The micro-mechanical blueprint of earth materials

Franz-Josef Ulm 1 and Younane Abousleiman 2 ..................................................... 1
Khalid A. Alshibli, Ph.D., PE., ................................................................................ 4
Dr Simon Joseph Antony ...................................................................................... 7
Alaa K. Ashmawy ................................................................................................. 9
Béatrice Baudet ................................................................................................. 10
Antonio Bobet.................................................................................................... 12
Malcolm Bolton ................................................................................................. 14
Ronaldo I. Borja ................................................................................................. 15
Lis Bowman ........................................................................................................ 17
Dr Fraser Bransby .............................................................................................. 18
Jonathan D. Bray, Ph.D., P.E. ............................................................................. 19
Howard W Chandler .......................................................................................... 21
Yi Pik Helen Cheng ............................................................................................. 22
Jason T. DeJong .................................................................................................. 23
Pierre Delage ..................................................................................................... 25
Richard Finno ..................................................................................................... 27
Marte S. Gutierrez ............................................................................................. 29
Jie Han, Ph.D., P.E. ............................................................................................. 31
Roman D. Hryciw ............................................................................................... 32
Tomasz Hueckel ................................................................................................. 34
Adrian Hyde ....................................................................................................... 36
Mingjing Jiang .................................................................................................... 38
Matthew R. Kuhn ............................................................................................... 40
Ning Lu ............................................................................................................... 42
Dr Glenn McDowell............................................................................................ 44

James K. Mitchell ............................................................................................... 46
Robert L. Mokwa ............................................................................................... 48
David Muir Wood .............................................................................................. 50
Yukio Nakata ...................................................................................................... 52
Tang-Tat (Percy) Ng ........................................................................................... 53
Dr. Catherine O’Sullivan..................................................................................... 55
Milan Patel ......................................................................................................... 56
Dunja Perid ......................................................................................................... 57
Amy L. Rechenmacher ....................................................................................... 59
Dr. J. Carlos Santamarina ................................................................................... 61
Radhey S. Sharma .............................................................................................. 62
Beena Sukumaran .............................................................................................. 65
Dr. Colin Thornton ............................................................................................. 67
Gioacchino (Cino) Viggiani, ................................................................................ 68
Linbing Wang, Ph.D., P.E. ................................................................................... 71
D. Ian Wilson ...................................................................................................... 73
Mourad Zeghal................................................................................................... 75

1 Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge,
Massachusetts 02139
2 The PoroMechanics Institute, Mewbourne School of Petroleum & Geological
Engineering, and School of Civil Engineering and Environmental Science, University of
Oklahoma, 100 East Boyd, Norman, Oklahoma 73019
The Micro-Mechanical Blueprint of Earth Materials
Despite their ubiquitous presence as sealing formations in hydrocarbon bearing
reservoirs i affecting many fields of exploitation, the mechanical behavior of
shale is still an enigma that has deceived many decoding attempts from
experimental ii and theoretical sides iii . Sedimentary rocks, such as shale, are
made of highly compacted clay particles of sub-micrometer size iv,v , nanometric
porosity and different mineralogy. Currently, all attempts have failed to break
such complicated natural composite materials down to a scale where this earth
material no longer change from one horizon to another and identify the
fundamental unit of material invariant properties (the mechanical ‘blueprint’).
Based on the statistical analysis of massive nano-indentation data and multi-
scale modeling of different sedimentary rocks and in particular shale, we
identify some very first material invariant properties. We argue that they are
the result of inter-mineral surface properties and characteristic packing
densities, which are almost not affected by much stiffer mineral properties vi,vii .
These observations hold for most natural porous composites: bones viii ,
concretes ix , sandstones, etc., which are the focus of the GeoGenome�
Project x , an international research effort, that aims at ‘breaking the code’ of all
natural composite materials.

predicted Cij [GPa]
Nanofabric Nanofabric Microfabric Microfabric Macrofabric
Macrofabric
50
40
30
20
10
0
0 10 20 30 40 50
measured Cij [GPa]
shale1
shale2
shale3
shale 4
shale 5
shale 6
shale J
shale K
shale C
Figure 4: Model-based prediction of shale elasticity: The top panels show the multiscale
micromechanics model. The nanofabric is captured by a continuous isotropic
solid phase and oriented pores, the textured microfabric by a layered composite, and
the macrofabric by a matrix-silt inclusion composite. The bottom panel shows the
predictive capabilities of the model for nine different shale materials of different
mineralogy, porosity and silt inclusion fractions. For each shale material, the graph
compares predicted vs. measured values of the five elasticity constants of the
transversely isotropic material.

i) Jones, L.E.A. & Wang, H.F. Ultrasonic velocities in Cretaceous shales from
the Williston basin. Geophysics, 46: 288-297 (1994).
ii) Hornby, B. Experimental laboratory determination of the dynamic elastic
properties of wet, drained shales. Journal of Geophysical Research,
103(B12): 29945-29964 (1998).
iii) Hornby, B., Schwartz, L. & Hudson, J. Anisotropic effective medium
modeling of the elastic properties of shales. Geophysics, 59(10): 1570-1583
(1994).
iv) Mitchell, J. Fundamentals of soil behavior. J. Wiley & Sons, New York
(1993).
v) Bennett, R.H. , O'Brien N.R. & Hulbert, M.H. Determinants of clay and shale
microfabric signatures: Processes and mechanisms. In R. Bennett, W.
Bryant, M. Hulbert (eds), Microstructure of fine grained sediments: from
mud to shale, Springer-Verlag, New York, Chapter 2, 5-32 (1991).
vi) Mavko, G., Mukerji, T. & Dvorkin, J. The Rock Physics Handbook.
Cambridge University Press, UK (1998).
vii) Wang, Z., Wang, H. & Cates, M.E. Effective elastic properties of solid clays.
Geophysics, 66(2): 428-440 (2001).
viii) Hellmich, Ch., Ulm, F.-J. & Dormieux, L. Can the diverse elastic properties
of trabecular and cortical bone be attributed to only a few tissue-
independent phase properties and their interactions? - Arguments from a
multiscale approach. Biomechan Model Mechanobiol 2, 219–238 (2004).
ix) Constantinides, G. & Ulm, F.-J. The effect of two types of C-S-H on the
elasticity of cement-based materials: Results from nanoindentation and
micromechanical modeling. Cement and Concrete Research 34, 67–80
(2004).
x) Abousleiman, Y. and Ulm, F.-J. The GeoGenome� Industry Consortium,
Funded Proposal at the University of Oklahoma, 2005-2007.

