付記する学位プログラム名: グローバル生存学大学院連携プログラム / 京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21056号 / 工博第4420号 / 新制||工||1687(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 寶 馨, 教授 角 哲也, 准教授 佐山 敬洋 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

[pt] O tempo não produtivo (NPT) durante a perfuração de poços de petróleo pode ser responsável pela perda de milhões de dólares em atividades offshore. A má previsão da pressão de poros pode ser uma das responsáveis pelo NPT de um poço ou mesmo sua perda definitiva em campos geologicamente complexos, como em bacias evaporíticas. Nesses campos complexos, os métodos de previsão de pressão de poros convencionais nem sempre são capazes de prever bem a distribuição de pressão de poros, mesmo após a perfuração de número considerável de poços. Este trabalho estuda técnicas alternativas que atendam ao problema de previsão de pressão para esses casos. Para fundamentar os estudos, é apresentada uma revisão sobre os riscos associados à perfuração em bacias evaporíticas e sobre os métodos de previsão de pressão existentes (métodos convencionais, sísmicos, modelagem geológica geomecânica 3D, modelagem pelo método dos elementos finitos e modelagem de bacias). Avaliando os problemas de perfuração nestes campos e as dificuldades de previsão dos métodos convencionais, nota-se que a complexidade imposta pelas consequências da presença do sal pode ser reduzida pelo uso de métodos que considerem a geologia local de forma mais abrangente em seu fluxo de trabalho. Concluiu-se que a modelagem de bacias e a modelagem geológica geomecânica 3D têm forte potencial de aplicação para estes casos. As técnicas, contudo, não tem a previsão de pressão de poros por objetivo principal, mas podem ser aplicadas ou adaptadas para tal fim. Este estudo apresenta adaptações de metodologia e/ou aplicações direcionadas de ambas para fins de previsão de pressão de poros. Para validar as propostas apresentadas, estudos de caso foram desenvolvidos e apresentaram resultados considerados bastante satisfatórios. / [en] The non-productive time (NPT) while drilling oil and gas wells may be responsible for losing millions of dollars, especially in offshore activities. Bad pore pressure predictions may be responsible for large NPT or even the definitive loss of well in geologically complex fields, such as evaporate basins. On these complex fields, the conventional pore pressure prediction methods sometimes are not capable of providing good predictions, even if a considerable number of wells has been already drilled. This thesis studies alternative techniques which may attend for pore pressure prediction in these cases. In order to develop a consistent knowledge about the case, a literature review has been conducted in two ways: to understand what are the risks associated to drilling in evaporate basins; to review what are the available methods for pore pressure prediction (conventional methods, seismic methods, 3D geological and geomechanical modeling, finite element methods and basin modeling). During analyzing geomechanical drilling risks in these sites, and the difficulties found by conventional methods to predict it, it was noted that the complexity imposed by the presence of salt bodies can be reduced by using methods that make a strong use of geological knowledge on their workflow. It has been concluded that basin modeling and 3D geological and geomechanical modeling have a good potential to be applied for this goal. The techniques, nevertheless, do not have pore pressure prediction as their main goal, but can be applied to or adapted for such finality. This work presents some methodology adaptations and/or applications of both of techniques directed to pore pressure prediction goals. In order to validate the presented proposals, case studies has been developed, and their results were considered satisfactory.

