Particle size distribution (PSD) is recognised among geotechnical engineers as an informative soil descriptor, and often used
to predict geomechanical behaviours. However, the effectiveness of PSD to characterise frost action is debatable. Existing criteria for assessing
frost susceptibility have relied on traditional PSD descriptors, such as Cu, which depend on individual parameters (i.e., d10, d60) which
explicitly neglect the effect of fines and gravel content. In turn, it has been reported that fines content is critical in the formation of
ice lenses. Grading entropy is a method which accounts for all the information in the PSD. In this work, normalised entropy coordinates are
used to review PSD-based frost susceptibility criteria and assess whether alternative PSD descriptors can more successfully characterise frost
action susceptibility. The effect of PSD (via grading entropy coordinates) on the development of frost heave is investigated using existing
experimental datasets. The findings in this work highlight significant variability in the PSD criteria, suggesting that PSD alone is not a
reliable indicator. However, examining experimental datasets indicated a clear effect of PSD using grading entropy coordinates for
understanding the development of frost heave.

Exploring the Use of Rock Flour for Sustainable Peat Stabilisation

Juan Bernal-Sanchez, Jamie Coll, James Leak, and
1 more author

This paper aims to investigate the mechanical behaviour of peat stabilised with glacial rock flour for foundation construction. Peat,
a natural organic soil, presents challenges for construction due to its high compressibility and low bearing capacity. This is an especially acute
problem in Scotland (UK) where 25% of the territory is covered by peat. Glacial rock flour, a fine-grained powder produced by the crushing of stone
in the construction industry, has been identified as a potential stabiliser for peat. This study evaluates the effect of varying percentages of
glacial rock flour on the mechanical properties of peat, considering the unconfined compression strength (UCS). The findings indicate a significant
improvement in UCS28 of the mixture with the addition of up to 15% rock flour. Hence, it is concluded that peat stabilisation with glacial rock flour
can be an alternative, cost-effective, and sustainable solution to the typically used excavate-and-replace technique in peatlands in the UK.

2023

Minimum dry density in terms of grading entropy coordinates

E. Imre, Daniel Barreto, M. Datcheva, and
4 more authors

In Smart Geotechnics for Smart Societies, Aug 2023

In this paper, the grading entropy method is applied together with advanced interpolation methods in order to establish empirical relationships
between grading entropy coordinates and minimum dry density of sands. Three databases consisting of 94 samples (in total) of artificial mixtures of
natural sands with fractal or continuous grain size distributions were used to evaluate three different types of empirical relationship. Whilst some
databases have been previously published, recently acquired data has also been considered. The results show that there is a strong relationship between
grading entropy coordinates and the minimum dry density.

A DEM study on the effect of inherent variability of assemblies of spherical particles

James Leak, and Daniel Barreto

In 10th European Conference on Numerical Methods in Geotechnical Engineering, Jun 2023

: This study presents DEM simulations of assemblies of spheres using periodic boundaries to assess the effect of
inherent sample variability. DEM specimens with different particle size distributions (PSDs) were randomly generated, and then
isotropically compressed prior to undrained (constant volume) triaxial shearing. DEM specimens with variable numbers of
spheres between 500 and 10000 were generated for each PSD. Sets of simulations therefore differed only in terms of the initial,
random positions of individual particles. Both macro- and micro-scale variables are then considered to assess the effect of
inherent variability on the numerical results. Results indicate that all variables are significantly affected by inherent variability,
however the range of variation generally decreased with an increase in specimen size. These results are some of the very first to
consider the effects of sample variability that may also be intrinsically present in physical laboratory experiments on granular
materials. They also highlight the importance of selecting DEM specimens of adequate size whilst considering the potential
(random) variability of their mechanical behaviour.

Use of hydraulic radius to estimate the permeability of coarse-grained materials using a new geodatabase

Shuyin Feng, Daniel Barreto, Emőke Imre, and
2 more authors

This paper reviews commonly used parameters and prediction models for assessing the permeability of granular soils. Following
a review of published models for prediction of soil permeability, a dimensional homogenous transformation model for a-priori estimation
of soil permeability was calibrated using a large database (CG/KSAT/7/1278) comprising permeability data for a wide range of granular
soils sourced from over 50 publications. The new transformation model requires knowledge of the void ratio and gradation of the material
to make estimates of the soil permeability. The prediction accuracy of the calibrated model was then assessed alongside that of other
empirical and semi-empirical models also calibrated using CG/KSAT/7/1278. The potential influences of void ratio, key gradation parameters
and permeability test type on the prediction accuracy of the proposed model are also examined. The paper shows that while the fitted
constants in the proposed transformation model are affected to varying extents by the aforementioned parameters, it does offer reasonable
predictions of permeability with only knowledge of the void ratio and material gradation required.

Soil parameters in terms of entropy coordinates

Emőke Imre, Tibor Firgi, Wiebke Baille, and
4 more authors

In 8th International Conference on Unsaturated Soils (UNSAT 2023), Apr 2023

In the ongoing research, an approximate, grading entropy based, advanced interpolation method is applied to establish empirical
functions between the grading curves and the model parameters of sands. The space of the grain size distribution curves with N fractions
is isomorphic to the space of the unit-sided simplex with dimension N-1. The traditional interpolation over the simplex with dimension N-1
is problematic since the number of the sub-simplexes (and the interpolation points) may increase exponentially with N. To overcome this
difficulty, the function is approximately interpolated, which means that the interpolation is made on some 2-dimensional sections of the simplex and is extended to the whole simplex, using the grading entropy map. Two kinds of 2-dimensional sections can be used based on either fractal distributions or partly fractal partly on some maximal gap-graded distributions. In this paper the experiments were made on the artificial mixtures of natural sand grains earlier. Two kinds of functions were approximately interpolated for the minimum dry density using the measured data. One kind of function was determined for the parameters of an SWCC model directly from the level lines previously graphically interpolated from fractal distribution data.