Joint Assistant Professor
Dept. of Civil & Environmental Engineering
Louisiana State University & Southern University
Baton Rouge,LA 70803, USA
Tel. 1-225-578-9179 | Fax Tel. 1-225-578-8652
Email: Alshibli@lsu.edu
http://www.cee.lsu.edu/facultyStaff/Alshibli_Khalid
� Non-destructive evaluation of geomaterials
� Terrestrial and planetary soil mechanics
� Constitutive behavior of soils
� Applications of Computed Tomography (CT) to characterize micro-fabric of
geomaterials
1. Batiste, S. N., Alshibli, K. A., Sture, S., and Lankton, M. (2004) “Shear Band
Characterization of Triaxial Sand Specimens Using Computed Tomography”
ASTM, Geotechnical Testing J., 27 (6): 568-579.
2. Alshibli, K. A. and Alsaleh, M. (2004) “Characterizing Surface Roughness
and Shape of Sands Using Digital Microscopy”, ASCE, J. of Computing in
Civil Engineering, 18 (1): 36-45.
3. Alshibli, K. A., Batiste, S. N., and Sture, S. (2003) “Strain Localization in
Sand: Plane Strain Versus Triaxial Compression”, ASCE, J. of Geotechnical &
Geoenvironmental Engineering, 129 (6): 483-499.
CT rendering of 6 mm spherical beads with holes

SEM of two Ottawa sand particles
CT image of a sand specimen

Astronaut Kalpana Chawla performs MGM experiment during Shuttle Columbia
mission
Mars rover Spirit, an artist's rendition (courtesy of NASA files)

University of Leeds
Dr S. Joseph Antony is a lecturer at the Institute of Particle Science and
Engineering, University of Leeds. His research expertise is in the area of
computational particulate mechanics. He has wide experience with advanced
numerical modelling techniques, such as Discrete Element Method (DEM),
Finite Element Method (FEM) and Boundary Element Method (BEM), applied to
discrete and continuum materials subjected to mechanical loading. His current
research focus is on the micromechanical modelling of powders and grains
using DEM, establishing the fundamental link between the single-particle
properties (measured from experiments) and the bulk behaviour of powders
subjected to mechanical and electrical loading conditions. His research works
have been published in several reputed international journals and referred
conference proceedings. A few examples include studies on the force
transmission characteristics [1], shear deformation characteristics of soft and
hard granular materials [1-3], size effects in granular media [4], flow
characteristics of cohesive grains [5], shape effects in granular assemblies [6,7]
and the micromechanical behaviour of particulate agglomerates [8,9].
Currently, SJA co-investigates with his colleagues on several fundamental, but
industrially significant projects. Examples include modelling studies on the
dispersion characteristics of nano-particles (GR/R66623), packing
characteristics of nuclear powders (CO1-08), predicting the bulk characteristics
of powders using single particle properties (BLK), scale up studies of shear
mixer granulators (GR/S25029/01), mechatronic modelling of particles
(Ref.23913) supported by Royal Society, London, and FEM studies on designing
optimum process conditions for the fabrication of economically viable polymer
wires (supported by EPSRC). The companies SJA collaborates with include ICI,
Unilever, P&G, BNFL and Borax Europe, Hosokawa-Micron, Pfizer, Bridon and
DuPont (UK).
SJA actively participates in the activities of granular materials community in U.K
and abroad. He is currently a member of EPSRC College, U.K IChemE Particle
Technology Subject Group Committee, ASME Applied Mechanics Division-
Materials Division Joint Committee on Constitutive Equations and European
Society of Computational methods in Science and Engineering. Currently, SJA
serves as a member of peer reviewers in his area of research for several
international journals. He has also served as a lead guest editor for the JL.
Granular Matter (2004) and for the special publication (book) by the Royal
Society of Chemistry, London on the ‘Advances in Granular Materials:
Fundamentals and Applications’ (2004). The book chapters were contributed
by thirteen world-class research groups working in the area of particle
technology. He has recently won the prestigious MIT Young Research
Fellowship Award for Exemplary Research in Computational Mechanics. He was

awarded by the IChemE as an Example of Outstanding Achievement in U.K
Particle science and Technology in 2002.
1. S.J. Antony (2001) ‘Evolution of force distribution in three dimensional
granular media’., Physical Review E, American Physical Society, 63(1),
011302
2. C. Thornton and S.J. Antony (1998) ‘Quasi-static deformation of particulate
media’., Philosophical Transactions of the Royal Society of London,
Series:A, 356(1747), 2763-2782
3. C. Thornton and S.J. Antony (2000) ‘Quasi-static deformation of a soft
particulate system’., Powder Technology, 109, 179-191
4. S.J. Antony and M. Ghadiri (2001) ‘Size Effects in a Slowly Sheared Granular
Media’, Journal of Applied Mechanics, American Society of Mechanical
Engineers , 68(5), 772-775.
5. R. Moreno, S.J. Antony and M. Ghadiri (2004) ‘Analysis of flowability of
cohesive powders using distinct element method’, Powder Technology (In
print)
6. S.J. Antony and M.R. Kuhn (2004) ‘Influence of particle shape on the
interplay between contact signatures and particulate strength’,
International Journal of Solids and Structures, 41, 5863-5870
7. S.J. Antony, R. Momoh and M.R. Kuhn (2004) ‘Biaxial compression of oval
particulates: Micromechanical study’, Jl. Computational Materials Science
, 29, 494-498
8. R.Moreno, M. Ghadiri and S.J. Antony (2003) ‘Effect of the Impact Angle on
the breakage of agglomerate: a numerical study using DEM’, Powder
Technology , 4622, 1-6
9. M. Ghadiri , S.J. Antony, R. Moreno and Z. Ning, (2001) ‘Granular Powders
and Solids: Insights from Numerical Simulations’, Powders & Solids:
Development in handling and Processing Technologies, Proceedings of the
Royal Society of Chemistry, W.Hoyle(ed.), London, 70-81

University of South Florida
4202 E. Fowler Ave., ENB 118
Tampa, FL 33620
Tel: (1) 813-974-5598
Email: ashmawy@eng.usf.edu
Website: http://www.eng.usf.edu/~ashmawy/research/dem_angular.html
My work currently focuses on the quantification and modeling of granular
particle shapes, and their influence on the mechanical response. The work is
approached from the perspectives of measurement and quantification of
natural particle shapes, development of meaningful particle shape descriptors,
and incorporation of those shapes within 2D and 3D Discrete Element Models.
At the experimental level, a collaborative study with Rowan University, funded
by the National Science Foundation, is currently underway to look at methods
to quantify the geometry of particles in 3D and to relate 2D and 3D shape
descriptors. The objective is to devise simple procedures for describing the 3D
shapes using 2D measurements. As part of the study, a database comprising
voxels of granular particles collected from various locations is being developed.
At the numerical modeling level, new tools are being developed to incorporate
a library of particle shapes within the discrete element code, PFC. The process
is being automated for both 2D and 3D versions of the software. Some of the
issues our group has faced include the influence of the contact model and
surface roughness on the mechanical response of the granular assembly. These
issues are not directly addressed in our current study but are of significant
importance. Other topics for possible discussion at the Workshop include fluid-
mechanical coupling at the micro-scale, and the ability of micro-scale models to
simulate macro-systems.
1. Sukumaran, B., and Ashmawy, A.K. (2003), “Influence of Inherent Particle
Characteristics on Hopper Flow Rate,” Powder Technology, Vol. 138, No. 1,
pp. 46-50.
2. Sallam, A.M., Ashmawy, A.K.., and Runkles, B.D. (2004), “Experimental
validation of modeling irregular particle shapes using DEM,” Numerical
Modeling in Micromechanics via Particle Methods, Proc 2 nd Intl PFC Symp,
Kyoto, Japan, pp. 363-372.
3. Ashmawy, A.K., and Sallam, A.M. (2005), “Discrete Element Modeling of
Natural Particles,” Accepted for publication, 11 th Intl Conf of IACMAG,
Turin, Italy, June 2005.

