water flow at the ground water-surface water interface was undertaken. The numerical model is shown to produce grid-independent results for a finely discretised domain. The pattern of discharge is controlled, in part, by two parameters. One describes the recharge applied to the aquifer, and the second describes the magnitude of the density differences between the fresh recharging fluid and the saline receiving fluid. The influence of dense intrusions upon the formation of seepage-face boundaries at the ground water-surface water interface under steady-state conditions was also investigated. Dense intrusions are shown to dominate the pattern of ground water flow only under mild recharge conditions, while seepage faces dominate the outflow pattern under strong recharge conditions. Therefore, the formation of seepage-face boundaries and dense intrusions are unlikely to coincide under the conditions examined in this study.

O conhecimento de zonas potencialmente instáveis no fundo do mar é de fundamental importância para o desenvolvimento das estruturas marinhas, pois permite posicionar estruturas offshore em áreas mais seguras, reduzindo-se possíveis danos, custos e eventual poluição ambiental. Nesse contexto, o objetivo do presente trabalho é investigar, através de uma abordagem analítico-numérica, a estabilidade de maciços submarinos submetidos ao carregamento cíclico da onda. O efeito das ondas de água sobre o leito submerso é descrito pela propagação de uma onda de pressão ao longo de sua superfície, empregando-se a teoria linear de Stokes. São considerados maciços com superfície superior horizontal e inclinada, constituídos por material coesivo (argilas) e material granular (areias). Em maciços constituídos por solos finos, a capacidade resistente do material é modelada pelo critério de Tresca não-homogêneo e a análise da estabilidade é desenvolvida em condição não drenada. Por outro lado, em leitos granulares, a resistência do meio depende explicitamente do valor da poropressão, sendo descrita classicamente pelo critério de Coulomb sem coesão. A análise de estabilidade é então desenvolvida em tensões efetivas e o gradiente de poropressão atua como uma força volumétrica sobre o esqueleto, caracterizando o modo de carregamento principal deste material. Em razão da tendência a se densificar quando submetido a um estado de tensões desviadoras cíclicas, ocorre, em geral, a acumulação de excesso de poropressão no maciço granular. Consequentemente, o acoplamento entre o comportamento do material e o carregamento cíclico tem fundamental importância sobre o cálculo do excesso de poropressão desenvolvido. Para determinação das forças de percolação, considera-se uma abordagem simplificada baseada na partição das deformações em contribuições reversível e irreversível, que permite desacoplar o cálculo da pressão intersticial induzida pela onda. Aplicando-se conceitos da teoria da Análise Limite é possível formular limites inferiores e superiores da máxima amplitude segura do carregamento da onda. Finalmente, os efeitos da declividade da superfície do leito e da espessura de camada de solo sobre a estabilidade são analisados. / The knowledge of potentially unstable areas on the seabed is of fundamental importance to the development of marine structures, because it allows to install offshore structures in safer areas, reducing possible damages, costs and eventual environmental pollution. In this context, the objective of the present work is to investigate the stability of submarine soil masses subjected to the wave cyclic loading through analytical-numerical approaches. The effect of water waves on the submerged bed is described by the propagation of a pressure wave along its surface, using the Stokes’s linear theory. Soil masses with horizontal and sloped upper surface, composed of cohesive material (clays) and granular materiais (sands) are considered in this study. In soil masses constituted of fine soil, the material strength capacity is modeled by the non-homogeneous Tresca criterion and the stability analysis is carried out in undrained condition. On the other hand, in granular beds, the strength explicitly depends on the pore pressure value, being classically described by the Coulomb criterion without cohesion. Then, the stability analysis is developed in effective stress and the pore pressure gradient acts as a volumetric force on the skeleton, characterizing the main charging mode of this material. Due to the tendency to densify when subjected to a cyclic deviatoric stress state occurs, in general, the build-up of pore pressure excess in the granular mass. Consequently, the coupling between the material behavior and the cyclic loading has fundamental importance in the calculation of the pore pressure excess generated. In order to define the seepage forces, a simplified approach based on the partition of deformations in reversible and irreversible contributions is considered, which allows to decouple the wave-induced pore pressure calculation. Applying the concepts of the limit analysis theory it is possible to formulate upper and lower boundaries of the maximum safe amplitude of the wave loading. Finally, the effects of the seabed surface steepness and of the soil layer thickness on the stability are analyzed.

