Keynote Lectures  

Mitchell Lecture

Fernando Schnaid

On the geo-mechanics and geo-characterization of tailings

The prediction of the short and long-term properties of silty and sandy tailings is among the greatest geotechnical and geoenvironmental challenges of our time. Governed by flow and cyclic liquefaction, the engineering characteristics of tailings under shear are dictated by the development of large strains, accompanied by increases in pore pressures and reduction in deviatory and mean stresses. This phenomenon can be described under the concepts of Critical State Soil Mechanics by modelling some specific aspects of behaviour such as the unstable strain-softening response and the shape of the critical state line. In situ tests can only be interpreted with reference to this framework. In addition, it is recognized that, as intermediate permeability materials, in situ test results can only be analysed after full account for the drainage effects taking place during shearing. All these aspects are reviewed in this paper and guidance for industry is provided on the theoretical background and techniques required to maintain mineral supplies while reducing catastrophic failures, loss of lives and environmental consequences of mining extraction. It is acknowledged that industry funding along with government support were critical to the development of the present work.

Kenneth H. Stokoe

The Increasing Role of Seismic Measurements in Geotechnical Engineering

Jason T. DeJong, Christopher P. Krage, Ross W. Boulanger, Don J. DeGroot

Optimization of CPT Soundings to Reduce Uncertainty in Interpretation of Subsurface Stratigraphy

The site characterization objectives for a project are typically focused on determining the types of soil present, the engineering properties of these soils, and the stratigraphic structure of the subsurface. Often, there is a greater emphasis and more systematic evaluation of the soil properties, while the subsurface stratigraphic units, including their boundaries, vertical and lateral continuity, etc., are assessed in a more ad-hoc manner with greater reliance on engineering judgement. The engineering judgement employed often assumes the subsurface to be more uniform that it actually is. This paper presents a framework using geostatistical methods to more quantitatively design and adapt site investigation programs to better estimate the subsurface geologic conditions while still evaluating soil types and engineering properties. This is exemplified first using an idealized synthetic 3D site and second through a 2D cross-section of a real project site. For the former, an idealized 3D site is used to evaluate the effect of sounding number and spatial distribution on calibration of a geostatistical model and the subsequent calibrated realization of subsurface conditions. Grid, nested, and combined grid-nested sampling patterns are used to calibrate and condition 3D transition probability geostatistical models of subsurface variability. The ability to identify spatial correlation from various number and patterns of exploration locations is presented and discussed. Analysis of a 2D cross-section at a real project site is then used to apply the observations made, delineating how assumptions in the geostatistical model and the number of CPT soundings can be used to refine a subsurface geologic model. This set of analyses lead to recommendation of a sounding spacing to correlation length ratio that is necessary to accurately quantify the spatial variability conditioned on discrete sampling locations.

Ray Wood

Unforeseen conditions represent a significant risk to the delivery of major civil engineering and building projects often leading to overruns in cost and time. This paper examines the importance of a managed approach to reduc-ing site characterization uncertainty and summarizes recent advances in the tools and techniques available to the geotech-nical engineering industry to optimally plan and execute site characterization programs to the benefit of the key project stakeholders, namely owners/developers, designers and constructors. Recent developments in remote sensing, geophysi-cal surveying, in-situ probing, continuous soil coring and geodata management are described.

Silvano Marchetti Lecture

D. M. Berisavljevic, Z. M. Berisavljevic

Dilatometer and seismic dilatometer tests in different depositional environments

Seismic dilatometer has been established as a common investigation tool for site characterization. Results obtained at two test sites using a seismic dilatometer, equipped to record both P- and S- waves (SPDMT), are presented in the paper. At Belgrade Waterfront test site soil is young, NC, “well-behaved” which makes DMT measurements (A, B) and DMT standard interpretation procedure accurate in predicting geotechnical parameters. At Kuzmin test site results of dilatometer test are more difficult to interpret since partial drainage conditions emerge during test performance. A procedure that compensate for errors that are introduced by the partial drainage conditions is applied to restore undrained A and B values from the dissipation curve. These undrained values are used in standard DMT interpretation procedure to yield geotechnical parameters. DMT parameters derived from consideration and without consideration of partial drainage effects are compared. Results of both P- and S- wave velocity measurements and interpretation are presented.

