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Empirical correlations between different geotechnical parameters are frequently sought after by exploiting multivariate databases. An example are estimations of total unit weight from cone penetration tests (CPTu), which are very useful in earlier design stages. If the underlying soil database includes data from many different soils a single correlation may lack precision. Precision is gained when the underlying database is narrowed down to some specific soil type, but the applicability of a soil-specific correlation is also limited. A way out of this dilemma is to apply clustering techniques to a general database before developing separate correlations for different clusters. Projecting the clustered data back to a convenient classification space (e.g., one spanned by normalized CPTu metrics) new data can be easily assigned to different clusters and the appropriate correlation used. This idea is illustrated here using Bayesian Mixture Analysis (BMA) to identify hidden soil classes within a general geotechnical database that supports correlations between soil total unit weight and CPTu readings. It is shown that BMA supported clustering improves the accuracy of previous regressions, and, more importantly, facilitates the formulation of novel and more accurate regressions. A simple discriminant criterion is developed to facilitate application of cluster-based regressions to new sites. The good performance of the method is illustrated with application to a deltaic site., This research received funding from the European Union's Horizon 2020 research and innovating programme under the Marie Sklodowska-Curie grant agreement No 721403. Financial support of Ministerio de Ciencia e Innovación of Spain through research project PID2020-119598RB-I00 is gratefully appreciated, Peer Reviewed, Postprint (published version)

Node-based smoothed finite element (NS-FEM) formulations for the coupled hydro-mechanical problem are now becoming popular in soil mechanics, but there has been limited comparative study of their performance. In this work, a node-based formulation is developed for the coupled hydro-mechanical problem (u-pw formulation) using low-order, equal-order interpolants and an implicit time marching scheme for the global problem. The numerical properties of the resulting formulation are then compared to different implementations of classical finite elements. The use of nodal smoothing does not render by itself the solution stable at the undrained limit, on the contrary, the range of undrained instability is increased. Stabilizing terms previously employed in FEM are equally successful in stabilizing NS-FEM solutions, but the computational cost of the stabilized solution is much higher for NS-FEM. It is also shown that NS-FEM does not present by itself any particular advantage in terms of mesh dependency over classic FEM: when strain localization is present the solution obtained is strongly dependent on mesh size., Financial support of Ministerio de Ciencia e Innovación of Spain (MCIN/AEI/10.13039/501100011033) through the Severo Ochoa Centre of Excellence project (CEX2018-000797-S) and research project PID2020-119598RB-I00 is gratefully appreciated., Peer Reviewed, Postprint (author's final draft)

Accurate estimates of soil unit weight are fundamental for correctly post process CPTu data and making use of Soil Behavior Type-based classification systems. Soil-specific and global regressions have been proposed for this purpose. However, soil-specific correlation might pose a problem of pertinence when applied at new sites. On the other hand, global correlations are easy to apply, but generally carry large systematic uncertainties. In this context, this work proposes a data clustering technique applied to geotechnical database aiming to identify hidden linear trends among dimensionless soil unit weight and normalized CPTu parameter according to some unobservable soil classes. Global correlations are then revisited according to such data subdivision aiming to improve accuracy of soil unit weight prediction while reducing transformation uncertainty. A new probabilistic criterion for soil unit weight prediction is also obtained. The potential benefits of the proposed procedure are illustrated with data from a Llobregat delta site (Spain)., Postprint (published version)