O conhecimento de zonas potencialmente instáveis no fundo do mar é de fundamental importância para o desenvolvimento das estruturas marinhas, pois permite posicionar estruturas offshore em áreas mais seguras, reduzindo-se possíveis danos, custos e eventual poluição ambiental. Nesse contexto, o objetivo do presente trabalho é investigar, através de uma abordagem analítico-numérica, a estabilidade de maciços submarinos submetidos ao carregamento cíclico da onda. O efeito das ondas de água sobre o leito submerso é descrito pela propagação de uma onda de pressão ao longo de sua superfície, empregando-se a teoria linear de Stokes. São considerados maciços com superfície superior horizontal e inclinada, constituídos por material coesivo (argilas) e material granular (areias). Em maciços constituídos por solos finos, a capacidade resistente do material é modelada pelo critério de Tresca não-homogêneo e a análise da estabilidade é desenvolvida em condição não drenada. Por outro lado, em leitos granulares, a resistência do meio depende explicitamente do valor da poropressão, sendo descrita classicamente pelo critério de Coulomb sem coesão. A análise de estabilidade é então desenvolvida em tensões efetivas e o gradiente de poropressão atua como uma força volumétrica sobre o esqueleto, caracterizando o modo de carregamento principal deste material. Em razão da tendência a se densificar quando submetido a um estado de tensões desviadoras cíclicas, ocorre, em geral, a acumulação de excesso de poropressão no maciço granular. Consequentemente, o acoplamento entre o comportamento do material e o carregamento cíclico tem fundamental importância sobre o cálculo do excesso de poropressão desenvolvido. Para determinação das forças de percolação, considera-se uma abordagem simplificada baseada na partição das deformações em contribuições reversível e irreversível, que permite desacoplar o cálculo da pressão intersticial induzida pela onda. Aplicando-se conceitos da teoria da Análise Limite é possível formular limites inferiores e superiores da máxima amplitude segura do carregamento da onda. Finalmente, os efeitos da declividade da superfície do leito e da espessura de camada de solo sobre a estabilidade são analisados. / The knowledge of potentially unstable areas on the seabed is of fundamental importance to the development of marine structures, because it allows to install offshore structures in safer areas, reducing possible damages, costs and eventual environmental pollution. In this context, the objective of the present work is to investigate the stability of submarine soil masses subjected to the wave cyclic loading through analytical-numerical approaches. The effect of water waves on the submerged bed is described by the propagation of a pressure wave along its surface, using the Stokes’s linear theory. Soil masses with horizontal and sloped upper surface, composed of cohesive material (clays) and granular materiais (sands) are considered in this study. In soil masses constituted of fine soil, the material strength capacity is modeled by the non-homogeneous Tresca criterion and the stability analysis is carried out in undrained condition. On the other hand, in granular beds, the strength explicitly depends on the pore pressure value, being classically described by the Coulomb criterion without cohesion. Then, the stability analysis is developed in effective stress and the pore pressure gradient acts as a volumetric force on the skeleton, characterizing the main charging mode of this material. Due to the tendency to densify when subjected to a cyclic deviatoric stress state occurs, in general, the build-up of pore pressure excess in the granular mass. Consequently, the coupling between the material behavior and the cyclic loading has fundamental importance in the calculation of the pore pressure excess generated. In order to define the seepage forces, a simplified approach based on the partition of deformations in reversible and irreversible contributions is considered, which allows to decouple the wave-induced pore pressure calculation. Applying the concepts of the limit analysis theory it is possible to formulate upper and lower boundaries of the maximum safe amplitude of the wave loading. Finally, the effects of the seabed surface steepness and of the soil layer thickness on the stability are analyzed.