Invited Lectures  

Helmut Schweiger, Marcos Arroyo, Laurin Hauser

Recent Advances in Numerical Modelling of CPT

The numerical simulation of cone penetration tests (CPT) involves large deformations and large displace-ments leading to severe mesh distortion and therefore standard displacement based finite element formulations are not suitable for solving this type of problems. In this work the Particle Finite Element Method code G-PFEM, which employs an updated Lagrangian description, is utilized. The use of linear elements in combination with a stabilized mixed formu-lation and frequent remeshing of critical regions ensures computational efficiency. The well-known Clay and Sand Model (CASM), which is a model based on critical state soil mechanics principles, has been implemented in G-PFEM and extended to account for effects of bonding and destructuration. In this contribution two aspects are addressed, firstly the influence of bonding on cone resistance and the correlation with the undrained shear strength. Secondly the influence of the constitutive model on cone resistance and undrained shear strength by changing the shape of the yield surface of the Clay and Sand Model.

Joek Peuchen

Geo-intelligence from databases of offshore in-situ tests in public domain

In situ test data are increasingly available in public domain databases. Key drivers for Europe are the energy transition initiatives and the European INSPIRE directive for spatial information. What is available and how can we use such geodata now and for future geo-intelligence? Can we develop enhanced site-specific parameter values? Can we improve spatial parameter assessment by integrating in situ test data with ultra-high resolution seismic reflection data? Examples are presented for in situ test data available in the public domain for the Dutch sector of the North Sea, particularly for rapidly expanding wind energy assets. In-situ data sets mainly cover piezocone penetration tests (CPT), seismic CPTs and borehole geophysical logging results.

Rainer Massarsch, B. H. Fellenius, M. Terceros H. 

Compressibility of granular soils from CPTU and DMT

The compressibility of a granular soil is evaluated, based on CPTU and DMT data. A concept is described how the cone resistance can be adjusted with respect to the mean effective stress in order to reflect soil strength and stiffness independent of depth. This stress adjustment makes it possible to estimate the tangent modulus number and the constrained modulus, based on cone resistance measurement. The constrained modulus as measured by DMT was con-verted into tangent modulus number. Thus, it is possible to compare the tangent modulus number and constrained modulus obtained from CPT and DMT measurements, respectively. The results of extensive CPTU and DMT investigations from an ISSMGE test site, composed of sand and silty sand, were analyzed to determine the stress conditions and compressi-bility. Empirical values of the modulus number, published in the literature, are generally representative for normally consolidated soils. In the present study, a concept is presented how the effect of stress history (pre-loading) on the modulus number and the tangent modulus can be taken into account. The constrained modulus derived from CPTU and DMT results are compared and show good agreement.

Catherine Jacquard

The pressuremeter: recent developments in testing and design methods

This lecture concerns both the on-site implementation of tests and the qualification of new tools, as well as new calculation developments from measurements made with different types of standard or innovative pressuremeters. It takes up some developments of works carried out within the framework of the collaborative research project ARSCOP.

Don J. DeGroot, Jason T. DeJong, Oyvind Blaker, Willian G. Lukas, Christopher P. Krage

Recent advances in sampling and laboratory characterization of intermediate soils

Intermediate soils encompass an array of natural deposits, such as silts, silty clays, clayey silts, sandy silts, among others, and they usually exhibit transitional behavior with some properties being clay-like and others being sand-like. Despite intermediate soils being frequently encountered on infrastructure projects worldwide they remain challeng-ing to sample and characterize. This paper presents results from recent research on sampling and laboratory characteriza-tion of intermediate soils. An overview of the state of knowledge is presented and the challenges in sampling and labor-atory characterization of intermediate soils relative to the more well-established norms for clays and sands are highlighted. Results from sampling and advanced laboratory characterization tests using a suite of reconstituted synthetic soils and intact samples of the low plasticity index Halden silt are presented. Key findings from a synthesis of the research includes: 1) it is possible to collect intact downhole block samples of a low plasticity, low clay fraction silt, 2) poor tube geometry samplers create sample disturbance that results in markedly different undrained shear behavior compared to undisturbed sample behavior, 3) whereas good tube geometry fixed piston sampling can collect samples of similar quality to that of a block sample, 4) significantly disturbed samples show relatively little change in volume and largely recover any loss in shear wave velocity during laboratory reconsolidation to in-situ effective stresses, 5) a recently developed work-based sample quality criteria appears to track well the effects of sample disturbance independent of plasticity and stress history, 6) 1-D consolidation behavior of even good quality samples do not show any visual evidence of stress history, and 7) selection of undrained shear strength for design for intermediate soils that exhibit dilative behavior is complicated and requires careful assessment of the field loading regime and drainage conditions.

