Documents published in Scipedia

• PLENARY LECTURE - Simulation-aided geotechnical site investigation

  L. Monforte*, M. Arroyo, A. Gens

  ISC2024.

  
  

  Abstract

  With the advancement of computational geomechanics over the past decades, most of the activities typical of site characterization, such as in situ testing or sampling, can be realistically simulated using appropriate constitutive models and balance equations for geomaterials. These numerical simulations are not only informative of the processes that take place during testing but can be used to assess the reliability of current practice empirical interpretation techniques or even propose new interpretation techniques. In this paper, we present two numerical analyses of long-standing geotechnical problems in which new insights are gained by means of advanced numerical modelling. The first analysis corresponds to cone penetration testing in undrained, brittle geomaterials; we describe the effect of the constitutive parameters on cone metrics, and we propose a novel procedure to estimate the initial state parameter from CPTu based on a wide-ranging parametric analysis. The second analysis involves tube sampling in undrained geomaterials. A total stress analysis allows us to describe the kinematics of the soil during tube insertion and evaluate the effect of the tube geometry on the strain path of the problem. The analysis is then extended by considering a fully coupled hydromechanical formulation and a critical state constitutive model for cemented soils; by simulating conventional laboratory tests on the soil that has entered the tube we can quantify sampling disturbance in terms of geotechnical design parameters (e.g. undrained shear strength and yield stress). The possibilities offered by numerical modelling for site characterization are far from being fully exploited. It is envisaged that in the future site-specific numerical analyses will become available, enabling a more comprehensive understanding of the subsurface conditions.

  Abstract
  With the advancement of computational geomechanics over the past decades, most of the activities typical of site characterization, such as in situ testing or sampling, can [...]

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• PLENARY LECTURE - Treatment of uncertainties in site characterization in second-generation eurocode 7

  J. Estaire, T. Schweckendiek

  ISC2024.

  
  

  Abstract

  The purpose of this paper is to introduce the geotechnical engineering community to the treatment of uncertainties in site characterization within the framework of the second-generation Eurocodes. To do so, the main uncertainties related to the Ground Model, the ground properties and the groundwater levels are described before discussion of the statistical and modelling involved. This paper also explains the determination of “representative values” of ground properties within the framework of the Second-Generation Eurocode 7, either selecting the value based on engineering judgment and comparable experience, being in this case termed a “nominal value”; or evaluating the value by statistical methods, being in this case termed a “characteristic value”. Additionally, since 2nd-Gen Eurocode 7 allows using reliability-based methods for the verification of limit states, the paper gives some guidance for choosing probability distribution types, and for assessment their parameters like the mean and standard deviation. Finally, two examples are provided to show how to deal with the new elements involved with uncertainty treatment in terms of statistical analysis and probabilistic modelling

  Abstract
  The purpose of this paper is to introduce the geotechnical engineering community to the treatment of uncertainties in site characterization within the framework of the second-generation [...]

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• PLENARY LECTURE - Recent advancements in data-driven site characterization

  J. Ching*, K. Phoon

  ISC2024.

  
  

  Abstract

  This paper reviews some recent advancements that address the challenges faced by the broad application area of datadriven site characterization (DDSC). The challenges include the ugly-data challenge, site-recognition challenge, and stratification challenge. The ugly-data challenge is about the MUSIC-3X attributes of the site investigation data, where MUSIC-3X stands for multivariate, uncertain and unique, sparse, incomplete, possibly corrupted, and 3D spatial variability (3X). The site-recognition challenge is about the site-uniqueness feature of the site investigation data. The stratification challenge is about the task of layer delineation in soil profiling. In recent years, some studies have been conducted to address these challenges with an encouraging degree of success, which are briefly reviewed in this paper. However, there are still unresolved issues yet to be addressed, which are briefly summarized in this paper as well.

  Abstract
  This paper reviews some recent advancements that address the challenges faced by the broad application area of datadriven site characterization (DDSC). The challenges include [...]

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• PLENARY LECTURE - Combined resistivity and seismic measurements along linearly extended earth structures - acquisition and interpretation approaches

  C. Comina*

  ISC2024.