Rubber-soil mixtures: use of grading entropy theory to evaluate stiffness and liquefaction susceptibility

Juan Bernal-Sanchez, James Leak, and Daniel Barreto

Rubber-soil mixtures are known to have mechanical properties that enable their use in backfills, road construction
or geotechnical seismic isolation systems. The complexity of these mixtures comes from adding soft (i.e. rubber) particles that
increases the number of particle properties to consider when studying the macroscopic behaviour. The distinction between sand-like
and rubber-like behaviour is normally presented in relation to the rubber content and size ratio between particles. It is however
unknown how the change on the mixture gradation affects the mechanical behaviour of RSm. Entropy coordinates condense the entire
particle size distribution (PSD) to a single point on a Cartesian plane, accounting for all the information in the gradation. Grading
entropy coordinates have been used to study typical geotechnical behaviours of mostly incompressible (i.e. sand) soils. In this study,
entropy coordinates are used to analyse the correlation between the small-strain stiffness and liquefaction susceptibility of RSm and
their PSDs. The results suggest that entropy coordinates can be used effectively on RSm as an alternative means of assessment of
typical soil behaviours, being also able to distinguish between sand-like and rubber-like behaviours. Based on the 30 PSDs analysed,
it is also evidenced that internal stability criterion proposed by Lőrincz (1986) can be used to predict the liquefaction
susceptibility of RSm. The normalised base entropy (A) has also been shown to increase with the rubber content, which is linked to
a lower liquefaction susceptibility, due to the supporting effect of rubber particles on strong-force chains formed of sand particles.

Revisiting Hardin’s parameters for the quantification of particle breakage – A statistical entropy approach

James Leak, Daniel Barreto, Vasiliki Dimitriadi, and
1 more author

In Powders & Grains 2021 – 9th International Conference on Micromechanics on Granular Media, Aug 2023

It is well recognised that particle breakage in granular materials is affected by stress level, stress path, initial density, and particle
size distribution (PSD), amongst others. Furthermore, it has been shown that breakage has a significant influence on the stress-strain behaviour of
soils. This paper compares a commonly used breakage parameter with grading entropy coordinates. Such coordinates enable for the representation of any
PSD as a single point in a Cartesian coordinate plane. Hence, the evolution of PSD changes may be easily tracked. This paper aims to demonstrate that
grading entropy coordinates are as (or more) effective than other breakage parameters, whilst providing additional insight. On the basis of limited
data it is shown that grading entropy coordinates are able to capture the dependence of breakage on stress level, stress path and initial PSD.

2022

Quantifying Particle Breakage and Its Evolution Using Breakage Indices and Grading Entropy Coordinates

James Leak, Daniel Barreto, Vasiliki Dimitriadi, and
1 more author

Particle breakage in soils is a well-recognised behaviour. Conventional methods for quantifying the breakage process rely
on calculating the area between the particle size distribution (PSD) curves produced before and after crushing. A key aspect of
breakage is understanding the process across the different size/sieve fractions. Grading entropy coordinates allow for the
representation of any PSD to be shown as a single point on a Cartesian plane and are able to track grading evolution with relative
ease. In this study, grading entropy coordinates are compared to three commonly used breakage indices (Br, Br* and IG). It is shown
that grading entropy coordinates are advantageous over the traditional indices in quantifying subtle changes in the PSD evolution
and directly provide further insight with regards to the individual fraction sizes. It is also discussed that conventional breakage
indices rely on relative measures and are dependent on assumptions of an initial and/or final PSD. In contrast, grading entropy
coordinates depend only on the characteristics of the (current) PSD curve. It was also observed that the breakage evolution captured
by the entropy coordinates is able to determine the rate at which differently sized particles break as differently sized particles
take on stress. Moreover, it is suggested that entropy coordinates may also stress path dependency, a feature not present in
conventional indices.

Dynamic Behaviour of a Geotechnical Seismic Isolation System with Rubber-Sand Mixtures to Enhance Seismic Protection

Juan Bernal-Sanchez, John McDougall, Marina Miranda-Manzanares, and
1 more author

A Geotechnical Seismic Isolation (GSI) system is proposed in this study based on the use of Rubber-Soil mixtures (RSm)
to facilitate the benefits of dynamic soil-foundation structure interaction. The latter is possible due to the lower stiffness
and greater capacity to dissipate energy of RSm. However, the research done on RSm has been limited to the element scale context.
In this study, the dynamic response of a modified soil foundation has been investigated by adding soft zones comprising RSm. A
1g shaking table was used to apply a sequence of sinusoidal excitations to a soil-lumped mass system. The results have shown
that the rubber addition results in a reduction of the amplification at frequencies higher than the system natural frequency.
This change in the dynamic response is due to the shift in the natural frequency and the dampening of the peak output accelerations.
This study shows thus that an alternative design consideration with bagged soft zones, adjacent to the soil foundation, can offset
the incoming disturbances and hence could protect both new and existing constructions.

Some Notes on Granular Mixtures with Finite, Discrete Fractal Distribution

Emőke Imre, István Talata, Daniel Barreto, and
9 more authors

Periodica Polytechnica Civil Engineering, Jan 2022

The ground is a natural grand system; it is composed of myriad constituents that aggregate to form several geologic and biogenic systems. These systems operate independently and interplay harmoniously via important networked structures over multiple spatial and temporal scales. This paper presents arguments and derivations couched by the authors, to first give a better understanding of these intertwined networked structures, and then to give an insight of why and how these can be imitated to develop a new generation of nature-symbiotic ground engineering techniques. The paper draws on numerous recent advances made by the authors, and others, in imitating forms (e.g. synthetic fibres that imitate plant roots), materials (e.g. living composite materials, or living soil that imitate fungi and microbes), generative processes (e.g. managed decomposition of construction rubble to mimic weathering of aragonites to calcites), and functions (e.g. recreating the self-healing, self-producing, and self-forming capacity of natural systems). Advances are reported in three categories of Materials, Models, and Methods (3Ms). A novel value-based appraisal tool is also presented, providing a means to vet the effectiveness of 3Ms as standalone units or in combinations.