[pt] O objetivo deste trabalho foi o de verificar a influência da modificação no campo de tensões ao redor de uma escavação em um maciço rochoso fraturado, observando a ocorrência do fechamento de fraturas e a redução da condutividade hidráulica na região ao redor da escavação. São apresentadas inicialmente as características básicas que devem ser consideradas ao analisar problemas em maciços rochosos fraturados e apontados os possíveis efeitos de uma escavação neste tipo de material. Uma breve revisão bibliográfica mostra alguns tipos de técnicas de análises numéricas disponíveis para simulação de problemas em meios descontínuos, com ênfase no método dos elementos discretos e, em especial, no método dos elementos distintos (DEM), empregado no software UDEC da Itasca Consulting Group Inc., utilizado neste trabalho. As simulações utilizam um acoplamento hidromecânico, onde o maciço é representado por um conjunto de blocos e as descontinuidades são tratadas como contornos dos blocos, sendo o fluxo permitido apenas no interior das fraturas. Foi utilizado um modelo hipotético com escavação circular para validação da modelagem a partir de soluções analíticas presentes na literatura. Além disso, foi realizado um estudo de caso real, de dois túneis localizados em uma importante via na cidade do Rio de Janeiro. A análise paramétrica do problema mostra a influência da modificação de algumas variáveis importantes neste tipo de fenômeno. Por fim, foram analisados os resultados de todos os casos, com suas considerações finais e sugestões para trabalhos futuros. / [en] This work aims to verify the influence of the stress field changing around an excavation in a jointed rock mass, noticing the fracture closure and the hydraulic conductivity decrease in the region surrounding the excavation. At first, the basic characteristics that should be considered in jointed rock masses analyses are presented, pointing out the potential effects caused by excavations in such materials. A brief literature review presents some types of numerical analysis techniques available for discontinuous medium modeling, focusing on the discrete elements methods and, specifically, in the distinct element method (DEM), applied in the UDEC software by Itasca Consulting Group Inc., which was utilized in this work. The simulations make use of a hydromechanical coupling, being the rock mass represented by an assembly of blocks. The water flow takes place among the discontinuities, which are treated as blocks’ boundaries. A hypothetical model was used for modeling validation by comparison with analytical solutions from the literature. Besides that, it was accomplished a real case study of two tunnels located at an important road in Rio de Janeiro city. The parametric analyses of the problem show the influence of changing some important variables in this type of phenomenon. At last, all the results have been discussed, with final considerations and future works suggestions.

Overpressure, or abnormally low effective pressures, is hazardous in drilling operations and construction of sea-bottom facilities in deepwater environments. Estimation of the locations of overpressure can improve safety in these operations and significantly reduce overall project costs. Propagation velocities of both seismic P and S wave are sensitive to bulk elastic parameters and density of the sediments, which can be related to porosity, pore fluid content, lithology, and effective pressures. Overpressured areas can be analyzed using 4C seismic reflection data, which includes P-P and P-SV reflections. In this thesis, the effects on compressional (P) and shear (S) wave velocities are investigated to estimate the magnitude and location of excess pore pressure utilizing Eaton’s approach for pressure prediction (Eaton, 1969). Eaton’s (1969) method relates changes in pore pressure to changes in seismic P-wave velocity. The underlying assumption of this method utilizes the ratio of observed P-wave velocity obtained from areas of both normal and abnormal pressure. This velocity ratio evaluated through an empirically determined exponent is then related to the ratio of effective stress under normal and abnormal pressure conditions. Effective stress in a normal pressured condition is greater than the effective stress value in abnormally overpressured conditions. Due to an increased sensitivity of variations in effective pressure to seismic interval velocity, Ebrom et al. (2003) employ a modified Eaton equation to incorporate the S-wave velocity in pore pressure prediction. The data preparation and subsequent observations of seismic P and S wave velocity estimates in this thesis represent a preliminary analysis for pore pressure prediction. Six 2D receiver gathers in the regional dip direction are extracted from six individual ocean-bottom 4C seismic recording nodes for P-P and P-SV velocity analysis. The receiver gathers employed have minimal pre-processing procedures applied. The main processing steps applied were: water bottom mute, 2D rotation of horizontal components to SV and SH orientation, deconvolution, and frequency filtering. Most the processing was performed in Matlab with a volume of scripts designed by research scientists from the University of Texas, Bureau of Economic Geology. In this thesis, fluid pressure prediction is estimated utilizing several 4C multicomponent ocean-bottom nodes in the Atlantis Field in deepwater Gulf of Mexico. Velocity analysis is performed through a ray tracing approach utilizing P-P and P-SV registration. A modified Eaton’s Algorithm is then used for pore pressure prediction using both P and S wave velocity values. I was able to successfully observe both compressional and shear wave velocities to sediment depths of approximately 800 m below the seafloor. Using Hamilton (1972, 1976) and Eberhart-Phillips et al. (1989) regressions as background depth dependent velocity values and well-log derived background effective pressure values from deepwater Gulf of Mexico, I am able to solve for predicted effective pressure for the study area. The results show that the Atlantis subsurface study area experiences a degree of overpressure. / text