Department of Civil & Environmental Engineering
University College London
Gower Street, London WC1E 6BT, UK
Tel: 020 76792262
b.baudet@ucl.ac.uk
My research interest lies in modelling the behaviour of natural clays. I have
approached the problem from the macro-scale end. I have for example
developed a numerical model to simulate the effects of structure and de-
structuring on these clays. I have tried to use parameters that have a physical
meaning and can all be derived from simple triaxial tests on reconstituted and
intact samples. Until the micro-scale is understood, developing models within
existing frameworks for natural soils seems to be the only way to use
parameters that have a physical meaning. The Sensitivity Framework suggested
by Cotecchia & Chandler (2000), which establishes a correspondence between
the effects of structure on strength and yield stress up to peak, forms a good
base from which to develop models for structured clays. One of my current
interests is to try to extend it to states post-peak.
There are still many unknown to the structure-related behaviour of clays, and
the model is based on some assumptions for which there is experimental
evidence, needed at the micro-level, is not available. The first assumption is
that in most soils there are stable elements of structure arising from fabric that
cannot be removed even at very large strains. The second assumption is that
both plastic volumetric and shear strains play a role in the de-structuring of
clays, of similar proportion. Finally, there is the assumption, adopted by most
models developed for structured soils, that the shapes of the boundary
surfaces for the natural and reconstituted soils are the same, and remain the
same during de-structuring. That implies that at any point during de-structuring
the degree of structure can be measured as the ratio between the sizes of the
surfaces for the natural and reconstituted soils. It also implies that the
Sensitivity Framework should be valid post-peak. I have started investigating
this last point by the means of simple shear tests. Results so far show that the
assumption may not be erroneous.
I have more recently been involved in research on the time-dependent
behaviour of clays. The research investigates the effects of strain rates on the
strength and stiffness of kaolin and of London clay, with the underlying aim to
include them in the model described above. So far the outcome of the research
shows that not only strain rate but also the acceleration of strain has an effect
of the subsequent behaviour of clays.

1. Baudet B.A. & Ho E. On the behaviour of deep-ocean sediments.
Géotechnique 54, No. 9, 571-580
2. Baudet B.A. & Stallebrass S.E. A constitutive model for structured clays.
Géotechnique 54, No. 4, 269-278
3. Baudet B.A. & Stallebrass S.E. (2003). Modelling effects of fabric and
bonding in natural clays. Proceedings of International Workshop on
Geotechnics of Soft Soils (IWGSS); Noordwijkerhout, The Netherlands, Sept.
2003

Associate Professor of Civil Engineering
Purdue University, School of Civil Eng.
550 Stadium Mall Drive, West Lafayette, IN, USA.
1-765-494-5033
bobet@purdue.edu
Dr. Bobet’s interests lie on fracture phenomena in compression, at the micro-,
meso- and macro-scales. Initiation and propagation of shear cracks, and crack
coalescence are some of the topics that have been the focus of his research.
Two problems are explored in the workshop: crack initiation and coalescence in
compression, and slip initiation along frictional discontinuities.
Crack coalescence. Crack initiation, propagation and coalescence have been
investigated by loading specimens of a brittle material with pre-existing
fractures in uniaxial and biaxial compression. Both open and closed (frictional)
fractures had been investigated. Specimens were prepared and tested with
two, three, and sixteen fractures. The research showed that results from
specimens with two fractures could be readily extrapolated to specimens with
multiple fractures. It was found that only a limited number of coalescence
patterns existed. The types of coalescence could be correlated with the
fracture geometry and were independent of the number of fractures. Also,
coalescence was possible through any number of combinations of tensile and
shear cracks. Observations at the micro-scale showed that the surface of
tensile cracks was characterized by unbroken crystals and the damage area
around a tensile crack was about 10 to 20 �m, which was comparable to the
size of a crystal. The damage area around a shear crack was about 100 �m,
about one order of magnitude larger than for a tensile crack. An array of
microtensile cracks was observed at an angle with the direction of shearing
(approximately 45 o ) which produced columns of crystals. With further shear
the columns break, and as a result, the surface of the shear crack was coated
with broken crystals, which at a low magnification were observed as powder.
En-echelon steps on the surface of a shear crack caused dilation in the two
directions perpendicular to the direction of shear (Mode I and III components),
which produced a discontinuous contact between the surfaces of the crack (i.e.
asperities).
Slip initiation. Discontinuities in brittle materials are typically non-persistent
and show non-homogeneous frictional characteristics. Slip may not occur
simultaneously along the entire surface of the discontinuity. In fact slip may
nucleate at weak regions and propagate towards stronger regions.
Investigation of the onset of slip along a non-homogeneous frictional surface
has been carried out by testing in biaxial compression gypsum specimens with
a pre-existing non-homogeneous discontinuity. The experiments showed that

slip started first in a weak area and progressed towards the strong area with
increasing load. Once slip had reached the strong area, a sharp contact was
created between the area that had slipped (weak) and the area that had not
(strong). At the contact, a large concentration of stresses occurred which was
treated within the fracture mechanics framework. Results from the tests
showed that the critical energy release rate, GIIC, was not a material property. It
increased with normal stress and its magnitude depended on the frictional
characteristics of the surface and on the displacement required to decrease the
frictional strength from peak to residual. It was also found that the slip required
for debonding was much smaller than that required to reduce friction from
peak to residual.
1. Bobet, A. (2000). The Initiation of Secondary Cracks in Compression.
Engineering Fracture Mechanics, Vol. 66, No. 2, pp. 187-219.
2. Sagong, M. and Bobet, A. (2002). Coalescence of Multiple Flaws in a Rock-
model Material in Uniaxial Compression. International J. of Rock Mechanics
and Mining Science. Vol. 39, No. 2, pp. 229-241.
3. Mutlu, O., and Bobet, A. (2005). Slip Initiation on Frictional Fractures.
Engineering Fracture Mechanics Journal, Vol. 72, No. 5, pp. 729-747.

Cambridge University
Malcolm Bolton graduated in engineering from Cambridge University in 1967,
and also holds an MSc in structural engineering from Manchester University
and a PhD in soil mechanics from Cambridge University. He started his
academic career as a lecturer at UMIST in 1970 where he took up geotechnical
centrifuge model testing, and published his undergraduate textbook “A Guide
to Soil Mechanics”. He returned to Cambridge in 1980 where he now holds the
post of Professor of Soil Mechanics. In 2001 he became the first Director of the
Schofield Centre for Geotechnical Process and Construction Modelling.
He has worked on a wide variety of geotechnical research projects including
earth retaining walls, slope stability, reinforced soils, deep excavations,
tunnelling, pile driving, and offshore foundations and pipelines. He has 160
research publications – for details see:
http://www-civ.eng.cam.ac.uk/geotech_new/geotech.htm.
He is Chairman of ISSMGE TC35 Geomechanics of Particulate Materials, and is
on the Scientific Committee of the Powders and Grains Conference, reflecting a
lifelong interest in the fundamentals of granular materials.

Stanford University
E-mail: borja@stanford.edu
We are interested in bridging the gap between the micro-scale (particle scale)
and macro-scale (specimen scale) descriptions in discrete granular materials.
We are currently pursuing a meso-scale modeling approach (larger than the
particle scale but smaller than the specimen scale). This approach is motivated
primarily by the current advances in laboratory testing capabilities that allow
accurate measurements of material imperfection in the specimens, such as X-
Ray Computed Tomography (CT) and Digital Image Processing (DIP). Our
approach relies on nonlinear continuum mechanics and finite element analysis;
however, we analyze the specimen as a structure and impose measured meso-
scale inhomogeneities (from CT and using DIP) in the form of spatial density
variation in the specimens. The ultimate goal of the project is to predict the
internal displacements in samples of granular soils experiencing shear banding,
which are measured in the laboratory using a technique known as Digital Image
Correlation (DIC). This work is a collaborative effort between Amy
Rechenmacher’s group at USC and my group at Stanford, with funding coming
from Dr. Fragaszy’s NSF Program. The USC group is responsible for conducting
X-Ray CT tests and producing quantitative data using DIP for input into a finite
element program; the Stanford group is responsible for developing the
mechanical finite element model and performing numerical simulations. The
mechanical model we have developed for this purpose is now completed and is
described in the following paper:
Borja, R.I. and Andrade, J., Critical state plasticity, Part VI: Meso-scale finite
element simulation of strain localization in discrete granular materials,
Computer Methods in Applied Mechanics and Engineering, in review for the
John Argyris Memorial Special Issue, 2005, manuscript and other related work
may be downloaded from the following address:
http://www.stanford.edu/~borja/pub/2004.htm.
My interest in the Micro-Geomechanics workshop lies in the “flow”
perspective. The term “flow” may be interpreted in different ways. Right at
the moment of loading, discrete granular materials (such as sands) exhibit
“plastic flow” due to particle re-arrangement (an irreversible process).
However, I am interested in the flow process occurring at very large strains,
such as that occurring inside a shear band. Specifically, there are two types of
flow processes along a shear band that I am interested in:

(a) Shear bands forming through granular soils – here, the micro-mechanical
processes involve mineral particle rolling and sliding. The thickness of the
physical shear band is not well defined – some particles in the rigid zone may
be carried along by the moving particles inside the band, while some particles
inside the band may get trapped in the rigid zone. Discrete element models
has the potential to simulate the phenomena numerically. DIC has the potential
to capture the internal displacements in the samples on the meso-scale level.
(b) Faulting in granular rocks – this process occurs when rough surfaces are
brought into contact. Contact processes control the friction and wear of
surfaces and regulate the formation of fault gouges. Experimental
investigations, including imaging surface contacts, have been done in the past.
Shearing along the fault zone is controlled by a different mechanism than in
granular soils, since rolling is restricted to comminuted particles. The evolution
of the size and population of surface contacts is of utmost interest. State- and
velocity-dependent friction laws have been developed in the past to enable the
description of the plastic flow within the fault. Work is currently underway at
Stanford University to incorporate these friction laws into strong discontinuity
finite element models.

Cambridge University
Website: http://www-civ.eng.cam.ac.uk/geotech_new/geotech.htm
(click on “post-doctoral” then, “E. T. Bowman”)
1. Static to flow to static behaviour at micro-macro level in granular
materials: with particular reference to behaviour of:
� Long run-out rock avalanches (“sturzstroms”)
o Role of dynamic fragmentation
o Role of acoustic fluidization
� High-speed erosive debris flows
o Role of fines in random-perturbation liquefaction
o Role of particle size and bed fabric in erosion
2. Ageing and creep of granular materials: with particular reference to:
� Displacement pile set-up
� Ageing of blast-densified and vibro-compacted fills
In both areas of interest, work is mostly based on physical modelling and
laboratory experimental approaches.
(papers relating to 1 st area of interest are in preparation!)
1. Bowman, E.T. & Soga, K. (accepted) “Mechanisms of set up of
displacement piles in sand: Laboratory creep tests” Canadian Geotechnical
Journal
2. Bowman, E.T. & Soga, K. (2003) "Creep, ageing and microstructural change
in dense granular materials" Soils & Foundations 43 (4), 107-117.
3. Bowman, E.T., Soga, K. & Drummond, T.W. (2001) "Particle shape
characterisation using Fourier descriptor analysis" Geotechnique 51 (6),
545-554.

University of Dundee, Scotland
www.dundee.ac.uk/civileng/research/geotech.htm
I’m an impostor at this meeting: most of my research interests are in the area
of foundations, slopes and soil-structure interaction (i.e. not micro-mechanics).
I use numerical methods (mainly fem), analytical techniques and centrifuge
modelling to study these topics. I stress micro-mechanics in my teaching and
have some student research projects investigating element level behaviour and
the role of micro-mechanics. The following are areas in my research where I
consider micro-mechanics may be important:
Shear band propagation
I have three areas of research in which shear band propagation is important:
earthquake fault propagation, slip planes (and their reinforcement) in soil
slopes, and the upheaval buckling of offshore pipelines. It is also important
along soil-inclusion interfaces in soil reinforcement. In all these, the key
question is how and at what displacement a shear band/slip plane is formed
within the soil. This normally occurs somewhere near the development of peak
load. Can continuum mechanics principles be used when this deformation
mode is reached and will it help us predict displacements required to failure?
Should we use micro-mechanics principals to predict shear plane mobilisation
and ‘strains’ in the shear plane? Study is being done primarily by PIV analysis of
soil deformations in physical model tests.
Scaling in centrifuge modeling
Clearly when reducing the linear dimension of centrifuge models (but keeping
the stress and strain constant wrt the prototype) the particle size is not scaled
if the same soil is used. Previous researchers suggest that similitude conditions
exist as long as there are a significant number of particles (i.e. > 20) across the
smallest characteristic length. However, there is a danger (first pointed out by
Sloan, 1973?) that shear plane propagation distances and continuum
displacements consequently mobilise at different times because of scaling
disparities.
Element testing
Earlier work looked at soil deformation during cyclic loading (in the resonant
column) and the effects of frequency on its behaviour. More recent work has
involved studying deformation in the shear box apparatus (particularly when
reinforced by inclusions) and the role of particle behaviour in soil compression.

University of California, Berkeley, USA
Email: bray@ce.berkeley.edu
DEVELOPING ENGINEERING PROCEDURES TO EVALUATE EARTHQUAKE
SURFACE FAULT RUPTURE
Recent earthquakes have reminded the profession of the potentially
devastating effects of earthquake surface fault rupture on engineered systems.
My emphasis has been on describing how ground movements associated with
surface faulting affect engineered systems, and then in developing analytical
procedures to capture the phenomenon. Analytical procedures can be
employed to evaluate the hazardsassociated with surface faulting and to
develop reasonable mitigation measures. However, advances are limited by the
continuum nature of the finite element and finite difference methodologies
typically employed.
My research interests in discrete element methods resulted from my desire to
attack this problem from a more realistic and innovative approach. Discrete
element methods capture the inherent discontinuous nature of particulate
media, and it is an ideal analytical procedure for evaluating geotechnical
problems involving soil failure.
Although my initial goal was modeling earthquake fault rupture propagation
through soil, my work has been largely at the micromechanical level of soil
response. If one cannot capture the response of a simplified analogy of
granular material that is measured in the laboratory (i.e. steel and glass rods
and balls), how can one hope to capture the complex phenomenon of
earthquake surface fault rupture.
1. Thomas, P.A. and Bray, J.D., “Capturing the Nonspherical Shape of Granular
Media with Disk Clusters,” Journal of Geotechnical and Geoenvironmental
Engineering, American Society of Civil Engineers, Vol. 125, No. 3, pp. 169-
178, 1999.
2. Bray, J. D. “Developing Mitigation Measures for the Hazards Associated
with Earthquake Surface Fault Rupture,” in A Workshop on Seismic Fault-
Induced Failures – Possible Remedies for Damage to Urban Facilities,
Research Project 2000 Grant-in-Aid for Scientific Research (No. 12355020),
Japan Society for the Promotion of Science, Workshop Leader, Kazuo
Konagai, University of Tokyo, Japan, pp. 55-79, January 11-12, 2001.

3. O’Sullivan, C. and Bray, J.D., “Relating the Response of Idealized Analogue
Particles and Real Sands”, Proceedings of the Numerical Modeling in Micro-
mechanics via Particle Methods, First International PFC Symposium, Nov.
2002.
4. O’Sullivan, C., Bray, J. D., and Riemer, M. F., “The Influence of Particle
Shape and Surface Friction Variability in Particulate Media Response,”
Journal of Engineering Mechanics, American Society of Civil Engineers, V.
128, No. 11, Nov. 2002, pp. 1182-1192.
5. O’Sullivan, C., Bray, J.D., and Li, S. “A New Approach for Calculating Strain
for Particulate Media," International Journal for Numerical and Analytical
Methods in Geomechanics, Vol. 27(10), July 2003, pp. 859-877.
6. O’Sullivan, C., Bray, J. D., and Riemer, M. F., “An Examination of the
Response of Regularly Packed Specimens of Spherical Particles Using
Physical Tests and Discrete Element Simulations,” Journal of Engineering
Mechanics, ASCE, V. 130, No. 10, Oct. 2004, pp 1140-1150.