Jean-Sebastien L'Heureux, T. Lunne

The Norwegian GeoTest Site infrastructure

Benchmarking is a key to the reliability of solutions in geotechnical engineering. Throughout the world, a system of geotechnical experimentation sites with a wide range of geological ground conditions is available for testing and verifying innovative soil investigation methods and calibrating foundation solutions. These benchmark test sites provide easy access to well-characterized and documented field test sites for advancing the state of the art in areas such as in situ testing, instrumentation, prediction of soil behaviour, and foundation prototype testing. This lecture will give a short review of Norwegian experience with benckmark test sites and show examples of the practical use of geotest sites.

Sebastiano Foti

Uncertainties in seismic site characterization

Site characterization for seismic projects requires additional information on top of those which are required for any geotechnical design. Specifically, the investigation of the response of soil deposits to cyclic and dynamic actions has been recently included in the draft of the new generation of Eurocode 7 part 2 on ground properties. In this context geophysical tests play a role of paramount importance in site investigation. Moreover, seismic tests provide the oppor-tunity to estimate the small strain elastic moduli which can be useful for several geotechnical applications. Efforts are required to guarantee a sufficient quality of in situ and laboratory tests. However, benchmark tests have shown the exist-ence of a certain level of “uncompressible uncertainty”. Stochastic models can then be used to manage these uncertainties and evaluate their impact on modeling of site response and soil-structure interaction.

Patrick Mengé

Compaction Control of Offshore Land Reclamations by In Situ Tests

When performing land reclamation works by dredging and hydraulic fill placement, the contractual re-quirements and environmental situation will dictate the need for Ground Improvement. Land reclamations works in-volve extensive filling works where large volumes of fill must be placed. With such Ground Improvement, the need for quality assessment/quality control (QA/QC) becomes obvious. The paper discusses typical situations with land reclamation works where ‘suitable’ and ‘unsuitable’ materials are de-fined for the realization of land reclamations. Subsequently several requirements are given which lead to the need for monitoring and testing. Sometimes even very high numbers of tests and monitoring positions/types are required, leading to an intensive testing infrastructure to be set up, dedicated organization, testing database, leading to an important cost. The availability of ‘suitable’ material and its mineralogy may lead to compromises between ‘textbook’ materials and economically available materials. In such cases, testing and demonstration of the ‘functional’ behavior becomes even more important.

Serge Varaksin, Babak Hamidi

The contribution of CPT and PMT for optimization of a ground improvement project in Hungary

Excluding the staged surcharging period, the second section of the M7 Motorway along Lake Balatun in Hungary had to be constructed within a period of less than 2 years. The soil profile comprised very soft peaty soils that thickened in the southbound direction. As the embankment height also increased in the same direction, this would have resulted in severe stability issues and excessive settlement problems; hence, ground improvement was applied to allow the safe construction of the project within the specified performance criteria. In-situ tests using CPT and PMT were used to properly and appropriately select and execute suitable treatment methodologies over an area of approximately 400,000 m2. Dynamic replacement, the combination of dynamic and CMCs, the combination of dynamic replacement and surcharging, and vertical drains with surcharge were used within the various section to satisfy the project specifications.

António Viana Da Fonseca, C. Ferreira, J. Quintero, M. Millen

Equivalent Soil Profiles: CPTu-based soil classification for LIQUEFACT

CPTu testing is an extremely valuable tool for site characterization, with multiple applications in geotech-nical design and practice, namely for soil profiling and characterization, foundation design, liquefaction susceptibility and ground improvement control. In this work, a new application of CPTu data is presented, consisting of the definition of Equivalent Soil Profiles (ESP) for soil profiling and classification, to be implemented in numerical models, particularly for soil-foundation-structure interaction studies in shallow-founded buildings in liquefiable soils. While this classification is based on the estimate of cyclic resistance of the soil, it is hazard-independent, consisting on the definition of an equiv-alent 3-layered soil profile. The classification is based on only three features, highly influential to the performance of buildings: the depth of the non-liquefiable crust, the liquefaction resistance of the potentially liquefiable soil layer and its thickness. The selection of these parameters is justified by its influence on the ground surface acceleration and on the bearing capacity of shallow foundations. One of the most relevant advantages of this classification is the consideration of the performance of buildings in the event of liquefaction. A case study in the greater Lisbon area has been studied, where the procedures and classification of this innovative methodology are discussed. Finally, the comparison of LSN results of the original and the equivalent soil profiles is presented.