La partie ouest du rift de Corinthe, en Grèce, s'ouvre à une vitesse d'environ 15 mm par an générant un taux de déformation parmi les plus élevés au monde, quelques séismes destructeurs de magnitude M>6 par décennie, et une forte activité microsismique irrégulière spatialement et temporellement. Afin de mieux comprendre les mécanismes liés à cette déformation crustale et de préciser les structures majeures actives, ce travail de recherche exploite la base de données sismologiques du Corinth Rift Laboratory de 2000 à 2015 en analysant finement les microséismes et leur évolution spatio-temporelle. La relocalisation globale des sources sismiques ainsi que leur classification en multiplets ont permis de préciser la géométrie des failles et d'identifier des comportements mécaniques différents. La zone ouest, au milieu du golfe, est affectée par des variations de pressions de fluides dans une couche géologique, entraînant des migrations des essaims de microséismes à des vitesses d'environ 50 m par jour. Les multiplets profonds de la partie centrale, près de la côte nord, sont persistants et semblent déclenchés par des épisodes de glissements lents asismiques sur un détachement immature pouvant atteindre la croûte ductile. Le faible pourcentage de déclenchement dynamique par les ondes sismiques suggère que l'état global du système de failles n'est pas au seuil critique de rupture. La magnitude des séismes est corrélée à l'impulsivité initiale de la rupture. Ces résultats précisent la dynamique de déformation du rift, les interactions sismique-asismiques, et permettront d'améliorer les modèles d'aléas sismiques de la région / The western part of the Corinth Rift in Greece is opening at about 15 mm per year, generating one of the highest deformation rates in the world, some destructive earthquakes of magnitude M>6 per decade, and high microseismic activity irregular in space and time. In order to better understand the mechanisms related to this crustal deformation and to specify the major active structures, this research work makes use of the seismological database of the Corinth Rift Laboratory from 2000 to 2015 by finely analyzing microearthquakes and their spatio-temporal evolution. The global relocation of the seismic sources and their classification into multiplets enable to refine the geometry of the faults and to identify different mechanical behaviors. The western zone, in the middle of the gulf, is affected by fluctuations of fluid pore pressures in a geological layer, resulting in microseismic swarm migrations at a velocity of about 50 m per day. The deep multiplets of the central part, near the northern coast, are persistent and appear to be triggered by episodes of slow aseismic slip along an immature detachment, which can reach the ductile crust. The low percentage of dynamic triggering by passing seismic waves suggests that the overall state of the fault system is not at the critical breaking point. The magnitude of earthquakes is correlated with the initial impulsiveness of the rupture. These results specify the dynamics of the rift deformation, the seismic-aseismic interactions, and will make possible the improvement of the seismic hazard models of the region

Master of Engineering (Research) / Soil surrounding a submarine buried pipeline consolidates as ocean waves propagate over the seabed surface. Conventional models for the analysis of soil behaviour near the pipeline assume a two-dimensional interaction problem between waves, the seabed soil, and the structure. In other words, it is often considered that water waves travel normal to the orientation of pipeline. However, the real ocean environment is three-dimensional and waves approach the structure from various directions. It is therefore the key objective of the present research to study the seabed behaviour in the vicinity of marine pipelines from a three-dimensional point of view. A three-dimensional numerical model is developed based on the Finite Element Method to analyse the so-called momentary behaviour of soil under the wave loading. In this model, the pipeline is assumed to be rigid and anchored within a rigid impervious trench. A non-slip condition is considered to exist between the pipe and the surrounding soil. Quasi-static soil consolidation equations are then solved with the aid of the proposed FE model. In this analysis, the seabed behaviour is assumed to be linear elastic with the soil strains remaining small. The influence of wave obliquity on seabed responses, i.e. the pore pressure and soil stresses, are then studied. It is revealed that three-dimensional characteristics systematically affect the distribution of soil response around the circumference of the underwater pipeline. Numerical results suggest that the effect of wave obliquity on soil responses can be explained through the following two mechanisms: (i) geometry-based three-dimensional influences, and (ii) the