Engineering, University of Aberdeen
Models of the plastic behaviour of granular materials that have corners in the
yield surface have been troubling us since at least the Cam-Clay model. Dealing
with corners has given many computational problems as well as conceptual
ones. The work presented here looks at the results of a simple model of what
might happen when an assembly of deformable granules is compacted and
shows some interesting and surprising features.
The model assumes:
� a smooth rigid-plastic contact law between granules that hardens as the
contact patch flattens; and
� that the contact forces acting on differently orientated contacts are given
in terms of the global stress state.
The global strain increments are calculated by integrating the contact
deformation over all orientations. This is similar to the classical lower bound
approximation for aggregates of elastic crystals.
For this compactable assembly of granules, in the case of proportional loading
paths up to a constant amount of compaction, a smooth surface was produced
and the flow rule was consistent with a model using an elliptical yield surface
and volume hardening. Where the results surprised me was that by unloading
and then reloading along a different path it was clear that a corner was
produced on the yield surface at a point in stress space where the original
proportional loading path had terminated.
This leaves a conundrum: is there a simple flow rule for a loading increment out
from the corner not in the directional of the original loading path? The answer
seems to be yes, but it looks like anisotropic elasticity, not isotropic plasticity.
R. J. Henderson, H.W. Chandler, A.R. Akisanya, C. M. Chandler, & S.A. Nixon,
Micro-mechanical modelling of powder compaction. Journal of the Mechanics
and Physics of Solids v49 (2001) 739-759.

University College London
Discrete Element Method (DEM) is a popular tool in studying the mechanics of
granular soils. Due to the crushable nature of most granular materials, it was
found necessary to involve particle breakage in the simulation procedure. An
element was created with about 400 crushable grains retained by rigid walls so
that localised deformation was not allowed. The DEM grains were formed from
bonded microspheres which tended to interlock in the fashion of rough
irregular particles. Grain breakage could therefore involve either the
detachment of a single microsphere (asperity damage) or splitting. Particle size
distribution curves calculated during various stress paths were similar to those
obtained from real tests.
The theories of soil plasticity following Roscoe, Schofield and others ignored
particle breakage. Recent work (Cheng, et al. 2003, 2004, Cheng 2004) shows,
however, that breakage is central to the elastic-plastic transition of soils.
Breakage also raises the question of the uniqueness of the Critical State Line
which is the starting point for the Cam Clay family of soil plasticity models. The
role of breakage and the definition of Critical States are explored through DEM
simulations.
My research interest is mainly to use DEM to investigate how a change in the
microscopic parameters induced by, for example particle breakage, influence
the macroscopic deformation mechanism of soils.
1. Cheng, Y.P., Nakata Y. & Bolton M.D. 2003. Discrete element simulation of
crushable soil. Geotechnique, 53(7), 633-642.
2. Cheng, Y.P., Bolton M.D. & Nakata Y. 2004. Crushing and plastic
deformation of soils simulated using DEM. Geotechnique, 54(2), 131-141.
3. Cheng, Y.P. 2004. Micromechanical investigation of soil plasticity. PhD
thesis, Cambridge University.

University of Massachusetts Amherst
Phone: 413-545-2639
E-mail: dejong@ecs.umass.edu
WWW: http://geotech.ecs.umass.edu/dejong.html
My research interests and activities include sensors, instrumentation and
monitoring, granular soil and granular-structure interface behavior, and site
characterization. My group’s research approach is generally through science-
based inquiry and applying the knowledge gained to develop practical
engineering solutions. Active topics that align well with the theme of the
workshop (and which I look forward to discussions on) include:
Cyclic Soil-Structure Interface Behavior (topic to be presented at workshop):
We have been exploring and developing framework for the analysis of cyclic
soil-structure interface behavior that is analogous to the critical state concept
for soil shearing. Using Particle Image Velocimetry (PIV) the evolution and
accumulation of volumetric and shear strains in the shear zone adjacent to the
interface have been quantified. By coupling this with global measurements of
displacement and stress an interface critical state framework has been
developed. Results from preliminary tests indicate that the model captures the
observed behavior well and additional testing is underway.
Relation of Particle Breakage under 1-D Compression and Interface Shear:
Our research on cyclic interface shearing has results in a sub-study that is
focused relating the rates and magnitude of particle breakage that occurs
during interface shear. The correlations of interface breakage with 1-D crushing
are being investigated as previous particle breakage research has focused on
the latter testing mode. Interface shear tests have been performed and the
extent of particle breakage has been quantified as a function of the distance
from the interface shear surface. The following trends were observed:
breakage is primarily confined to within 3 mm of interface surface, breakage
increased substantial when cyclic displacement is greater than average particle
diameter, shear direction reversal increases breakage for subrounded particles.
Biological Processes in Soils and Opportunities to Develop Biological
Treatments:
Biological processes are pervasive in the subsurface. Within geotechnical
engineering minimal research has been performed to determine whether
biological processes can be harnessed and used advantageously for
geotechnical applications. With a micro-biology colleague I am investigating
developing light cementation in sands using microbial activity.

1. DeJong, J.T., Randolph, M.F., and White, D.J. (2003) “Interface Load
Transfer Degradation During Cyclic Loading: A Micromechanical
Investigation”, Soils and Foundations, Vol. 43, No. 4, pp. 81-94.
2. Frost, J.D., and DeJong, J.T., and Recalde, M., (2002) “Shear Failure
Behavior of Granular-Continuum Interfaces”, Engineering Fracture
Mechanics, Vol. 69, No. 17, pp. 2029-2048.
3. DeJong, J.T. and Westgate, Z. (2004) “Role of particle crushing at the soil-
structure interface during cyclic loading”, American Society of Civil
Engineers, Engineering Mechanics Conference 2004 Conference, Delaware,
5 p.

Ecole Nationale des Ponts et Chaussees, Paris
delage@enpc.fr
Microstructure of sensitive clays from Eastern Canada
Researches on sensitive clays of Eastern Canada were carried out some time
ago (Delage & Lefebvre 1984) by using both mercury intrusion porosimetry
(MIP) and scanning electron microscopy (SEM) on intact freeze-dried samples
(Sherbrooke sampler). A typical aggregate microstructure was observed in the
samples of medium sensitivity (St = 40-50). Very high sensitivity values (St = 500)
were related to the presence of non clayey small particles (< 2 �m) observed
both in SEM and MIP. It was shown that remoulding did not affect the
aggregates. During oedometer compression, it was observed that pores were
progressively collapsed, in an ordered manner, starting from the larger and
progressively collapsing smaller and smaller pore. This simple mechanism
supposes a brittle nature of the links between aggregates, which is the case in
low plasticity soils.
Mechanisms involved in heavily compacted clays
Results obtained by using X ray diffractometry at low angles on heavily
compacted swelling clays used as possible engineered barriers for nuclear
waste disposal helped for a better understanding of the mechanisms of
swelling. Starting from a high initial suction (>100 MPa), it was confirmed that
hydration occurred by the ordered and progressive placement of layers of
water molecules along the elementary clay sheet layers by layers, up to 4 layers
with simultaneous changes in the constitution of the clay particle (initially
made up of 100-.300 sheets and decreasing down to 10 sheets by separation
one from another). Interestingly, these mechanisms occur at constant levels of
suction (50 and 7 MPa). High stress oedometer tests where controlled suction
changes under constant loads were monitored indeed showed that the
previously described hydration phases correspond to typical macro mechanical
behaviour features, particularly around 7 MPa. The macromechanical
behaviour can hence be linked to some given levels of energy of water (defined
by suction values). A critical assessement on double layer concepts often used
when interpreting swelling can also be derived from theses observations. Other
research concern the effect of adsorbed cations (Na and Ca) on he high stress
compressibility of bentonites (Marcial et al. 2002).