Richard Jardine

Recent developments in CPT based design procedures for driven piles

Richard P. Ray, Akos Wolf, Orsolya Kegyes-Brassai

Harmonizing Dynamic Property Measurements of Hungarian Soils

With the adoption of EC-8, geotechnical engineers in Hungary found themselves on unfamiliar ground. Previous codes required little in the way of dynamic properties (vs, Gmax, Gred, D) and seismic assessments were performed for critical sites only (nuclear power). The new code required new assessment methodologies, new measurements, new analyses, and new cooperation with structural engineers and architects. This presentation will illustrate some of the challenges in harmonizing various field and laboratory tests, as well as their use in design and analysis. Studies at Széchenyi University, as well as work with geotechnical consultants, attempted to maximize the usefulness of field, laboratory and performance data to generate a holistic, consistent set of dynamic properties of several categories of Hungarian soils. The effort has resulted in a robust, reliable set of properties and correlations which will serve as a basis for future research, design and construction.

Cor Zwanenburg, Bo Vesterberg, Priscilla Paniagua, Mike Long

ELGIP peat group – outline of research into peat behaviour

This paper summarises some of the work to date of the ELGIP working group on peat. ELGIP stands for European Large Geotechnical Institutes Platforms and has a dedicated group working on peat behaviour. The main pur-pose of the group is to collaborate in solving engineering peat related problems and improving tools for practical engi-neering. The group is working towards a common understanding of the peat mechanics, geology, geophysics and chem-istry, by experimental laboratory and field tests and numerical simulations. The paper will outline some of the progress that has been made by group members in recent years for example:

• the full-scale field trials, the large diameter sampler, the large triaxial and direct simple shear tests conducted by Deltares,
• the novel 1g laboratory model tests carried out by SGI to aid
• the understanding of embankment foundations in peat
• the characterisation of peat in the Trondheim area of Norway by NGI,
• the use of geophysical techniques for the purposes of peat characterisation by UCD.

Klaus Thoeni - Stephen Fityus - James Cudmore - Anna Giacomini

Structural characetrisation of rock mass defects: a comparison of traditional and emerging technologies

Emerging technologies are revolutionising the way in which rock mass defects are being characterised. The traditional approach of measuring rock discontinuities using a geological compass is being replaced, both by alter-native direct-contact measurement devices as smartphones with applications that directly give dip and dip direction, and by low-cost non-contact approaches such as photogrammetry performed on digital images to develop a 3D model of the rock face, thereby allowing virtual measurements of discontinuities to be taken. This paper presents a comparison of the accuracy of these different approaches to gathering orientation data (dip angle and dip direction) for discontinuities in natural rock masses, with accompanying consideration of the efficiency and relative cost of various contact and non-contact methods. Two mobile phones with different apps were used to take contact measurements and several different cost/quality image sensors were used to capture digital images for the photogrammetric models. Several image sets were collected and subsequently processed using Agisoft Metashape to develop 3D point clouds and eventually a high-resolu-tion 3D model. The open-source package CloudCompare was used to virtually take measurements of the features. The average of conventional geological compass measurements was used as a benchmark. From the results, most of the meth-ods were generally found to be acceptably reliable. Of the results from the smartphone applications, that of the iPhone 4 (an older generation) was more unreliable. It provided inaccurate dip direction due to the device constantly requiring calibration. Generally, the dip angle was approximated better than the dip direction for both devices. The photogrammetric models provided results closest to the compass from the highest quality sensor as expected. All models performed rela-tively well, the dip angle was close to the compass for most approaches, and the dip direction provided least error on the higher accuracy approaches.

Paul Mayne

Validation of the GT direct CPT footing method

A Georgia Tech direct CPT method for vertically-loaded shallow foundations provides the magnitudes of displacements and bearing capacity using a simple algorithm that was developed from analyzing full-scale load test data on 70 footings situated on sands, silts, clays, and fissured geomaterials. Since publication in 2014, new footing load test data have become available that provide an opportunity to independently cross-check the method. Four new case studies involve footings on: natural sand, dynamically compacted sand, natural soft clay, and partially saturated silt. In addition, measured settlement data compiled from 5 prior databases totaling some 60 very large footings from buildings and bridges on granular soils also confirm the general trends at working load design.