formation of inversion nodes. Further, a parametric study is carried out to investigate the influence of soil, wave and pipeline properties on wave-associated pore pressure as well as principal effective and shear stresses within the porous bed, with the aid of proposed three-dimensional model. There is strong evidence in the literature that the failure of marine pipelines often stems from the instability of seabed soil close to this structure, rather than from construction deficiencies. The wave-induced seabed instability is either associated with the soil shear failure or the seabed liquefaction. Therefore, the developed three-dimensional FE model is used in this thesis to further investigate the instability of seabed soil in the presence of a pipeline. The widely-accepted criterion, which links the soil liquefaction to the wave-induced excess pressure is used herein to justify the seabed liquefaction. It should be pointed out that although the present analysis is only concerned with the momentary liquefaction of seabed soil, this study forms the basis for the three-dimensional analysis of liquefaction due to the residual mechanisms. The latter can be an important subject for future investigations. At the same time, a new concept is developed in this thesis to apply the dynamic component of soil stress angle to address the phenomenon of wave-associated soil shear failure. At this point, the influence of three-dimensionality on the potentials for seabed liquefaction and shear failure around the pipeline is investigated. Numerical simulations reveal that the wave obliquity may not notably affect the risk of liquefaction near the underwater pipeline. But, it significantly influences the potential for soil shear failure. Finally, the thesis proceeds to a parametric study on effects of wave, soil and pipeline characteristics on excess pore pressure and stress angle in the vicinity of the structure.

Master of Engineering (Research) / Soil surrounding a submarine buried pipeline consolidates as ocean waves propagate over the seabed surface. Conventional models for the analysis of soil behaviour near the pipeline assume a two-dimensional interaction problem between waves, the seabed soil, and the structure. In other words, it is often considered that water waves travel normal to the orientation of pipeline. However, the real ocean environment is three-dimensional and waves approach the structure from various directions. It is therefore the key objective of the present research to study the seabed behaviour in the vicinity of marine pipelines from a three-dimensional point of view. A three-dimensional numerical model is developed based on the Finite Element Method to analyse the so-called momentary behaviour of soil under the wave loading. In this model, the pipeline is assumed to be rigid and anchored within a rigid impervious trench. A non-slip condition is considered to exist between the pipe and the surrounding soil. Quasi-static soil consolidation equations are then solved with the aid of the proposed FE model. In this analysis, the seabed behaviour is assumed to be linear elastic with the soil strains remaining small. The influence of wave obliquity on seabed responses, i.e. the pore pressure and soil stresses, are then studied. It is revealed that three-dimensional characteristics systematically affect the distribution of soil response around the circumference of the underwater pipeline. Numerical results suggest that the effect of wave obliquity on soil responses can be explained through the following two mechanisms: (i) geometry-based three-dimensional influences, and (ii) the formation of inversion nodes. Further, a parametric study is carried out to investigate the influence of soil, wave and pipeline properties on wave-associated pore pressure as well as principal effective and shear stresses within the porous bed, with the aid of proposed three-dimensional model. There is strong evidence in the literature that the failure of marine pipelines often stems from the instability of seabed soil close to this structure, rather than from construction deficiencies. The wave-induced seabed instability is either associated with the soil shear failure or the seabed liquefaction. Therefore, the developed three-dimensional FE model is used in this thesis to further investigate the instability of seabed soil in the presence of a pipeline. The widely-accepted criterion, which links the soil liquefaction to the wave-induced excess pressure is used herein to justify the seabed liquefaction. It should be pointed out that although the present analysis is only concerned with the momentary liquefaction of seabed soil, this study forms the basis for the three-dimensional analysis of liquefaction due to the residual mechanisms. The latter can be an important subject for future investigations. At the same time, a new concept is developed in this thesis to apply the dynamic component of soil stress angle to address the phenomenon of wave-associated soil shear failure. At this point, the influence of three-dimensionality on the potentials for seabed liquefaction and shear failure around the pipeline is investigated. Numerical simulations reveal that the wave obliquity may not notably affect the risk of liquefaction near the underwater pipeline. But, it significantly influences the potential for soil shear failure. Finally, the thesis proceeds to a parametric study on effects of wave, soil and pipeline characteristics on excess pore pressure and stress angle in the vicinity of the structure.