  
  

  Abstract

  Geotechnical parameters of linearly extended earth structures, such as embankments and earth dams, are usually obtained from localized investigations through drilling or penetration tests, commonly time and cost consuming. Non-invasive geophysical investigations may be considered an alternative approach for the geotechnical characterization of these structures, given their surveying speed and their depth and length of investigation. Particularly, new acquisition approaches with the use of appropriate streamer cables could strongly reduce the acquisition times making geophysical surveys ideal for a preliminary screening of these structures. Specifically, resistivity and seismic methods can be adopted given that these two methodologies could offer complementary information with respect to the pore fluid properties (resistivity methods) and the solid skeleton characteristics (seismic methods). Also, through specific correlations, relevant geotechnical parameters for the evaluation of the stability of these structure and its efficiency (i.e. hydraulic conductivity, porosity and others) can be obtained. In this paper a review of the methodologies developed in recent years for data acquisition along linearly extended earth structures is reported with special focus on the use of combined electric and seismic streamer cables. Suggestions with respect to interpretation approaches and data elaboration are also analysed.

  Abstract
  Geotechnical parameters of linearly extended earth structures, such as embankments and earth dams, are usually obtained from localized investigations through drilling or penetration [...]

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• PLENARY LECTURE - Passive seismic methods for site characterization

  C. Cornou*

  ISC2024.

  
  

  Abstract

  Site characterization methods to extract the shear-wave velocity (Vs) structure over the first few tens to few hundred of meters or the soil’s resonance frequency using seismic noise recordings have become widespread over the last 40 years. Being cost-effective and easy to implement, especially in urban environment, passive seismic methods have been shown reliable to retrieve the soil resonance frequency and the Vs profile of near-surface geological layers. International efforts over the last 20 years have outlined the capabilities and limitations of passive seismic methods and lead to a series of good-of-practice, state-of-the-art and recommendations on data acquisition and processing. Recent methodological developments using three-component single-station and three-component array methods are promising approaches to better constrain Vs profiles. Also, the very high spatial and temporal resolution offered by the Distributed Acoustic Sensing (DAS) makes this emerging technology one with very high potential for near-surface site characterization, especially in urban environment.

  Abstract
  Site characterization methods to extract the shear-wave velocity (Vs) structure over the first few tens to few hundred of meters or the soil’s resonance frequency using [...]

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• PLENARY LECTURE - Machine learning tools for the treatment of offshore site investigations

  B. Stuyts*

  ISC2024.

  
  

  Abstract

  During geotechnical and geophysical site characterisation for large infrastructure projects, significant data volumes are being collected which need to be processed and interpreted. Due to the limited budgets available for site characterisation and the various sources of uncertainty, the interpretation relies on a combination of data from various sources (e.g. in-situ and laboratory tests), the use of parameter correlations from the literature and expert judgement. In recent years, modern data science techniques have become increasingly accessible to practicing engineers and researchers and they offer the possibility to improve several aspects of the site characterisation and parameter selection process. Machine learning models can be trained on high-quality datasets and expert judgement can also be internalised in the model formulations. In this contribution, the role of data science and machine learning for geotechnical site characterisation is discussed based on several example applications using datasets from offshore wind farm projects. The role of data coverage and data quality is discussed as well as the role of geophysical data for interpolating geotechnical point measurements in a quantitative way. Supervised and unsupervised machine learning techniques are explained and illustrated on the provided datasets. Finally, a perspective is given on the role of the emerging Large Language Models (LLM) for geotechnical site characterisation applications.

  Abstract
  During geotechnical and geophysical site characterisation for large infrastructure projects, significant data volumes are being collected which need to be processed and interpreted. [...]

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• PLENARY LECTURE - Bio-inspired site characterization - towards soundings with lightweight equipment

  A. Martinez, Y. Chen, R. Anilkumar

  ISC2024.

  
  

  Abstract

  Equipment used for site investigation activities like drill rigs are typically large and heavy to provide sufficient reaction mass to overcome the soil’s penetration resistance. The need for large and heavy equipment creates challenges for performing site investigations at sites with limited accessibility, such as urban centres, vegetated areas, locations with height restrictions and surficial soft soils, and steep slopes. Also, mobilization of large equipment to the project site is responsible for a significant portion of the carbon footprint of site investigations. Successful development of selfburrowing technology can have enormous implications for geotechnical site investigation, ranging from performance of in-situ tests to installation of instrumentation without the need of heavy equipment. During the last decade there has been an acceleration of research in the field of bio-inspired geotechnics, whose premise is that certain animals and plants have developed efficient strategies to interact with geomaterials in ways that are analogous to those in geotechnical engineering. This paper provides a synthesis of advances in bio-inspired site investigation related to the (i) reduction of penetration resistance by means of modifying the tip shape, expanding a shaft section near the probe tip, applying motions to the tip like rotation and oscillation, and injecting fluids and (ii) generation of reaction forces with temporary anchors that enable self-burrowing. Examples of prototypes that have been tested experimentally are highlighted. However, there are important research gaps associated with testing in a broader range of conditions, interpretation of results, and development of hardware that need to be addressed to develop field-ready equipment that can provide useful data for geotechnical design.