This diploma thesis deals with the analysis of the monitoring of the Karolinka water reservoir earth dam. For the reason of seepage detected on the downstream face of the dam, the water reservoir was operated in a limited regime practically from its beginning. One of the most significant interventions aimed at reducing them was the installation of a sealing wall realized in 2013. Since 2011, the earth dam has been pilot-monitored by probes of the electrical impedance spectrometry method. The thesis deals with the processing of the data obtained by this method and with the comparison of the determined electrical conductivity of the dam soil with the data measured on the earth dam (temperature, water level in the reservoir, seepage) before and after installation of the sealing wall.

The main goal of this research is to quantitatively assess the resilience and vulnerability of geotechnical infrastructure to extreme events under a changing climate. In the first part, pertinent facts and statistics regarding California’s extreme drought and current status of its levees are presented. Weakening processes such as soil strength reduction, soil desiccation cracking, land subsidence and surface erosion, and oxidation of soil organic carbon are comprehensively evaluated to illustrate the devastating impacts that the California drought can have on earthen structures. In the second part, rainfall-triggered slope instabilities are analyzed using extreme precipitation estimates, derived using the historical stationary and a proposed future nonstationary approach. The extremes are integrated into a series of fully coupled 2D finite element simulations. The final part of this study investigates the impact of simultaneous variations in soil moisture and temperature changes in the California region on soil strength through a proposed thermo-hydro-mechanical framework.

Several hydraulic loadings impose earthen levees to time-dependent variably saturated seepage conditions. The main objective of this study is to improve the analysis of levees under transient seepage with the use of unsaturated soil mechanics. An extensive set of laboratory testing, field monitoring and numerical modeling are performed to analyze a silty sand setback levee located near Seattle, WA. In-situ data obtained from field monitoring are used to monitor suction and effective stress within the levee’s embankment and foundation over the past two years. Soil samples taken from the site are used to perform index, water retention, and unsaturated multi-stage triaxial tests in the laboratory. A finite element model of transient seepage under saturated-unsaturated conditions is then developed and calibrated to reasonably match the field data. The results highlight the need to consider unsaturated soil mechanics along with climatic variables and soil-atmosphere interaction when analyzing levees under transient seepage conditions.

The devastating levee failures associated with hurricanes Katrina and Rita, and the more recent Midwest flooding, placed a spotlight on the importance of levees and our dependence on them to protect life and property. In response to levee failures associated with the hurricanes, Congress passed the Water Resources Development Act of 2007 which established a National Committee on Levee Safety. The committee was charged with developing recommendations for a National Levee Safety Program. The Secretary of the Army was charged with the establishment and maintenance of a National Levee Database. The National Levee Database is a critical tool in assessing and improving the safety of the nation's levees. However, the NLD data model, established in 2007, lacked a structure to store seepage and slope stability analyses – vital information for assessing the safety of a levee. In response, the Levee Analyst was developed in 2008 by Dr. Norm Jones and Jeffrey Handy. The Levee Analysis Data Model was designed to provide a central location, compatible with the National Levee Database, for storing large amounts of levee seepage and slope stability analytical data. The original Levee Analyst geoprocessing tools were created to assist users in populating, managing, and analyzing Levee Analyst geodatabase data. In an effort to enhance the Levee Analyst and provide greater accessibility to levee data, this research expanded the Levee Analyst to include modifications to the data model and additional geoprocessing tools that archive GeoStudio SEEP/W and SLOPE/W simulations as well as export the entire Levee Analyst database to Google Earth. Case studies were performed to demonstrate the new geoprocessing tools' capabilities and the compatibility between the National Levee Database and the Levee Analyst database. A number of levee breaches were simulated to prototype the enhancement of the Levee Analyst to include additional feature classes, tables, and geoprocessing tools. This enhancement would allow Levee Analyst to manage, edit, and export two-dimensional levee breach scenarios.