Editorial: Themed issue on numerical methods of large strain deformation in geotechnical engineering

Daniel Barreto, Matteo O. Ciantia, and Ashraf Osman

Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, Oct 2021

Some cases of backward erosion/liquefaction piping are dscribed. These distinguish between usual
sand boils and the ‘fast’ piping, the - possibly dynamic liquefaction induced – breach. The latter happens in a
matter of minutes, whereas in the former emergency response measures can be effective.

Examination of saturated hydraulic conductivity using grading curve functions

Emőke Imre, Ágnes Bálint, Laszlo Nagy, and
6 more authors

In 6th International Conference on Geotechnical and Geophysical Site Characterization, Sep 2021

In a previous research program 74 artificial soil mixtures of natural fluvial soils were prepared in 4 series of measurements for falling
head permeability testing, differing in d10. The conclusions drawn from the original investigations were as follows: the k showed a decreasing
tendency with the increase of the uniformity index U for each series of measurements and increasing tendency with d10. In this research these are
used (i) to test the value of the grading entropy parameters in case of non-precise grading curve measurement with missing fines, (ii) to correlate the
usual grading curve parameters like d10, d30, d5 and d60 or their ratios and the grading entropy parameters, (iii) to validate some
existing permeability – grading curve equations and to elaborate some new permeability – grading curve relationships partly with entropy parameters partly
with the usual parameters. For these aims, series I to IV have been started to be reevaluated, some specific surface formulae were derived. Some additional,
literature data were also considered. The very first results are presented here. According to the results, the fine fractions significantly influenced the
value of the entropy parameters. The base entropy So showed strong relationship with and parameters like d10, d30, d5 and d60. The
entropy increment ∆S showed a monotonic increasing relationship with U. The specific surface parameter (containing density info) showed the best
relationship with k out of the d-type parameters like d10 or harmonic mean dh. The original conclusions were reformulated in terms of S0 and
∆S. It was also concluded that those parameters that are based on all measured data are more precise than the single diameter values in the
k-regressions. The specific surface parameter is the best in this repect probably since containing density information, too.

Housing Construction On Peatland: Phase 1 Report

Juan Bernal-Sanchez, John McDougall, Gabriela Medero, and
2 more authors

The economic development and social resilience of communities in rural Scotland is being hampered by a shortage of affordable
housing. Nationally, about 23,000 new homes per year are needed, whilst in the year up to October 2018, only 18,000 were built (BBC, 2019). The
remoter rural areas of Scotland are spacious enough to offer considerable scope for affordable housing development and generally have lower land
values but other factors including challenging ground conditions, notably peat, can make development in these areas economically unviable and
environmentally unsustainable. Scottish peatlands are predominantly blanket bogs, the largest of which are found in the Highlands and Western
Isles. Around 20% of Scotland’s land surface area is covered by blanket bogs alone, which in turn is about 15% of the global total for this
habitat (Bruneau and Johnson, 2014). In response to the shortage of affordable housing and the incidence of peat soils, this project sought to:
-Identify the scale of the shortage,
-Recognise the significance of construction on the peat from a multidisciplinary standpoint,
-Compare, existing and innovative options for foundation design on peat, so as to lessen the magnitude of the construction challenge.
The three bullet points correspond to the first three work packages of this project. A fourth work package will allow for dissemination of findings.

Chapter 4 - A guide to modeling the geotechnical behavior of soils using the discrete element method

This article describes the discrete element method (DEM) for the modeling of the geotechnical behavior of soils. Emphasis is made on a
description of the algorithms and capabilities of the method rather than on the implementation details and equations which are well described in
the existing literature. This article aimed to provide a quick guide for practitioners/researchers with some knowledge about the method, but without
the time to implement and/or modify their own code. As such, plenty of references are provided, which may be used to explore further detail. Apart
from a brief description of the requirements for realistic DEM simulations, a section on practical advice, which could only be gained with years of
experience, is discussed.

2020

The Saturated Hydraulic Conductivity Of 2-Fraction Granular Soils And The Internal Stability

Emőke Imre, Zsombor Illes, Ágnes Bálint, and
5 more authors

The four grading entropy coordinates can be used for soil classification on the basis of grain size and the grading curve shape (similarly
e.g., to the diameter values). The grading entropy coordinates give information on several basic Physics features of soil like minimum dry density,
internal structure and degree of degradation for natural soils. Therefore, assumingly, using them, good permeability k regression relations can be
elaborated. In this work some laboratory tests are made for saturated permeability on fractally distributed sand mixtures (which are mean grading
curves with predetermined composition). After the first stage of the measurement it is found that, the results indicate that the preciseness is better
if only the data of non-segregating, internally stable mixtures are used, indicating the importance of selecting non-segregating mixtures in laboratory
tests.

2019

Grading entropy coordinates and criteria for evaluation of liquefaction potential

Daniel Barreto, J. Leak, V. Dimitriadi, and
3 more authors

In 7th International Conference on Earthquake Geotechnical Engineering, Oct 2019

Several methods are commonly used for the evaluation of liquefaction potential in soils. These include criteria based on SPT and CPT tests,
shear wave velocity measurements and gradation limits, amongst others. This study applies the concept of grading entropy coordinates that enables
plotting any particle size distribution (PSD) as a single coordinate pair in a Cartesian plane, whilst also considering the entire range of
the grading curve. This is in contrast to descriptors such as the mean particle diameter (d50) and the coefficients of uniformity and curvature,
cu and cc, respectively, which ignore the fines content as well as the presence of coarser particles within the PSD. Considering 62 gradings identified
as liquefiable soils in existing studies it was demonstrated that the grading entropy coordinates are a potentially effective tool to
assess liquefaction potential. Furthermore, it was postulated that existing internal stability criteria in terms concept of grading entropy
coordinates may also be used as a framework for the evaluation of liquefaction potential.