L'étude du comportement du béton en température est un problème majeur qui vise in fine à évaluer le niveau de sécurité des structures sous des sollicitations thermiques sévères, lors d'incendies par exemple. Pour cela, de nombreux modèles sont développés dans un cadre de couplage thermo-hydro-mécanique (THM), pour prendre en compte les différents processus physico-chimiques et mécaniques mobilisés par ces sollicitations et conditionnant la stabilité du matériau béton.Cependant, ces modélisations ne prennent souvent pas en compte explicitement la nature hétérogène du matériau. En effet, le béton est un matériau constitué d'inclusions noyées dans une matrice cimentaire pouvant être schématisée comme un milieu poreux ouvert partiellement saturé en eau. Les inclusions sont caractérisées par leurs natures minéralogiques, leurs morphologies et leurs tailles classées en fuseaux granulaires. Cette hétérogénéité introduit une complexité supplémentaire : la nécessité de prendre en compte la microstructure pour quantifier l'effet de l'incompatibilité (thermique, hydrique et mécanique) inclusion-matrice sur le comportement THM du béton. Ce travail constitue une première avancée dans ce sens. A ce titre, une modélisation élément fini multi-échelle tridimensionnelle (3D) est développée permettant d'affecter des comportements spécifiques à la matrice et aux inclusions. Pour la matrice, siège des transports de masse dans son réseau poreux connecté, une approche thermo-hydrique à trois fluides (eau, vapeur et air sec) est adoptée et est couplée à une loi de comportement poro-mécanique endommageable. Les inclusions (granulats) sont considérées hydriquement inertes, une approche thermo-mécanique avec endommagement est alors retenue.Une analyse, par simulations numériques, des effets de la nature minéralogique des granulats (calcaires ou silico-calcaires) de leurs distributions et de leurs morphologies a été menée sur des configurations 2D et 3D. Les effets étudiés ont notamment concerné l'influence de ces paramètres sur les fluctuations locales des champs de température, de pression de gaz et d'endommagement au regard de la dispersion des mesures expérimentales. L'analyse est limitée à l'échelle mésoscopique, celle où les granulats de taille caractéristique supérieure à 5 mm sont considérés, le reste (stable et pâte de ciment) étant une matrice homogène. Enfin, cette analyse a mis en évidence le besoin de mettre en œuvre une approche expérimentale cohérente avec une analyse mutli-échelle, à la fois pour la caractérisation des propriétés (thermiques, hydriques et mécaniques) de chaque constituant et pour l'étude des évolutions des champs lors des changements d'échelles. Un protocole expérimental a été définit et des premiers résultats d'essais sont présentés et analysés au travers de résultats obtenus dans la partie modélisation / The investigation of the behavior of heated concrete is a major research topic which concerns the assessment of safety level of structures when exposed to high temperatures, for instance during a fire. For this purpose, several modeling approaches were developed within thermo-hydro-mechanical (THM) frameworks in order to take into account the involved physic-chemical and mechanical processes that affect stability of heated concrete. However, existing models often do note account explicitly for the heterogeneity of the material : concrete is composite material that may be schematized as an assembly of inclusions (aggregates) embedded in a cementitious matrix (cement paste). This latter may be described as a partially saturated open porous medium. The aggregates are characterized by their mineralogical nature together with their morphology and size distribution. The material heterogeneity bring an additional complexity : the need to take into account the microstructure in order to quantify the effect of matrix-inclusion thermal, hygral and mechanical incompatibilities on the THM behavior of concrete. This work is a first step in this direction. For this purpose, a three-dimensional (3D) multi-scale finite element model is developed. It allows affecting specific behaviors to matrix and inclusions. For the former, where mass transports occur within the connected porous network, a three-fluids approach (liquid water, vapor and dry air) is adopted and is coupled to a poro-mechanical damage based approach. For inclusions (aggregates) no hygral component arises a pure thermo-mechanical model is considered. The developed model is then used to investigate, either by 2D or 3D numerical simulations, effects of mineralogical nature, morphology and distribution of aggregates. Studied effects have mainly concerned the influence of these parameters on local fluctuations of simulated temperature, gas pressure and damage fields with regard to experimentally observed dispersion. The analysis is here limited to the mesoscale, at which only aggregates with a characteristic size above 5 mm are meshed while the remaining inclusions together with the cement paste are considered to be a homogeneous matrix. Finally, the numerical analysis carries out the need to perform an experimental campaign that is consistent with a multi-scale approach of the THM behavior of concrete : an experimental campaign that allows to identify thermal, hygral and mechanical properties of each concrete constituent and that permit to assess evolution of fields during upscalling. An experimental protocol is then elaborated for this purpose and some obtained results are presented and analyzed with regard to results obtained in the modeling part