1. Delage P. & Lefebvre G. 1984. Study of the structure of a sensitive
Champlain clay and its evolution during consolidation. Canadian
Geotechnical Journal 21 (1), 21-35.
2. Delage P., Audiguier M., Cui Y.J. & Howat M.D. 1996. Microstructure of a
compacted silt. Canadian Geotechnical Journal, 33 (1), 150-158.
3. Delage P., Howat M. & Cui Y.J. 1998. The relationship between suction and
swelling properties in a heavily compacted unsaturated clay. Engineering
Geology, 50 (1-2) : 31-48.
4. Yahia-Aissa M., Delage P., & Cui Y.J. 2001. Suction-water relationship in
swelling clays. Clay science for engineering, IS-Shizuoka International
Symposium on Suction, Swelling, Permeability and Structure of Clays, 65-
68, Adachi & Fukue eds, Balkema.
5. Loiseau C., Y.J. Cui & P. Delage. 2002. The gradient effect on the water flow
through a compacted swelling soil. Proceedings of the 3nd International
Conference on Unsaturated Soils, UNSAT’2002 (1), 395-400, Recife, Brazil,
Balkema.
6. Cui Y.J, Loiseau C. & Delage P. 2002. Microstructure changes of a confined
swelling soil due to suction controlled hydration. Proceedings of the 3nd
International Conference on Unsaturated Soils, UNSAT’2002 (2), 593-598,
Recife, Brazil, Balkema.
7. Cui, Y.J., Yahia-Aissa, M. and Delage, P. 2002. A model for the volume
change behaviour of heavily compacted swelling clays. Engineering
Geology, vol. 64, 2-3, 233-250.
8. Marcial D., Delage P. & Cui Y.J. 2002. On the high stress compression of
bentonites. Canadian Geotechnical Journal 39, 812-820.

Northwestern University
Secant Shear Modulus, G sec (kPa)
I have interests in Micro-Geomechanics at both the milli-strain and macro-
strain scales. I look for explanations of observed behavior at the microlevel and
look forward to the day when models based on these concepts can be used in
practice. I have done most work of my past work at larger strains when
studying failure processes in soils, and have focused on experiments on
cohesionless soils with emphasis on observing behavior as shear bands develop
and progress.
I have more recently been interested in responses at the milli-strain level. This
work has focused on evaluating the responses of block samples of soft to
medium stiff Chicago glacial clays subjected at very small to operational strain
levels. Some examples of experimental results from drained stress probes on
specimens consolidated to the in situ vertical effective stress are shown below:
80000
60000
40000
20000
0
Mean G BE
Mean G BE =51000 kPa
Anisotropic loading (AL)
Triaxial compression (TC)
Const. p' compression (CMS)
Reduced triaxial compression (RTC)
Anisotropic unloading (AU)
Reduced triaxial extension (RTE)
Const. p' extension (CMSE)
Triaxial extension (TE)
0.0001 0.001 0.01 0.1 1
Triaxial Shear Strain, � sl (%)

Deviatoric Stress q (kPa)
68
67
66
65
64
24.5
CMS
RTC
16.4 15.6 TC
12.3 AL
8.5
AU
RTE
44.9
60.4
CMSE
22.4
Initial Stress State
p'=89.9, q=66.3 kPa
G BE (ave)=51 MPa
88 89 90 91 92
Effective Mean Normal Stress p' (kPa)
TE
G 0.001 (MPa)
1. Finno, R.J. and Rechenmacher, A.,"Effects of Consolidation History on
Critical State of Sand," JGGE, ASCE, Vol. 129 (4), 2003.
2. Finno, R.J., Harris, W.W., Mooney, M.A., and Viggiani, G., "Shear Bands in
Plane Strain Compression of Loose Sand," Geotechnique, Vol 47 (1) 1997.
3. Holman, T., and Finno, R.J., "Maximum Shear Modulus and Incrementally
Nonlinear Soils," Proc., 16th ICSMGE,” to appear, Osaka, Japan, 2005.

Virginia Tech
Nano-Geomechanics: Potential Applications of Nano-mechanics in
Geotechnical Engineering
The aim of the presentation is to bring to the attention of Geotechnical
Engineers the potential of using nanomechanics in characterizing and modeling
of geomaterials over a wide range of scales. Nanomechanics has huge
possibilities in explaining basic materials response such as creep, friction, and
rate and temperature dependency. Also, constitutive models based on
nanomechanics have distinct advantages over phenomological models in
simulating the response of geomaterials under extreme environments. The use
of nanomechanics will also have significant impacts on how we teach
geotechnical engineering. The presentation will give an overview of
nanomechanics and nano-characterization, preliminary results of MD
(molecular dynamics) simulation of rock minerals, and a comprehensive
discussion of potential applications of nanomechanics in geotechnical
engineering.
Rocks are the most ubiquitous and most diverse materials on the earth’s
surface, and their mechanical and fluid transport properties play important
roles in many different fields. The macroscopic behavior of rocks is
conventionally represented by constitutive models which are formulated within
the frameworks of continuum mechanics and are phenomologically established
from element tests. In many cases, model reliability can only be guaranteed
over the range of conditions in which the model is calibrated. Phenomological
models have difficulty in predicting the behavior of rocks under extreme
environments involving large stresses, high temperatures, and extremely slow
(creep) or fast loading.
M
N
M
a
i
a
Figure 1 – Macro, micro and nanoscale components c
c of
n
rocks
o
r
r
s
o
o
c
-
-
a
c
c
l
Rocks consist of constituents at the macro, omicro
and nanoscales (Fig. 1). The
o
e
n
proposed approach for modeling of rock masses involves subdividing rocks into
t
n
its multiscale components. The behaviors of i the minerals forming t an individual
n
i
u
n
u
m
u
u
m

grain and at the contacts between minerals are analyzed at the nanoscale. The
nanoscale response is homogenized and used in a microscopic model of the
rock mass which consists of an assemblage of individual grains and grain
interfaces. The microscopic model is established by analysis of digital images of
rock microstructures. The response of the microscopic model under load is
modeled and another level of homogenization is applied to derive the
macroscopic response. Finally, the macroscopic model is implemented as a
constitutive model which can be used for finite element modeling of boundary
value problems.