Grading curves and internal stability

E. Imre, Daniel Barreto, I. Talata, and
5 more authors

In MAFIOK 2019 - Matematikát, Fizikát És Informatikát Oktatók, Oct 2019

The measured grading curve is an empirical distribution function, a step function. This is considered here as a discrete
distribution with fixed statistical cells. In the grading entropy theory it is characterized by the relative entropy resulting in
two sets of entropy coordinates. These first and second grading entropy coordinates classify well the grading curves and are
statistically more soundly based in terms of information content than the approximate quantile type parameters used at present. In
the theoretical and experimental work on the grading entropy coordinates, the physical content of the parameters are analysed. The results can
be summarized as follows. The first entropy parameter seems to be a continuous internal stability measure. The second one allows the
definition of a unique, mean grading curve with finite fractal grain size distribution for fixed value of the first parameter. The first
parameter is related to internal structure, proven here by DEM tools. It is shown by Math tools that the probability of a stable state of the grading
entropy theory is very low. The generally occurring stable states in the nature are originated from the degradation which is deterministic.
The internal stability of the engineering structures can be characterized by grading entropy.

Preliminary study on the relationship between dry density of sands and the grading entropy parameters

E. Imre, J. Lorincz, P.Q. Trang, and
10 more authors

In The XVII European Conference on Soil Mechanics and Geotechnical Engineering, Oct 2019

Some earlier data were analysed, searching the relation between the minimum dry density emax and the two grading entropy parameters (mean log diameter and fraction number characteristic). The data were split into two components. The first data component – constituting the major part of the density – was the linear function of the mean log diameter, the second one followed the shape of the entropy diagram and it was about the same for the constant vale of the mean log diameter. The density– in terms of normalized the mean log diameter– was maximal around at the point where internal structure changed.

Reanalysis of some in situ compaction test results

E. Imre, J. Lorincz, P.Q. Trang, and
5 more authors

In The XVII European Conference on Soil Mechanics and Geotechnical Engineering, Oct 2019

Brandl (1977) presents the grading curve results of an investigation of particle disintegration of natural sandy gravel and crushed stone bedding courses due to in situ compaction and the action of construction traffic in different civil engineering applications. The work also includes a method to predict the disintegration behaviour of these materials, on the basis of simple laboratory investigations. The concerning compaction are presented in terms of grading curves. The entropy coordinates were computed for the grading curves, before and after compaction. According to the results, the base entropy So, which is a kind of dimensionless mean log diameter, is decreasing during compaction, the entropy increment is increasing according to the entropy principle. Since the grading curve difference and entropy path depend on the grain material and the compaction work, the latter can be characterized if the formers are known

A note on seismic induced liquefaction

E. Imre, J. Lorincz, P.Q. Trang, and
6 more authors

In The XVII European Conference on Soil Mechanics and Geotechnical Engineering, Oct 2019

Any particle size distribution can be characterized by two parameter pairs (derived from the statistical entropy formula of discrete
distributions) more effectively than simple diameter values (i.e., d50). The first entropy parameter is a continuous internal stability measure.
The second one allows the definition of a unique, mean grading curve. In this paper the seismically-induced liquefaction is examined on the basis
of the case study of Kobe where gravel and silty sand contained gradings were liquefied. The entropy parameters and the internal stability criterion
of the grading entropy theory indicated that the liquefied soils were internally unstable, while other criteria did not indicate possible
liquefaction.

Use of Compaction Grouting as Ground Improvement Technique in Compressible Solid Waste Landfill

G. Tsitsas, V.E. Dimitriadi, D. Barreto, and
1 more author

In The XVII European Conference on Soil Mechanics and Geotechnical Engineering, Oct 2019

Ground improvement methods are increasingly being used as means
to control settlements and improve the shear strength of foundation soils. The compaction grouting (CG) method is a ground improvement method that is used as means to mitigate or even remediate excessive settlements in existing structures. The use of this method causes minimum disturbance to the structures; therefore, it is an appropriate application for those structures. The objective of this publication is to investigate the advantages and limitations of CG as a repair solution in situations where the foundation soil is composed of very compressible solid waste landfill material. The investigation is conducted by means of a case study that includes a 40.000 square meter (m2) commercial centre founded on a previous compressible material and subjected to excessive differential settlements. It includes description of the installation as well as monitoring during and after construction of 1800 CG columns, each having a depth of 15 meters. The data collected from the monitoring systems are used to determine the rate, pressure and volume of injected grout required to achieve the target amount of densification of the foundation soil for a selected treated area.

X-ray tomography of sand-rubber mixtures

Joana Fonseca, A. Riaz, and Daniel Barreto

In International Conference on Tomography of Materials and Structures Australia, Oct 2019

The behavior of sand-rubber mixtures is controlled by the mechanisms taking place at the grain scale. Here, we use a mixture of shredded tire
and a silica sand with similar grain sizes to investigate granular behavior under one-dimensional compression. A mini-oedometer operating inside an X-ray
scanner was used to assess the evolution of the microstructure under loading and unloading. New insights are presented on the development of the contact
surfaces between sand and rubber and the evolution of the void space.

Experimental assessment of stiffness and damping in rubber-sand mixtures at various strain levels

J Bernal-Sanchez, J Mcdougall, D Barreto, and
4 more authors

In Earthquake Geotechnical Engineering for Protection and Development of Environment and Constructions - Silvestri & Moraci (Eds), Oct 2019

The dynamic properties of shredded rubber-soil mixtures (ShRm), comprising a sub-rounded quartz sand combined with small rubber shreds at
0, 10, 20, 30% by mass, were investigated. Testing ranged from small strain, in resonant column apparatus, to large strain, in cyclic triaxial, all
at a frequency of 1 Hz with mean stress equal to 100 kPa. As observed by other workers, the shear stiffness of rubber soil mixtures decreases both (i)
with rubber content and (ii) with shear strain. In contrast, increases in damping ratio are smallest at higher rubber contents. Shear modulus reduction
behaviour for ShRm are shown to fit well for all percentage rubber contents, the functional form put forward by Darendeli (2001). Damping ratio was
well-fitted by Darendeli up to a shear strain of about 0.2%, after which the variable trend shown by ShRm has been adjusted using the expression
proposed by Phillips & Hashash (2009).