Chapter 1-2:The Cassini RADAR mapper has imaged elevated blocks and mountains on Titan we term ‘ridges’. Two unresolved problems regarding Titan's surface are still debated: what is the origin of its ridges and was there tectonic activity on Titan? To understand the processes that produced the ridges, in this study, (1) we analyze the distribution and orientation of ridges through systematic geomorphologic mapping and (2) we compare the location of the ridges to a new global topographic map to explore the correlation between elevation and ridges and the implications for Titan's surface evolution. Globally, the orientation of ridges is nearly E-W and the ridges are more common near the equator than at the poles, which suggests a tectonic origin for most of the ridges on Titan. In addition, the ridges are found to preferentially lie at higher-than-average elevations near the equator. We conclude the most reasonable formation scenario for Titan's ridges is that contractional tectonism built the ridges and thickened the icy lithosphere, causing regional uplift. The combination of global and regional tectonic events, likely contractional in nature, plus enhanced fluvial erosion and sedimentation near the poles, would have contributed to shaping Titan's tectonic landforms and surface morphology to what we see today. However, contractional structures (i.e. thrusts and folds) require large stresses (8~10 MPa), the sources of which probably do not exist on Titan. Liquid hydrocarbons in Titan's near subsurface must play a role similar to that of water on Earth and lead to fluid overpressures, which enable contractional deformation at smaller stresses (< 1MPa) by significantly reducing the shear strength of materials. We show that crustal conditions with enhanced pore fluid pressures on Titan favor the formation of thrust faults and related folds, in a contractional stress field. The production of folds, as on Earth, is facilitated by the presence of crustal liquids to weaken the crust. These hydrocarbon fluids have played a key role in Titan's tectonic evolutionary history, leaving it the only icy body on which strong evidence for contractional tectonism exists. Chapter 3: Arthur Wichmann's ‘Earthquakes of the Indian Archipelago’ documents several large earthquakes and tsunami throughout the Banda Arc region that can be interpreted as mega-thrust events. However, the source regions of these events are not known. One of the largest and well-documented events in the catalog is the great earthquake and tsunami affecting the Banda islands on 1 August 1629. It caused severe damage from a 15-meter tsunami that arrived at the Banda Islands about a half hour after violent shaking stopped. The earthquake was also recorded 230 km away in Ambon, but no tsunami is mentioned. This event was followed by at least 9 years of uncommonly frequent seismic activity in the region that tapered off with time, which can be interpreted as aftershocks. The combination of these observations indicates that the earthquake was most likely a mega-thrust event. We use an inverse modeling approach to numerically reconstruct the tsunami, which constrains the likely location and magnitude of the 1629 earthquake. Only linear numerical models are applied due to the low-resolution of bathymetry in the Banda Islands and Ambon. Therefore, we apply various wave amplification factors (1.5 to 4) derived from simulations of recent, well-constrained tsunami to bracket the upper and lower limits of earthquake moment magnitudes for the event. The closest major earthquake sources to the Banda Islands are the Tanimbar and Seram Troughs of the Banda subduction/collision zone. Other source regions are too far away for such a short arrival time of the tsunami after shaking. Moment magnitudes predicted by the models in order to produce a 15 m tsunami are Mw of 9.8 to 9.2 on the Tanimbar Trough and Mw 8.8 to 8.2 on the Seram Trough. The arrival times of these waves are 58 minutes for Tanimbar Trough and 30 minutes for Seram Trough. The model also predicts 5 meters run-up for Ambon from a Tanimbar Trough source, which is inconsistent with the historical records. Ambon is mostly shielded from a wave generated by a Seram Trough Source.We conclude that the most likely source of the 1629 mega-thrust earthquake is the Seram Trough. Only one earthquake > Mw 8.0 is recorded instrumentally from the eastern Indonesia region although high rates of strain (50-80 mm/a) are measured across the Seram section of the Banda subduction zone. Enough strain has already accumulated since the last major historical event to produce an earthquake of similar size to the 1629 event. Due to the rapid population growth in coastal areas in this region, it is imperative that the most vulnerable coastal areas prepare accordingly.