Associate Professor, Dept. of Civil, Environmental, and Architectural Engineering,
University of Kansas, 2150 Learned Hall 1530 W. 15th Street
Lawrence, Kansas 66045-7609,
e-mail: jiehan@ku.edu, Tel: (785) 864-3714, Fax: (785) 864-5631
My research interests in micro-geomechanics mainly focus on the numerical
analysis using particle flow code to study the following topics (but not limited
to). Experimental studies are conducted to calibrate or verify numerical
models. Also, I am interested in research collaborations with others in terms of
experimental and numerical studies of micro-geomechanics.
� Soil arching phenomena under static and dynamic loading
� Geosynthetic-soil interactions
� Behaviors of granular piles in soil subjected to vertical loads
� Fracture development in reservoirs due to exploitation of subsurface
resources (such as coalbed methane)
� Coupling of continuum and micromechanics theories in the numerical
analysis

University of Michigan
Soil Image Processing
In the middle 1990s the author’s research efforts were divided between
development of in-situ soil testing methods and laboratory-scale
micromechanics facilitated by optical monitoring of strain fields and the
kinematics of individual soil particles (Hryciw et al., 1997). These disparate
fields of study found common ground with the development of the Vision Cone
Penetrometer (VisCPT) (Raschke and Hryciw, 1997). Continuous collection of
soil images along a vertical sounding prompted the search for image processing
techniques that would produce digital high resolution stratigraphic
characterization of a site.
The earliest attempts sought to deterministically obtain grain size distributions.
Laboratory methods wherein images of non-contacting grains were collected
and pixels of thresholded features (grains) were counted proved highly
successful (Ghalib and Hryciw, 1999). However, the deterministic assessment
of grain sizes from images of grain assemblies was nearly impossible. Attempts
based on particle edge detection requiring sophisticated numerical algorithms
to “complete the missing edges” were only successful in the most ideal cases.
In reality, the large range of grain sizes and the occlusion of particle edges by
other grains rendered deterministic methods unusable.
Greater success was achieved using “first order” statistical methods based on
image texture (Ghalib et al., 2000). The distribution of adjacent gray-scale pixel
values yielded accurate discrimination between fine-grained (higher
homogeneity) and coarse-grained (higher contrast) materials. Thus, in a single
VisCPT log, clay seams and sand lenses, even a few millimeters thick, were
easily identified (Hryciw et al., 2003, Hryciw and Shin, 2004). Unfortunately,
these indices were also sensitive to grain color and illumination. Thus, a
universal correlation between grain size and the textural indices could not be
found.
The problem of non-unique of textual indices – grain size correlations was
overcome by two-dimensional wavelet analysis of soil images (Shin and Hryciw,
2004). A unique relationship was found between the centroid beneath a
normalized spectral energy distribution of gray scale images and the average
number of pixels per grain diameter in an image of relatively uniform grain size.
If image magnification is known, the average image grain size is computed.
Studies are now being extended to images with multiple grain sizes.
One-dimensional wavelet analysis is also being applied, pixel row by pixel row,
to contiguous images of a laboratory sedimented soil columns. While the

esearch is still in its early stages, preliminary results indicate that this imaging
method will be both quicker and yield more accurate grain size distributions
than presently obtained by sieve and, or hydrometer analysis.
1. Ghalib, A.M. and Hryciw, R.D. (1999) "Soil Particle Size Distribution by
Mosaic Imaging and Watershed Analysis," Journal of Computing in Civil
Engineering, Vol. 13, No. 2, pp. 80-87.
2. Ghalib, A.M., Hryciw, R.D. and Susila, E. (2000) "Soil Stratigraphy
Delineation by VisCPT," ASCE Geotechnical Special Publication No. 97
Innovations and Applications in Geotechnical Site Characterizations,
Proceedings of GeoDenver 2000, pp. 65-79.
3. Hryciw, R. D., Raschke, S. A., Ghalib, A. M., Horner, D. A. and Peters, J. F.
(1997) "Video Tracking of Experimental Validation of Discrete Element
Simulations of Large Discontinuous Deformations", Computers and
Geotechnics, Vol. 21, Iss. 3, pp. 235-253.
4. Hryciw R.D., Shin, S. and Ghalib, A.M. (2003) “High Resolution Site
Characterization by VisCPT with Application to Hydrogeology”, Proc. of Soil
and Rock America, the 12 th Panamerican Conference on Soil Mechanics
and Geotechnical Engineering, Vol. 1, pp. 293-298.
5. Hryciw, R.D. and Shin, S. (2004) “Thin Layer and Interface Characterization
by VisCPT”, Proceedings of the Second International Conference on Site
Characterization (ISC'2004), Porto, Portugal, pp. 701-706.
6. Raschke, S.A. and Hryciw, R. D. (1997) "Vision Cone Penetrometer (VisCPT)
for Direct Subsurface Soil Observation", ASCE Journal of Geotechnical and
Geoenvironmental Engineering, Vol. 123, No. 11, pp. 1074-1076.
7. Shin S. and Hryciw R.D. (2004) “Application of Wavelet Analysis to Soil
Mass Images for Particle Size Determination,” ASCE Journal of Computing
in Civil Engineering, Vol. 18, No 1. pp. 19-27.

Duke University
Durham, North Carolina, USA
hueckel@duke.edu
My interest in the microstructural aspects in geomechanics stems from the
current work on thermo- and chemo-mechanical couplings in soil behavior
under various environmental loads. That includes coupling between mineral
dissolution and stress at intergranular contacts as soil compacts under a long
term loading, and often-dramatic changes in permeability in clays when
subjected to changes in pore fluid content (e.g. contamination with
concentrated organic liquids) or changes in pore water salinity and stress.
Other problems include soil cracking induced by desiccation and chemo-
mechanical effects in landslide inception. In all the above examples the
macroscopic response of soil critically depends on physico-chemical
phenomena that occur at specific, isolated locations of the soil microstructure.
For instance, in the question of dissolution of the stressed mineral contacts, the
rate of dissolution is believed to depend, among other variables, on the
amount of new free surface opened as micro-crack walls inside the grain as a
result of plastic damage. Without a possibility of evaluating of this micro-
damage an assessment of the dissolved mass, and then precipitating mass, can
only be indirectly determined as an empirical result. Our ambition is to be able
to link it directly to the chemical reaction and its rate. Three scales are involved
in the process. One is the molecular scale, at which chemical reactions are
established, then is the microscale of the contact configuration, and finally
there is the macroscale of the multiphase continuum. Hence, chemical
variables are mainly defined at molecular scale, while most of mechanical
variables are defined at macro-, or at best micro-scopic scale. A proper
identification and validation of coupling mechanisms between the phenomena
involved is the primary task in the modeling. Because of the nature of chemo-
mechanics such mechanisms are most commonly spanning two or three scales.
Equally challenging task in multi-scale modeling is a proper representation of
the variables at different scales, and their reduction to a common scale. This
issue came very strongly in addressing variable permeability of contaminant
affected, deforming clays, where pore-mode permeability is linked to the fate
of the interplatelet water, while its evolution is constrained by an additional
mass balance law.
Our current objectives comprise a generalization of the principle of interscale
coupling in the chemo-mechanical constitutive modeling of soils, identification
of variables suitable to describe the microstructure and microstructural
mechanisms at other scales, and establishing criteria for validation of multi-
scale couplings. Our current focus comprises the work on desiccation drying
and aging of soils.