The task of geotechnical site characterization includes defining the layout of ground units and establishing their relevant engineering properties. This is an activity in which uncertainties of different nature (inherent, experimental, of interpretation…) are always present and in which the amount and characteristics of available data are highly variable. Probabilistic methodologies are applied to assess and manage uncertainties. A Bayesian perspective of probability, that roots probability on belief, is well suited for geotechnical characterization problems, as it has flexibility to handle different kind of uncertainties and highly variable datasets –in quality and quantity. This thesis addresses different topics of geotechnical site characterization from a probabilistic perspective, with emphasis on offshore investigation, on the Cone Penetration Test (CPTu) and on Bayesian methodologies.The first topic addresses soil layer delineation based on CPT(u) data. The starting point is the recognition that layer delineation is problem-oriented and has a strong subjective component. We propose a novel CPTu record analysis methodology which aims to: a) elicit the heuristics that intervene in layer delineation, facilitating communication and coherence in interpretation b) facilitate probabilistic characterization of the identified layers c) is simple and intuitive to use. The method is based on sequential distribution fitting in conventionally accepted classification spaces (Soil Behavior Type charts). The proposed technique is applied at different sites, illustrating how it can be related to borehole observations, how it compares with alternative methodologies and how it can be extended to create cross-site profiles. The second topic addresses strain-rate corrections of dynamic CPTu data. Dynamic CPTu impact on the seafloor and are very agile characterization tools. However, they require transformation to equivalent quasi-static results that can be conventionally interpret, La caracterización geotécnica de un emplazamiento incluye la definición de la disposición de las unidades de suelo y el establecimiento de sus propiedades de ingeniería relevantes. Es una actividad en la que siempre están presentes incertidumbres y en la que la cantidad y las caracteristicas de los datos disponibles son muy variables. Para evaluar y gestionar las incertidumbres se aplican metodologías probabilísticas. Una perspectiva bayesiana de la probabilidad es muy adecuada para la caracterización geotécnica, ya que tiene flexibilidad para manejar incertidumbres y datos muy variables. Esta tesis aborda diferentes temas de caracterización geotécnica desde una perspectiva probabilística, con énfasis en la investigación en alta mar, en el ensayo de penetración de cono (CPTu) y en las metodologías bayesianas El primer tema aborda la delineación de la capa de suelo basada en los datos CPT(u). El punto de partida es el reconocimiento de que la delineación de capas tiene un fuerte componente subjetivo. Proponemos una novedosa metodología de análisis de registros CPTu que tiene como objetivo: a) expresar la heurística que interviene en la delineación de capas, facilitando la comunicación en la su interpretación b) facilitar la caracterización probabilística de las capas identificadas c) uso sencillo e intuitivo. El método se basa en el ajuste de distribuciones secuenciales en espacios de clasificación (tablas de comportamiento del suelo). La técnica propuesta se aplica en diferentes emplazamientos, ilustrando cómo puede relacionarse con sondeos, cómo se compara con metodologías alternativas y cómo puede ampliarse para crear perfiles entre emplazamientos. El segundo tema aborda las correcciones de la velocidad de deformación de los datos del CPTu dinámico (que impactan en el fondo marino y son herramientas de caracterización muy ágiles). Sin embargo, requieren una transformación a resultados equivalentes que puedan ser interpretados convencionalmente. Hasta ahora las cor, Postprint (published version)

CPTu-based soil profiling has become a key component in the geotechnical design process. However, this is an interpretative process, affected by the inherent variability of soil properties, measurement noise and subjective heuristics. These are difficult to communicate to other interpreters or, even for the same interpreter, to transfer across profiles. A semi-automated tool for CPTu data interpretation is presented as an aid in this interpretation process. A probabilistic-based algorithm is employed to elicit the implicit heuristics in CPTu-based soil profiling and facilitate transference. Univariate normal distributions fit Soil Behavior Type Index data. Soil class boundaries, taken from a conventionally accepted chart, are sequentially activated with user-specified refinement. Thin layers under cone resolution are merged using well-established criteria. An application to CPTu records on finely interlayered deltaic deposits is illustrated, in which output delineations resulting from different analyst choices are compared among themselves and with one based on core description., Peer Reviewed, Postprint (published version)

