Colloquiam: 7th International Conference on Geotechnical and Geophysical Site Characterization (ISC7-24)

PLENARY LECTURE - The Legacy of Michele Jamiolkowski to Geotechnical Engineering

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:05:46 +0200

Michele Jamiolkowski was deeply interested in many topics in geotechnical engineering. The link between his many contributions to the discipline was his deep appreciation for the need to develop techniques for predicting the performance of real structures. This focus on real structures was pervasive in all of his research, and led to his attention to experimental investigation of natural soils. Jamiolkowski recognized the importance of in situ tests to site characterization of natural soils, and consequently this paper focuses on this topic. Jamiolkowski was involved in many challenging projects, and he always considered each project as an occasion to improve the state of the art, to develop novel approaches in site characterization, to develop new in situ test interpretation methods, and to obtain quality experimental data. The paper summarizes major improvements to the state of the art that resulted from his contributions, as well lessons learned from major and iconic projects in which Jamiolkowski was involved.

PLENARY LECTURE - Instrumental Dynamic Penetrometers for Geotechnical Characterization

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:05:30 +0200

The dynamic penetrometer is a common technique in geotechnical exploration and widely deployed throughout the world. However, while this technique has many advantages, it also has several disadvantages that can hinder its use and development. Indeed, it has evolved little, and its application has sometimes remained "rustic". But in recent years with the development of sensors, interpretation methods and digital technology, this technique has been adapted to improve the quality of measurement, the understanding of the phenomena occurring during the test and its exploitation. This article presents the recent developments and adaptations of this technique and their potential. After a brief review of the principle, history, and current limitations of the technique, we look at recent technological developments and the latest advances in terms of interpreting and using the test.

PLENARY LECTURE - Simulation-aided geotechnical site investigation

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:05:12 +0200

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.

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

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:04:57 +0200

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

PLENARY LECTURE - Recent advancements in data-driven site characterization

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:04:24 +0200

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.

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

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:04:10 +0200

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.

PLENARY LECTURE - Passive seismic methods for site characterization

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:03:57 +0200

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.

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

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:03:44 +0200

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.

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

Jesús Sánchez Pinedo — Mon, 10 Jun 2024 12:03:28 +0200

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.