The geoengineering approach to the study of rivers and reservoirs

Patrick W.M. Corbett, Amanda Owen, Adrian Hartley, and
4 more authors

This volume contains contributions for two meetings held to explore the links between geoscience and engineering in rivers and reservoirs (surface and subsurface). The first meeting was held in Brazil and as a result the volume contains many contributions from Brazil. The second was held in Edinburgh and produced contributions from modern rivers in the US, India and Scotland. The geological record from Carboniferous to Recent is represented. A range of outcrop techniques are presented along with statistical techniques used to identify patterns in the time series and spatial sense. The book is intended to cover the cross-disciplinary interest in rivers and their sediments and will interest geologists, geomorphologists, civil, geotechnical and petroleum engineers, government agencies.

Particle–scale interactions and energy dissipation mechanisms in sand–rubber mixtures

J. Fonseca, A. Riaz, J. Bernal-Sanchez, and
5 more authors

Sand−rubber mixture (SRm) behaviour is affected by rubber content (RC) while dissipation in sands is caused by inter-particle sliding.
Dissipation in SRm is as, or more significant than in sands. However, the mechanisms of dissipation in SRm are not well understood. In this study,
one-dimensional compression tests on sand samples with RC of 0, 15, 30, 45 and 100% by mass were performed on a standard oedometer. In addition,
a SRm with RC of 30% was tested on a mini-oedometer placed inside an X-ray scanner and three-dimensional images of the internal structure of the
material were acquired at three stages during loading and unloading. Image analysis was used to infer particle-scale measurements and provide
experimental evidence to help explaining the energy dissipation mechanisms for SRm. It is postulated here that energy dissipation in these mixtures
is dominated by inter-particle sliding at initial stages of loading, but once rubber particles fill the void spaces between the sand, deformation
and dissipation mechanisms are dominated by the deformation of the rubber particles.

2018

Dynamic behaviour of shredded rubber soil mixtures

Juan Bernal-Sanchez, John McDougall, Daniel Barreto, and
2 more authors

In 16th European Conference on Earthquake Engineering, Oct 2018

Residential buildings in high population density areas are seismically vulnerable to the action of major seismic events. The high cost and
technical difficulties related to the use of advanced seismic isolations systems precludes its installation to low-to-medium rise buildings in the
developing world. The environmental issues attributed to the stockpiling of scrap tires and its use as tire derived fuel has led research to explore
viable recycling solutions in civil engineering projects. Several authors have proposed a novel seismic isolation system by mixing recycled rubber
tires with sand particles. However, research to date has been mainly focused on the dynamic properties of this mixture in the low-to-medium strain
range at a specific loading cycle. This paper has studied the dynamic properties in the medium-to-large shear strain amplitude (0.05%-1%) of
shredded rubber-soil mixtures (ShRm). The influence of the rubber percentage, size ratio, shear strain amplitude and number of cycles have been
evaluated. The shear modulus decreases at larger rubber percentages and strain amplitudes. The damping ratio has been found to increase by adding
10% rubber but it decays at greater rubber percentages. The results show that the dynamic properties of ShRm are affected by the number of cycles
at the strain amplitude assessed in this paper. However, the addition of up to 30% of shredded rubber particles increase significantly the resilience
of sand particles against cyclic loading leading to a reduction in the stiffness and damping degradation.

Optical Fiber Sensor Design for Ground Slope Movement Monitoring for Railway Safety Operations

Daniel Hook, William Laing, Abdelfateh Kerrouche, and
2 more authors

Scour and slope instability are a major issue in keeping the railway structures safe and operational. Conventional measurement techniques do not allow real-time monitoring of slope movement and/or are time/resource consuming. Novel fiber optic technology could be utilized to continuously monitor variations in movement in the slopes along embankments adjacent to railway tracks so that early detection and warnings can be issued to avoid catastrophic events, as well as to enhance maintenance operations. To this end, a fiber optic Bragg grating-based sensor network embedded into a steel bar has been utilized to evaluate its feasibility to be installed in a railway embankment for slope movement monitoring. The paper highlights the initial laboratory results followed by a discussion on the practical implementation of the sensor system.

The influence of particle-size distribution on critical state behavior of spherical and non-spherical particle assemblies

M. D. Jiang, Z. X. Yang, D. Barreto, and
1 more author

This paper presents an investigation into the effects of particle-size distribution on the critical state behavior of granular materials using
Discrete Element Method (DEM) simulations on both spherical and non-spherical particle assemblies. A series of triaxial test DEM simulations examine the
influence of particle-size distribution (PSD) and particle shape, which were independently assessed in the analyses presented. Samples were composed of
particles with varying shapes characterized by overall regularity (OR) and different PSDs. The samples were subjected to the axial compression through
different loading schemes: constant volume, constant mean effective stress, and constant lateral stress. All samples were sheared to large strains to
ensure that a critical state was reached. Both the macroscopic and microscopic behaviors in these tests are discussed here within the framework of the
anisotropic critical state theory (ACST). It is shown that both OR and PSD may affect the response of the granular assemblies in terms of the
stress-strain relations, dilatancy, and critical state behaviors. For a given PSD, both the shear strength and fabric norm decrease with an increase
in OR. The critical state angle of shearing resistance is highly dependent on particle shape. In terms of PSD, uniformly distributed assemblies mobilize
higher shear strength and experience more dilative responses than specimens with a greater variation of particle sizes. The position of the critical state
line in the e-p’ space is also affected by PSD. However, the effects of PSD on critical strength and evolution of fabric are negligible. These findings
highlight the importance of particle shape and PSD that should be included in the development of constitutive models for granular materials.