Dynamic Cone Penetration Tests (CPTu) profile offshore sediments by impact penetration. To exploit their results in full the measured data is converted to obtain a quasi-static equivalent profile. Dynamic CPTu conversion requires calibrated correction models. Calibration is currently done by using paired (i.e., very close) quasi-static and dynamic tests. It is shown here that paired test data, which may be inconvenient to acquire offshore, are not strictly necessary to convert dynamic CPTu data. A new probabilistic methodology is proposed to call upon quasi-static results from a much wider area in the conversion procedure. Those results feed the prior distribution of a converted profile, within a Bayesian updating scheme where strain rate coefficient and correction model error are also described by updated stochastic variables. The updating scheme is solved numerically using the Transitional Markov Chain MonteCarlo sampling algorithm. To avoid undue influence of local profile heterogeneity, the statistic treatment of the quasi-static CPTu data takes place in the frequency domain, using a discrete cosine transform (DCT). The new procedure is applied to a CPTu campaign offshore Nice (France): dynamic tests are converted with equal precision using quasi-static data acquired at distances orders of magnitude larger than what was previously employed., Peer Reviewed, Postprint (author's final draft)

El margen continental Suroeste de la Península Ibérica es investigado a causa de su frecuente actividad tectónica, en la que se catalogan fenómenos de deslizamiento. Principales retos de la zona de estudio es el desarrollo de mapas de riesgo de deslizamientos submarinos, provocados por terremotos, relacionados a posible generación de tsunamis. El caso de estudio aumenta en tres órdenes de magnitud la extensión de los precedentes. El cálculo de la susceptibilidad presenta varios retos debido a limitados datos geotécnicos, el escaso conocimiento de las variables de control y las incertidumbres en los mecanismos de activación. Para hacer frente a estos problemas, este estudio propone una metodología probabilística basada en un modelo geotécnico, cuyo objetivo es reducir la gama de factores y que aborda la incertidumbre de los parámetros del modelo de una manera sistemática y racional para derivar un mapa probabilístico de susceptibilidad a los deslizamientos., Postprint (published version)

The Gulf of Lions presents recurring mass-transport deposits (MTDs) within the Plio-Quaternary sediments suggesting a long history of mass movements. The two large, surficial MTDs are located on the eastern and western levee of the Rhone canyon over an area exceeding 6000 km2 and volumes exceeding 100 km3. Both MTDs were emplaced 21 ka ago (peak of the Last Glacial Maximum), suggesting a common trigger. Here, we present a multidisciplinary high-resolution geophysical, sedimentological and in-situ geotechnical study of the source and deposit areas of both MTDs to characterise distinct expressions of sediment deformation as well as their spatial and chronological distributions. We show the internal structure of mass movements and resulting MTDs with unprecedented details that were previously represented in the conventional seismic data as transparent and chaotic facies. The combination of multidisciplinary approaches shows new insights into the nature of basal surfaces of the slope failures. In particular, we show that the basal surfaces of the failures consist of clay-rich material contrasting with the overlying turbiditic deposits, suggesting that a strong lithological heterogeneity exists within the strata. We suggest that this change in lithology between clay-rich sediments and turbiditic sequences most likely control the localisation of weak layers and landslide basal surfaces.

The SW Iberian continental margin is well recognized as a tectonically active area, where major canyons and mass wasting events are both present. Earthquake triggered submarine landslides may cause tsunami and result in catastrophic damage to bordering coastal areas. In this setting, submarine landslide susceptibility mapping represents a major step towards a regional risk mitigation strategy. Landslide susceptibility mapping in large offshore areas presents significant challenges as a result of the limited information on controlling variables, large uncertainties in triggering mechanisms and limited geotechnical data. In this study, a geotechnical model-based approach has been followed that narrows the range of controlling factors and, within a probabilistic framework, allows a systematic treatment of parameter uncertainties. This model-based analysis covers the whole SW Iberian margin increasing by three orders of magnitude the areal extent of precedent offshore slope stability susceptibility studies. This jump in spatial scale is facilitated by application of a systematic Bayesian updating procedure, to combine geotechnical information from global databases and that available from regional sites. Seismic shaking is estimated using an available regional database of seismogenic faults. These tools are implemented within a GIS to generate, via Montecarlo simulations, probabilistic landslide susceptibility maps based on two different analytical seismic infinite slope stability models. These models differ mainly in the form of their final results, either as distributions of slope stability safety factors or as distributions of seismic-triggered slope displacements. Receiving Operator Curves are used to assess the different landslide susceptibility predictions obtained against a comprehensive regional database of submarine landslides. It turns out that the models analyzed correctly predict 92% and 82% of the mapped landslide subset chosen for validation for pseudo-stat