Climate change results to more extreme and frequent flood events that induce extra risk to flood protection structures such as levees. Thus, estimation of the probability of levee failure is of utmost importance when it comes to structural safety and flood risk assessment. This master thesis focuses on the estimation of the probability of levee failure owing to backward erosion at the foundation of the levee. For the estimation of the probability of failure three breach models of different complexity were developed and site-specified data were used from the Paglia river area and an assessment of the results followed. Besides the breach models, a 2-D hydraulic model was also built where breach scenarios were used to assess the associated flood risk. The results showed that the complexity of the breach model plays significant role to the estimated probability of failure. The simplest model estimated the lowest probability, while the complex the highest. Consequently, the associated to the complex model flood risk was higher than the other two. / Klimatförändringarna är ett allmänt problem som bland annat resulterar i ökad risk för extrema hydrologiska händelser. Av dessa extrema händelser är översvämningar bland de mest förekommande. För att tackla problemen med översvämningsriskerna används skyddsvallar som en av de vanligaste anläggningarna bland olika översvämningsskydd. Vid ett tillräckligt högt flöde kan dock den ökade belastningen på skyddsvallen orsaka att skyddsvallen havererar. En skyddsvall kan haverera på grund av flera fysikaliska fenomen, varav de vanligaste är inre erosion, otillräcklig släntstabilitet samt överspolning. Risken för att en skyddsvall havererar, det vill säga brottrisken, kan beräknas med olika metoder. Sannolikhetsbaserade metoder har nyligen växt fram som ett allt viktigare tillvägagångssätt. Det här examensarbetet handlar om brottsannolikhetsberäkningar för skyddsvallar i syfte att kartlägga översvämningsrisker. Arbetet fokuserar på fenomenet med inre erosion i skyddsvallars grundläggning. Det praktiska exemplet i examensarbetet studerar nybyggda skyddsvallar utmed den italienska floden Paglia längs en flodsträcka om 4,5 km mellan städerna Ciconia och Orvieto Scalo i regionen Umbria i centrala Italien. Ur ett hydrogeologiskt perspektiv karaktäriseras regionen av fint jordmaterial, med inslag av slutna akviferer. Sannolikhetsberäkningar med hjälp av ramverket för Monte Carlo-analys genomfördes för tre olika modeller för att beskriva inre erosion i skyddsvallarna till följd av ett 200-årsflöde. De tre olika numeriska modellerna kännetecknades av olika grad av komplexitet. Den enklaste modellen baserades på en metod av Mazzoleni et al. (2015) och tog endast hänsyn till skyddsvallens porositet. Den mellankomplexa modellen var baserad på metoden ifrån Khilar et al. (1985). Den mest komplexa modellen var tidsberoende och baserades på metoderna från Sellmeijer et al. (2011) och Scheuermann (2005), för att ta hänsyn till de två ömsesidigt beroende fenomenen bakåterosion, så kallad ”piping” och läckage, så kallat ”seepage”, vilka tillsammans ger upphov till inre erosion. Resultaten visar att graden av komplexitet i den numeriska modellen spelar en viktig roll när det gäller brottsannolikheten för skyddsvallars grundläggning. Den enklaste modellen beräknade en lägre brottsannolikhet än de andra två modellerna, och den mest komplexa modellen beräknade högst brottsannolikhet av de tre modellerna. Vidare visar resultaten på att några parametrar har en stor inverkan på brottsannolikheten. Dessa är bland annat partikeldiametern som påverkar skjuvhållfastheten i materialet, permeabiliteten, jordlagrets tjocklek under skyddsvallen samt strömningsvaraktigheten. Parametern strömningsvaraktighet kan endast beaktas i tidsberoende modeller, vilket är en av fördelarna med den mest komplexa modellen i denna studie. Förutom de numeriska brottsannolikhetsmodellerna byggdes en tvådimensionell hydraulisk modell upp för att kartlägga de resulterande översvämningsriskerna. Tre olika haveriscenarier studerades för att representera de tre brottsannolikhetsmodellerna. Dock visade det sig att den enklaste av de tre modellerna beräknade så låg brottsannolikhet att det inte var meningsfullt att studera de resulterande översvämningsriskerna enligt den enklaste brottsannolikhetsmodellen i den hydrauliska modellen. Av de två mer komplexa brottsannolikhetsmodellerna visade det sig att den mest komplexa av de två gav mer omfattande haverier i skyddsvallarna och dessutom haverier i flera av skyddsvallarna. Vidare gav den mest komplexa modellen upphov till högst vattennivåer bakom de havererade skyddsvallarna. Slutligen kan det nämnas att staden Scalo Orvieto är utsatt för en högre översvämningsrisk än staden Ciconia enligt resultaten i denna studie.

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