Influence of grading on shear stiffness - the significance of accurate description of particle size distributions

A new method was elaborated to characterize the breakage properties of rocks. A crushing test was suggested and parallel tests were performed on sand-pairs with different parent rocks, using identical initial gradings. The data were analysed using the grading entropy theory, the grading curve variation was represented in the entropy diagram (with a coordinate uniquely related to the mean log diameter). The results with various rocks with the same conditions indicated the same en-tropy path, only the speed was different. Based on this, a new testing method can be suggested. As a by-product of the result, it is shown that the breakage path and the internal stability of soils seem to be linked. The discontinuity of the normalisedentropy path at the appearance of some finer fractions drifts out the normalised entropy path from the unstable part of the diagram. A second consequence is the explanation why fractal distribution with fractal dimension n

2017

The influence of particle geometry and the intermediate stress ratio on the shear behavior of granular materials

Y. H. Xie, Z. X. Yang, D. Barreto, and
1 more author

The behavior of granular materials is very complex in nature and depends on particle shape, stress path, fabric, density, particle size distribution, amongst others. This paper presents a study of the effect of particle geometry (aspect ratio) on the mechanical behaviour of granular materials using the Discrete Element Method (DEM). This study discusses 3D DEM simulations of conventional triaxial and true triaxial tests. The numerical experiments employ samples with different particle aspect ratios and a unique particle size distribution (PSD). Test results show that both particle aspect ratio (AR) and intermediate stress ratio (b=(σ2’-σ3’)/(σ1’-σ3’)) affect the macro-and micro-scale responses. At the macro-scale, the shear strength decreases with an increase in both aspect ratio and intermediate stress ratio b values. At the micro-scale level, the fabric evolution is also affected by both AR and b. The results from DEM analyses qualitatively agree with available experimental data. The critical state behaviour and failure states are also discussed. It is observed that the position of the critical state loci in the compression (e-p’) space is only slightly affected by aspect ratio (AR) while the critical stress ratio is dependent on both AR and b. It is also demonstrated that the influence of the aspect ratio and the intermediate stress can be captured by micro-scale fabric evolutions that can be well understood within the framework of existing critical state theories. It is also found that for a given stress path, a unique critical state fabric norm is dependent on the particle shape but is independent of critical state void ratio.

2016

The Influence of Particles’ Aspect Ratio on the Shear Behaviour of Granular Materials

The mechanical response of granular material depends both on the material properties (e.g. stiffness, anisotropy, permeability, etc.) and particle geometry (shape, roughness, etc.). This paper presents a study of the effect of particle shape (i.e. aspect ratio) on the mechanical behaviour of a granular assembly using DEM (discrete element method). In this study, the numerical simulations employ samples with different particle aspect ratios but identical particle size distribution (PSD). Conventional triaxial compression DEM simulations are carried out under both ‘drained’ and ‘undrained’ (constant volume) conditions. The shear behaviour of the assemblies and the evolution of their microstructure under shearing are examined in detail. At the macroscopic level, the test results show that the particle aspect ratio has a significant effect on the stress-strain curve, peak strength, dilatancy characteristics and critical state behaviour. In particular, the samples with lower aspect ratios can lead to higher peak/residual shear strengths, and higher angles of shearing resistance. The critical state occurs at a higher position in a void ratio versus mean normal stress plot for lowest particle aspect ratio. The results from numerical analysis compare reasonably well with the available experimental data. At the microscopic level, the fabric evolution is greatly affected by the aspect ratio, and the critical state fabric is also examined.

Revisiting the particle size effects in centrifuge modelling

S Nadimi, J Fonseca, R N Taylor, and
1 more author

In The 3rd European Conference on Physical Modelling in Geotechnics, Oct 2016

Geotechnical centrifuge modelling provides an opportunity to examine novel and complex events in a well-controlled and repeatable environment. While grain interaction and contact dynamics are considered in centrifuge modelling, the soil is treated as a continuum, consistent with standard geotechnical analysis. In the last four decades, particle size effects have been normally approached by the ratio of median particle diameter to critical dimension of modelled structure. The current study considers the response of a granular medium in a centrifuge model by coupling physical tests and equivalent discrete element simulations. The response of a strip footing on uniformly graded glass ballotini is investigated. This is chosen as the sample characteristics can be accurately replicated in a discrete element simulation. Particle size distribution, gravity and footing width are scaled in the context of model-the-model technique and the sensitivity of the bulk response to rapid increase in stress level is explored. This will help establishing the link between the micro phenomena and the macro response and contribute towards improving geotechnical design. The paper describes the work conducted to overcome challenges related to physical modelling including particle mixing, sample preparation, image analysis, and loading apparatus.

2015

Micromechanical insight into the undrained instability of granular materials: deformation characteristics of geomaterials.

Daniel Barreto, Luis Felipe Prada-Sarmiento, and Alfonso Mariano Ramos-Canon

In 6th International Symposium on Deformation Characteristics of Geomaterials, Oct 2015

There is no agreement between experimental researchers whether the point where a granular material responds with a large change of stresses,
strains or excess pore water pressure given a prescribed small input of some of the same variables defines a straight line or a curve in the stress space.
This line, known as the instability line, may also vary in shape and position if the onset of instability is measured from drained or undrained triaxial
tests. Failure of granular materials, which might be preceded by the onset of instability, is a subject that the geotechnical engineers have to deal with
in the daily practice, and generally speaking it is associated to different phenomena observed not only in laboratory tests but also in the field.
Examples of this are the liquefaction of loose sands subjected to undrained loading conditions and the diffuse instability under drained loading
conditions. This research presents results of DEM simulations of undrained triaxial tests with the aim of studying the influence of stress history and
relative density on the onset of instability in granular materials. Micro-mechanical analysis including the evolution of coordination numbers and fabric
tensors is performed aiming to gain further insight on the particle-scale interactions that underlie the occurrence of this instability. In addition to
provide a greater understanding, the results presented here may be useful as input for macro-scale constitutive models that enable the prediction of the
onset of instability in boundary value problems.