  Abstract
  Equipment used for site investigation activities like drill rigs are typically large and heavy to provide sufficient reaction mass to overcome the soil’s penetration resistance. [...]

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• Impact of evolving fabric anisotropy on CPT simulations for subsurface characterization

  S. Moshfeghi, M. Taiebat*, A. Lizcano

  ISC2024.

  
  

  Abstract

  In geotechnical site characterization, Cone Penetration Testing (CPT) is a fundamental method for evaluating subsurface conditions of granular materials such as sands, silts, and non-plastic tailings. This study advances CPT simulations by incorporating the fabric anisotropy variable A into the SANISAND-F model and utilizing the Material Point Method (MPM), with a specific focus on the role of evolving fabric within an anisotropic critical state framework. The objective is to deepen the understanding of how the evolving fabric of soils influences macroscopic site characterization outcomes. Through carefully controlled initial conditions, including void ratio and confining pressure, the study aims to demonstrate the impact of fabric anisotropy on CPT resistance measurements. Assessment of the evolution of material state based on the key constitutive ingredient of the model allows for explaining the reason behind the respective values of cone tip resistance observed from the CPT simulations, considering fabric anisotropy and the anisotropic critical state framework. This approach enhances the modeling of this site characterization method, providing a more comprehensive framework for interpreting soil mechanical behavior and enhancing predictive modeling capabilities

  Abstract
  In geotechnical site characterization, Cone Penetration Testing (CPT) is a fundamental method for evaluating subsurface conditions of granular materials such as sands, silts, [...]

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• Use of the Pocket G-PFEM to Predict Changes in Soil State

  J. Carneiro*, M. Junior, A. Faria, G. Pinto

  ISC2024.

  
  

  Abstract

  Simulating the CPTu response to changes in the current soil state allows geotechnical engineers to evaluate different scenarios and better predict the structure’s performance. Developed by the Universitat Politècnica de Catalunya, Centre Internacional de Mètodes Numèrics en Enginyeria and TU Graz, the Pocket G-PFEM is a numerical tool that simulates the CPTu in a homogeneous soil layer, adopting an updated Lagrangian description. Two types of cones can be simulated: i) the smooth cone, without lateral friction in the interface cone/soil, and ii) the rough cone, with lateral friction. The Clay and Sand Model is adopted as the soil constitutive model. This study assessed the software response to changes in the overconsolidation ratio (OCR) and compressibility parameters (λ and κ) in both cone modules. The rough cone analyses resulted in higher qt and u1 than the smooth cone, but no significant change was observed in u2 and u3. The Pocket GPFEM could partially reproduce the expected behaviours from the literature, but u2 and u3 did not decrease significantly for high OCRs, and the rough cone could not adequately simulate the fs. Following the literature, qt was mainly sensitive to λ for the OCR = 1 and to κ for the OCR = 2, but an unexpected behaviour was observed for the OCR = 8 when changing λ and κ. The results show Pocket G-PFEM’s limitation in reproducing qt, fs, and u for high OCRs. It might be related to the adopted parameters, and different sets should be evaluated.

  Abstract
  Simulating the CPTu response to changes in the current soil state allows geotechnical engineers to evaluate different scenarios and better predict the structure’s performance. [...]

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• Types of Shearing and Anisotropy in Undrained CPTu

  D. Durán*, L. Monforte, M. Arroyo, A. Gens

  ISC2024.

  
  

  Abstract

  Most natural clays acquire an anisotropic fabric upon deposition. This anisotropic fabric induces differences in the soil mechanical responses, for instance in the undrained shear strength observed in the laboratory. It is unclear how much of that anisotropy is reflected on the responses measured by the cone penetration test. In this work, we use GPFEM to numerically simulate cone penetration tests (CPTu) in undrained, anisotropic clays. The constitutive response is represented by S-CLAY1, a critical state, anisotropic model. Full details of the representative stress path during CPTu insertion are provided. Preliminary numerical results suggest that even a large amount of anisotropy, as described by the model, will have a very small effect on the cone responses. The numerical simulation results also show that the prevailing stress path has strong similitudes with that found during anisotropically-consolidated undrained compression triaxial test.

  Abstract
  Most natural clays acquire an anisotropic fabric upon deposition. This anisotropic fabric induces differences in the soil mechanical responses, for instance in the undrained [...]

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