The Gulf of Lions presents recurring mass-transport deposits (MTDs) within the Plio-Quaternary sediments, suggesting a long history of mass movements. The two large, surficial MTDs are located on the eastern and western levee of the Rhone canyon over an area exceeding 6000 km2 and volumes exceeding 100 km3. Both MTDs were emplaced 21 ka ago (peak of the Last Glacial Maximum), suggesting a common trigger. Here, we present a multidisciplinary high-resolution geophysical, sedimentological and in-situ geotechnical study of the source and deposit areas of both MTDs to characterize distinct expressions of sediment deformation as well as their spatial and chronological distributions. We show the internal structure of mass movements and resulting MTDs with unprecedented details that were previously represented in the conventional seismic data as transparent and chaotic facies. The combination of multidisciplinary approaches shows new insights into the nature of basal surfaces of the slope failures. In particular, we show that the basal surfaces of the failures consist of clay-rich material contrasting with the overlying turbiditic deposits, suggesting that a strong lithological heterogeneity exists within the strata. We suggest that this change in lithology between clay-rich sediments and turbiditic sequences most likely controls the localization of weak layers and landslide basal surfaces

The SW Iberian continental margin is well recognized as a tectonically active area, where major canyons and mass wasting events are both present. Earthquake triggered submarine landslides may cause tsunami and result in catastrophic damage to bordering coastal areas. In this setting, submarine landslide susceptibility mapping represents a major step towards a regional risk mitigation strategy. Landslide susceptibility mapping in large offshore areas presents significant challenges as a result of the limited information on controlling variables, large uncertainties in triggering mechanisms and limited geotechnical data. In this study, a geotechnical model-based approach has been followed that narrows the range of controlling factors and, within a probabilistic framework, allows a systematic treatment of parameter uncertainties. This model-based analysis covers the whole SW Iberian margin increasing by three orders of magnitude the areal extent of precedent offshore slope stability susceptibility studies. This jump in spatial scale is facilitated by application of a systematic Bayesian updating procedure, to combine geotechnical information from global databases and that available from regional sites. Seismic shaking is estimated using an available regional database of seismogenic faults. These tools are implemented within a GIS to generate, via Montecarlo simulations, probabilistic landslide susceptibility maps based on two different analytical seismic infinite slope stability models. These models differ mainly in the form of their final results, either as distributions of slope stability safety factors or as distributions of seismic-triggered slope displacements. Receiving Operator Curves are used to assess the different landslide susceptibility predictions obtained against a comprehensive regional database of submarine landslides. It turns out that the models analyzed correctly predict 92% and 82% of the mapped landslide subset chosen for validation for pseudo-stat, This research received funding from the European Union's Horizon 2020 research and innovating programme under the Marie Sklodowska-Curie grant agreement No 721403. The Spanish “Ministerio de Ciencia e Innovación” and the European Regional Development Fund through grant CTM2015-70155-R (project INSIGHT) are also acknowledged., Peer Reviewed, Postprint (published version)

Evaluation of geotechnical parameters on a project site is a necessary step in geotechnical engineering. However, due to the inherent variability of soil properties and the lack of data, many unavoidable uncertainties arise during a site-specific geotechnical characterization. This challenging task can be addressed under the Bayesian framework. The aim of this paper is to apply the Bayesian approach to a reference example of friction angle evaluation in sand, using the Bayesian Equivalent Sample Toolkit (BEST). BEST is an Excel VBA program for probabilistic characterization of geotechnical properties. In particular, in this study the statistical analysis has been performed using CPT tests from reference field studies. The results obtained for one case study involving CPT are discussed., The first author’s work has been supported by the European Innovating Training Network SLATE (H2020-MSCA-ITN-201)., Postprint (published version)