An overview of research activities and achievement in Geotechnics from the Scottish Universities Geotechnics Network (SUGN)

A Leung, I X Anastasopoulos, C E Augarde, and
24 more authors

In 16th European Conference on Soil Mechanics and Geotechnical Engineering, Oct 2015

Design of geotechnical systems is often challenging as it requires the understanding of complex soil behaviour and its influence on field-scale performance of geo-structures. To advance the scientific knowledge and the technological development in geotechnical engineering, a Scottish academic community, named Scottish Universities Geotechnics Network (SUGN), was established in 2001, composing of eight higher education institutions. The network gathers geotechnics researchers, including experimentalists as well as centrifuge, constitutive, and numerical modellers, to generate multiple synergies for building larger collaboration and wider research dissemination in and beyond Scotland. The paper will highlight the research excellence and leading work undertaken in SUGN emphasising some of the contribution to the geotechnical research community and some of the significant research outcomes.

2014

Significance of DEM input parameters on the modelling of low strength soft rock mechanical behaviour.

In this paper 2D DEM simulations of biaxial compression tests on low strength soft rocks are presented. These aimed to replicate the mechanical
behaviour of the materials, in particular the effect of interlocking between particles using assemblies with both a realistic and a reduced particle size
distribution. A contact model that incorporates tensile strength and cohesive resistance of bonded particles is used in both simulations to demonstrate that
the macro-scale behaviour obtained is not as observed in experimental tests if realistic PSDs are used. This is found to be a consequence of inaccurate
contact models when real particle sizes are input. Hence the results of existing DEM research, in particular the micro-scale observations which are supposed
to explain the unique features of the mechanical behaviour of structured soils, may be questionable.

2013

Use of DEM and elastic stability analysis to explain the influence of the intermediate principal stress on shear strength

C. O’Sullivan, M.A. Wadee, K.J. Hanley, and
1 more author

One interesting aspect of soil response is the sensitivity of the mechanical behaviour to the intermediate principal stress. In this study, a
fundamental mechanism that explains the influence of the intermediate stress ratio (b) on soil shear strength is proposed. Prior experimental, numerical
and analytical studies have indicated that soil failure occurs when the strong force chains that transmit stress through the material buckle. These strong
force chains are networks of contacting particles that are relatively highly stressed, and aligned in the direction of the major principal stress
( σ ′ 1 ). The buckling resistance is thought to be determined by ‘weaker’ lateral networks of less-stressed contacting particles that are orthogonal
to the strong force chain orientation. Discrete-element method (DEM) simulations of true triaxial tests show that as b is varied, so too is the relative
support provided by the force chains orientated in the directions of the intermediate and minor principal stresses ( σ ′ 2 and σ ′ 3 respectively). At a
macro scale, the effective axial stiffnesses along these directions vary. The DEM dataset is complex, and so a conceptually simple model is used to assess
the influence of lateral support on the buckling resistance of a single column of connected nodes, analogous to a single force chain. The lateral support
is modelled using linear springs. When the stiffnesses of these springs are selected to reflect the variation in axial stiffness with b observed in the
DEM simulations, the reduction in axial buckling load with b is found to be similar to the reduction in major principal stress with b. When combined, the
DEM data and simple analytical model support a hypothesis that failure under three-dimensional stress conditions is determined by buckling of the strong
force chains. It is the variation in lateral support provided by the force network aligned along the minor and intermediate stress directions that
determines, in part at least, the relation between soil shear strength and b. The data presented provide a conceptually simple framework to justify the
need to consider three-dimensional effects in geomechanical stress–deformation analyses, and may inform future development of constitutive models.

Volumetric consequences of particle loss by grading entropy

J.R. McDougall, E. Imre, Daniel Barreto, and
1 more author

Chemical and biological processes, such as dissolution in gypsiferous sands and biodegradation in waste refuse, result in mass or particle loss, which in turn lead to changes in solid and void phase volumes and grading. Data on phase volume and grading changes have been obtained from oedometric dissolution tests on sand–salt mixtures. Phase volume changes are defined by a (dissolution-induced) void volume change parameter (Λ). Grading changes are interpreted using grading entropy coordinates, which allow a grading curve to be depicted as a single data point and changes in grading as a vector quantity rather than a family of distribution curves. By combining Λ contours with pre- to post-dissolution grading entropy coordinate paths, an innovative interpretation of the volumetric consequences of particle loss is obtained. Paths associated with small soluble particles, the loss of which triggers relatively little settlement but large increase in void ratio, track parallel to the Λ contours. Paths associated with the loss of larger particles, which can destabilise the sand skeleton, tend to track across the Λ contours.

Particle loss and volume change on dissolution: experimental results and analysis of particle size and amount effects

Soil particles may be lost through dissolution, degradation or erosion. Regardless of the process of loss, there follows a change in soil structure both in terms of phase composition and grading. In this paper, the influence of size and amount of particle loss on phase composition at two stresses is investigated. The tests are performed on sand–salt mixtures, loaded in a modified permeation oedometer and subsequently dissolved. Changes in overall volume and void ratio are presented. Two significant observations about the volumetric consequences of particle loss can be made. First, overall volume changes are directly related to the amount of dissolved particles and to a lesser extent, the size of particle lost. Second, particle loss leads to an increase in void ratio; the magnitude of the increase is related to the amount of dissolved particles but appears not to be sensitive to either the size of particle lost or the pre-dissolution void ratio. Based on the observed response and a dissolution-induced void change parameter, the influence of different mechanisms of volume change is discussed. Tests were performed at two different vertical stresses with no discernible influence on void ratio change.

Quantifying stress-induced anisotropy using inter-void constrictions

Thomas Shire, Catherine O’Sullivan, Daniel Barreto, and
1 more author

In particulate geomechanics it is common to quantify fabric anisotropy using contact and particle orientations. Measurement of void anisotropy is less common, most likely owing to the difficulties associated with defining individual voids. Here a Delaunay tessellation-based approach is applied to measure anisotropy of the inter-void constriction orientations. This new measure of fabric anisotropy was capable of identifying stress-induced anisotropy in discrete-element modelling true triaxial simulations with spherical particles. A relationship is established between the constriction orientations, the macro-scale principal stress directions and the micro-scale contact normal orientations.