Concrete buttress dams are relatively light structures and less demandingon foundations; because of that, they may have problems with upliftforces and horizontal joints in the area of the dam´s foundation maypresent a failure mode through sliding. The Storfinnforsen dam, thelargest concrete dam in Sweden, had its foundation studied recently andthe discovery of sub-horizontal joints in the bedrock led to the necessityof having the safety of the dam foundation to sliding assessed.The safety is dependent on the pore pressure, which can vary throughtime. The implementation of an alarm system to monitor and assess thevalues of the pore pressure is necessary to improve the dam´s operation.In this thesis, a new system on how to define alarm limits for measuredpore pressures is suggested.The proposed alarm system will monitor the pore pressure of the joint,calculate the safety factor against sliding, compare it to the alarm limits ofthe system (adopted from RIDAS) and present countermeasures to theproblem.The analysis and implementation of the alarm system on monolith 42 ofStorfinnforsen showed that it does not comply with the Swedishguidelines with respect to sliding stability, but the measured porepressures are low enough to allow the creation of an alarm system thatwill monitor the pore pressure continuously. Furthermore, thecharacteristics of the local geology exclude any quick development of porepressure allowing countermeasures to be applied.However, further research on the definition of alarm limits for this kindof problem is needed. / Lamelldammar av betong är relativt lätta konstruktioner med mindrepåkänningar på grunden jämfört med konventionellagravitationsdammar. Till följd av detta är de också känsliga för upptryck.I kombination med förekomsten av sub-horisontella sprickplan iberggrunden kan detta utgöra en risk för glidning. Vid Storfinnforsensbetongdamm, vilken är Sveriges största lamelldamm, har undersökningarav berggrunden genomförts. I samband med dessa undersökningaridentifierades sub-horisontella sprickplan i berggrunden ochmonoliternas glidstabilitet har därför analyserats med avseende påglidning. Dränage har även borrats och portrycksmätare installerats föratt övervaka portrycket i berggrunden.Portrycket, och därmed dammens säkerhet mot glidning, kan emellertidvariera över tid. Det är därför nödvändigt att utveckla och implementeraett alarmsystem för att övervaka portrycket och säkerställa dammenssäkerhet. I följande examensarbete har ett nytt system utvecklats för attdefiniera alarmgränser för uppmätta portryck. I det föreslagnaalarmsystemet övervakas portrycket över sprickplanen, säkerhetsfaktornmot glidning beräknas och jämförs mot gränser baserade på acceptablasäkerhetsfaktorer från RIDAS. Om uppmätta portryck överstigeralarmgränserna implementeras fördefinierade åtgärder.I detta arbete implementerades alarmsystemet på monolit 42 iStorfinnforsens lamelldamm. Resultaten från en inledandestabilitetsanalys visade att säkerhetsfaktorn mot glidning inte uppfyllerställda krav enligt RIDAS riktlinjer. De uppmätta portrycken äremellertid tillräckligt låga för att möjliggöra användningen av ettalarmsystem som övervakar portrycken kontinuerligt och därmedsäkerställer att säkerheten mot glidning uppfylls. Om portrycken skulleöverstigas ges förslag på möjliga åtgärder som kan genomföras för attsänka portrycken. Vidare indikerar de lokala geologiska förhållandena attVsnabba höjningar av portrycken till följd av exempelvis urspolning avfyllnadsmaterial från sprickplan är osannolika, vilket möjliggörimplementering av de fördefinierade åtgärderna om portrycket skullestiga. Vidare forskning rekommenderas emellertid på hur snabbtportrycken kan stiga till följd av olika scenarier såsom nedbrytning avinjekteringsridåer.