Marcos Arroyo

Geotechnical characterization: does it fit in a code? An European perspective

Imre Emőke

Evaluation of total stress dissipation test data

At present only approximate methods are available for the evaluation of the totals tress dissipation test since the models do not predict any total stress decrease. The paper makes an analysis of the existing models and a new model is suggested. The total stress dissipation test is suggested to be evaluated by the new, so called coupled 1 models with a time dependent constitutive law, eg., by adding a relaxation part-model.

In detail, two linear, point-symmetric, coupled consolidation model families with various embedding space dimension values (oedometer models: 1, spherical models:3, cylindrical models:2), differing in one boundary condition (coupled 1: constant displacement, coupled 2: constant stress) are analysed analytically and numerically. The method of the research is partly analytical, the models are unified into a single model with unique analytical solution, every model can be derived
from this by inserting the proper boundary condition and embedding space dimension _m_. The constants of the solutions are determined and an approximate time factor and model law are derived for the _m_ >1 case which is identical to the one valid in the oedometer (_m_ =1) case. The convergence of the infinite series are examined in the function of the initial condition. Concerning the total stress at the pile shaft, significant decrease (with the value of the initial mean pore water pressure) is encountered for the coupled 1 consolidation models, zero stress drop is resulted by the coupled 2 models. The rate of convergence of the Bessel series is the smaller if the initial condition is the closer to the one of a zero solutions. Beyond the trivial one, a non-trivial zero solution exists for the coupled 1 model, at the Terzaghi‘s initial condition.

L. Völgyesi, Gy. Tóth, Cs. Égető, B. Kiss, E. Fenyvesi, G. G. Barnaföldi, P. Lévai, Gy. Szondy, P. Ván

Current use of Eötvös Torsion Balance, the tidal effect

In the 20th century, many torsion balance measurements had been carried out around the world. The measurements still provide a good opportunity to detect the lateral underground mass inhomogeneities and the geological fault structures using the so called edge effects in gravity gradients. Usually, the horizontal gradients were used for geophysical prospecting, but the curvature gradients measured by torsion balance remained unused. However, curvature gradients are instrumental data in geodesy, using these gradients, precise deflections of the vertical can be calculated by interpolation and the fine structure of the potential surfaces of the Earth can be derived. Based on the horizontal and the curvature gradients of gravity, the full Eötvös tensor (including the vertical gradients) can be derived by the 3D inversion method. Application of torsion balance is also important in physics. Lorand Eötvös and his colleagues Dezső Pekár and Jenő Fekete executed a series of measurements (EPF experiment) from 1906 till 1908 to validate the equivalence of gravitational and inertial mass. Repeating this experiment by using a 90 years old, high precision torsion balance, but under better conditions with and applying the current modern technology for enhancing the precision, exposing and filtering out tiny environmental disturbances and barely perceptible flaws in instruments is a big challenge today.

Rainier Arndt, Walter Frei, Dieter Martin

P- and S-Wave Hybridseismics: Non-Destructive Geotechnical Site Characterizations Using State-Of-Science Surface Geophysics

Geophysical ground investigations are not a substitute for boring and direct physical testing. Rather it complements a well-planned, cost-effective drilling, sampling and testing program. Geophysics, among the methods hy-brid seismic, provide a continuous image of the subsurface rather than CPT point measurements. No one cares about geophysics unless it solves geological / geotechnical problems and saves resources: High resolution seismics is a legacy problem solver for the civil engineer community. Since 2000 hybridseismics - a simultaneously conduct of refraction- and reflection seismics followed by an intermeshed data processing scheme – represents the royal league of geophysical methods supporting site investigations. Hereby the underground is dual scanned by seismic waves revealing horizontal and vertical strata structures and rock velocity distributions hinting geotechnical unforeseen features in the underground. Hybridseismics works equally well with both body wave motions (compressional- and shear waves). Quality of results are achieved if field acquisition parameter harmonize with adequate near surface tuned data processing sequences (recip-rocal velocity calibration, congruency between event location and anomaly shape). Consequently, subjective initial as-sumptions of geological start models inherent for seismic standard inversion modelling is omitted. By applying both wave types in one survey, spatial in-situ distributions of YOUNG-modulus and POISSON ratios reveal from hybrid seismic cam-paigns.