2012

Effect of particle loss on soil behaviour

Darren Kelly, John McDougall, and Daniel Barreto

In 6th International Conference on Scour and Erosion, Oct 2012

Soil particle loss can result in strength and volume reductions which are difficult to predict. This paper investigates the
influence of the removal of fractions of selected particle sizes under different confining pressures. The mass lossprocess was reproduced by the
dissolution of selected salt particle sizes and fractions from uniform Leighton Buzzard sand. The dissolution tests were performed in a triaxial cell
customised to allow circulation of pore-fluid thereby allowing the dissolution/removal of the salt fraction. Test results from previously conducted
oedometric dissolution tests and subsequent triaxial dissolution tests all show increases in void ratio. From the triaxial tests, a reduction in shear
strength with increasing ductility was observed. Volumetric and strength behaviour were found to be related to the particle size and fraction material
removed while shear-wave measurements obtained pre- and post-particle removal indicate significant changes in small-strain stiffness.

The use of electronic voting systems to enhance deep learning.

Daniel Barreto

In Shaking the Foundations of Geo-engineering Education, Jul 2012

The present paper introduces a technology-enhanced teaching method that promotes deep learning.
Four stages that correspond to four different student cohorts were used for its development and to analyse
its effectiveness. The effectiveness of the method has been assessed in terms of examination results as well as
results obtained from class response system software statistics. The evidence gathered indicates that the method
developed is very effective and its implementation is straightforward. Furthermore, its success in achieving
results seems to be independent of the skills and/or experience of the lecturer.

The influence of inter-particle friction and the intermediate stress ratio on soil response under generalised stress conditions

Previous research studies have used either physical experiments or discrete element method (DEM) simulations to explore, independently, the influence of the coefficient of inter-particle friction (μ) and the intermediate stress ratio (b) on the behaviour of granular materials. DEM simulations and experiments using photoelasticity have shown that when an anisotropic stress condition is applied to a granular material, strong force chains or columns of contacting particles transmitting relatively large forces, form parallel to the major principal stress orientation. The combined effects of friction and the intermediate stress ratio upon the resistance of these strong force chains to collapse (buckling failure) are considered here using data from an extensive set of DEM simulations including triaxial and true triaxial compression tests. For all tests both μ and b affected the macro- and micro-scale response, however the mechanisms whereby the force chain stability was improved differ. While friction clearly enhances the inherent stability of the strong force chains, the intermediate stress ratio affects the contact density and distribution of orthogonal contacts that provide lateral support to the force chains.

2011

Exploring the effects of stress history on the drained and undrained cyclic behaviour of granular materials.

Daniel Barreto

In 5th International Conference on Geotechnical Earthquake Engineering (5-ICEGE), Jul 2011

This paper presents the results of 3D DEM simulations of granular materials subject to cyclic loading. While both the drained and undrained conditions are considered, the effects of depositional history and consolidation stress history on the stress-strain response are specifically evaluated. It is demonstrated that the different stress histories have a significant effect on soil response and that such effects can be attributed to differences in the initial particle arrangement (fabric).

2010

Numerical and experimental investigation into the behaviour of granular materials under generalised stress states

Daniel Barreto

Jan 2010

PhD thesis. Imperial College London. Available at http://hdl.handle.net/10044/1/11332

It is well recognized that the macro-scale response of soils is anisotropic in terms of strength, stiffness, permeability, etc. The source of this anisotropy is thought to be an anisotropy of the material itself. This anisotropy can be quantified using statistical methods if DEM numerical simulations or advanced experimental techniques are used. The anisotropic response of soil has been analyzed by many researchers in terms of the fabric tensor, which provides a measure of the orientation of the contacts between particles. Although many approaches for the quantification of the evolution of soil fabric have been used, they have not been previously compared to assess their effectiveness to describe fabric changes. A direct comparison of different methods of fabric quantification is presented in this paper based on the results from DEM simulations under different stress paths and the suitability of each of these methods is discussed. The results highlight the need for more accurate methods and/or approaches to accurately describe the evolution of fabric anisotropy in granular materials

Radial periodic boundaries for axi-symmetric DEM simulations: development, implementation and validation.

Catherine O’Sullivan, Liang Cui, and Daniel Barreto

In International Conference on Particle-Based Methods, Particles 2009, Jan 2009

Discrete Element Method (DEM) simulations ofelement tests cam provide significant insight into the micro-mechanics of soil response. It is well established that soil behaviour is strongly dependant on the initial density. Generation of particulate assemblies for three-dimensional DEM analyses must therefore allow for void ratio control. In this paper, different specimen generation approaches for DEM analyses are discussed. A methodology for the generation of assemblies of spherical particles with a specified initial density and stress state is presented. The effects of the different preparation methods on the specimen fabric are then considered in detail. For isotropic consolidation, it is shown that varying the coefficient of inter-particle friction allows control of the specimen void ratio at a specified confining stress. Simulations of anisotropic consolidation, from an initial isotropic stress state, to a final state where sigma(3) = K(0)sigma(1) indicated that the specimen void ratio and fabric are relatively insensitive to the intermediate stress path, provided an intermediate stress along the K(0) line was attained.

Evolution of soil fabric and its interpretation using different methods.

Daniel Barreto

In British Geotechnical Association (BGA) Young Geotechnical Engineers’ Symposium, Jan 2008

Different methods to study the evolution of fabric anisotropy are presented. DEM simulations on assemblies of spheres subjected to different stress paths using a three-dimensional periodic cell are used for the analysis of these methods. The links between soil fabric and macro-scale behaviour are also discussed.

DEM simulations of granular materials involving principal stress rotation.

Daniel Barreto, Catherine O’Sullivan, and Lidija Zdravkovic

In Inaugural International Conference of the Engineering Mechanics Institute - EM’08, Jan 2008