1. T. Hueckel, 2004, Coupling Variable Permeability to Strain and Mass
Transfer in Contaminated Clays, Adv. in Comput. and Exp. Eng. and Sci., p.
1186 –1191, ed. Atluri , A., JB Thaddeu, Tech Science Press, Forsyth, GA,
2. T. Hueckel and L.B. Hu, 2004, Chemo-mechanical coupling and damage
enhanced dissolution at intergranular contact; in Num.l Models in
Geomechanics, G.N. Pande and S. Pietruszczak, eds., Balkema, Rotterdam,
349-353
3. T. Hueckel and R. Pellegrini, 2002, Reactive Plasticity for Clays. Part II:
Application to a natural analog of long-term geomechanical effects of
nuclear waste disposal, Engineering Geology, 64, 2-3, 195 – 216
4. T. Hueckel, B. Loret and A. Gajo, 2002, Expansive clays as two-phase,
deformable, reactive continua: concepts and modeling options, in “Chemo-
mechanical coupling in clays: from nano-scale to engineering applications”
edited by C. Di Maio, T. Hueckel and B. Loret, Swets and Zetlinger, Lisse,
The Netherland, 105 - 120
5. T. Hueckel, G. Cassiani, Fan Tao, A. Pellegrino and V. Fioravante, 2001,
Aging of oil/gas bearing sediments, their compressibility and subsidence, J.
Geot. & and Geoenv. Eng. ASCE, 127, 11, 926 – 938
6. T. Hueckel, F. Tao, G. Cassiani and A. Pellegrino, 1999, Reactive plasticity
for geological materials with a double structure evolving during aging, in
Constitutive Laws for Engineering Materials, 4 th Int. Conference, RPI, Troy,
NY, edited by R.C. Picu and E. Krempl, 383 –387.
7. T. Hueckel, M. Kaczmarek and P. Caramuscio, 1997, Theoretical
Assessment of Fabric and Permeability Changes in Clays Affected by
Organic Contaminants, Canadian Geotechnical Journal, 34, 4, 588 - 603

University of Sheffield
Adrian Hyde is a chartered engineer who graduated from the University of
Nottingham where he went on to research into the cyclic loading of soils and
was awarded a doctorate in 1974. He has taught at the Universities of
Loughborough, Bradford and since 1997 as a senior lecturer and then reader at
Sheffield.
In the early 1980's problems with piled foundations in offshore carbonate
sediments led him to develop an interest in the fundamental generic
characteristics of crushable soils. He initiated joint research with universities in
Japan studying the characteristics of crushable sands which showed that a
study of these soils leads to a better understanding of the fundamental
mechanical characteristics of all soils. This led to the development of research
programmes on the seismic liquefaction of crushable fills and the cyclic loading
of clays and silts related to seismic liquefaction and post-earthquake
settlements.
A regular visitor to Japan he is a Visiting Professor at Yamaguchi University, has
authored over 40 papers with Japanese colleagues, and given over 30
presentations often in Japanese at 9 Japanese universities. Contacts with the
Japanese construction industry led to EPSRC and industry funded research on a
new rapid load pile testing method to improve the quality control and testing
of foundations.
He is leading an EPSRC funded multidisciplinary research programme on the
application of micro-mechanics to the in-situ preservation of archaeological
artefacts. He is also a fluent Italian speaker and the tutor responsible for
European student exchanges and in 2000 he was appointed as a Visiting
Professor at Trento University in Italy.
1. Yasufuku, N. and Hyde, A.F.L. (1995) "Pile end-bearing capacity in
crushable sands" Geotechnique V45 No. 4 pp. 663-676
2. Hyodo, M., Hyde, A.F.L., and Aramaki, N. (1998) "Liquefaction of crushable
soils" Geotechnique 48, No. 4, 527-543.
3. Nakata, Y., Hyde, A.F.L., Hyodo, M. and Murata, H., (1999) "A probabilistic
approach to sand crushing in the triaxial test" Geotechnique 49, No. 5,
567 - 583

4. Nakata, Y., Hyodo, M. Hyde, A.F.L., Kato, Y and Murata, H. (2001) "
Microscopic particle crushing of sand subjected to high pressure one
dimensional compression" Soils and Foundations, Journal
of the Japanese Geotechnical Society, 41, No1, 69-82.
5. Brown, M., Anderson, W. and Hyde, A. (2004), " Statnamic testing of model
piles in a clay calibration chamber" International Journal of Physical
Modelling in Geotechnics, Vol.4, No.1, pp.11-24.

Nottingham Centre for Geomechanics,
School of Civil Engineering,
University of Nottingham, U.K.
e-mail: Mingjing.Jiang@nottingham.ac.uk
Micro-Geomechanics - the Macrostrain and the Millistrain Perspectives
1. Jiang MJ, Harris D, Yu H-S. Kinematic models for non-coaxial granular
materials: Part I: theories. Int. Journal for Numerical and Analytical
Methods in Geomechanics, 2005; 29(7): (in press)
2. Jiang MJ, Harris D, Yu H-S. Kinematic models for non-coaxial granular
materials: Part II: evaluation. Int. Journal for Numerical and Analytical
Methods in Geomechanics, 2005; 29(7): (in press)
3. Jiang MJ, Yu H-S, Harris D. A Variable Linking Microscopic to Macroscopic
Granular Mechanics. The Powders & Grains’05, Stuttgart, Germany, July
18-22, 2005. (in press)
4. Higo Y, Oka F, Jiang MJ and Fujita Y. Effects of transport of pore water and
material heterogeneity on strain localization analysis of fluid-saturated
gradient-dependent viscoplastic geomaterial. Int. Journal for Numerical
and Analytical Methods in Geomechanics, 2005; 29(5): 495-523.
5. Jiang MJ, Harris D, Yu H-S. Rotation-rate in the Harris kinematic equations
for post-failure flow granular materials. International Workshop on
Prediction and Simulation Methods in Geomechanics, ATHENS, Greece,
October 14 - 15, 2003. pp.129-132.
6. Jiang MJ, Shen ZJ. A structural suction model for structured clays.
Proceedings of 2nd International Conference on Soft Soil Engineering,
Nanjing, China, 1996. pp.221-240.
7. Jiang MJ, Shen ZJ. An artificial-preparation of structured collapsible loess
and its behaviour in oedometer test. The Proceedings of 2 nd International
Conference on Unsaturated Soils. Beijing, China, 1998, pp.374-378.
Micro-Geomechanics - Unusual Material and Unusual Behavior
1. Jiang MJ, Leroueil S, Konrad JM. Yielding of microstructured geomaterial
by DEM analysis. Journal of Engineering Mechanics, ASCE, 2005 (in press)
2. Jiang MJ, Yu H-S, Harris D. A discrete modelling of micro-structured
geomaterials incorporating bond rolling resistance. The 11 th Int. Conf. of
IACMAG, June 19-24, 2005, Turin, Italy. (in press)

3. Jiang MJ, Konrad JM., Leroueil S. An efficient technique to generate
homogeneous specimens for DEM studies. Computers and Geotechnics.
2003, 30 (5): 579-597.
4. Jiang MJ, Leroueil S, Konrad JM. DEM study of microstructured soil. 55 th
CSCE-ASCE conference, Hamilton, Ontario, Canada, 2002, pp.313-320.
5. Jiang MJ, Leroueil S., Konrad JM. Insight into strength functions in
unsaturated granulate by DEM analysis. Computers and Geotechnics, 2004;
31(6): 473-489.
6. Jiang MJ, Harris D. Generalized effective stress in unsaturated granulate by
DEM analysis. Int. Conf.: From Experimental Evidences Towards Numerical
Modelling of Unsaturated Soils, Weimar, Germany, September 18 th -19 th ,
2003, Volume II, pp.201-214.
7. Jiang MJ, Shen ZJ, Adachi T and Hongo T. Microanalysis on artificially-
prepared structured collapsible loess. Chinese Journal of Geotechnical
Engineering, 1999, 21(4): 486-491.
8. Jiang MJ, Shen ZJ. Microanalysis on shear band of structured clays. Chinese
Journal of Geotechnical Engineering. 1998, 20(2): 102-108.

University of Portland
My work in granular mechanics has been primarily at the scale of particle pairs
clusters. I am mainly interested in the discrete mechanics of granular materials
and have use the Discrete Element Method to simulate granular deformation
and to explore and visualize the micro-scale behaviors that develop during
deformation. I have investigated behaviors such as shear band formation,
stress-induced anisotropy, strain-gradient and non-local material dependence,
softening, and dilation—all from a micro-mechanical viewpoint that can be
verified through simulation.
After over one hundred years since the pioneering work of Osborne Reynolds,
it seems that the promise of micro-geomechanics is still largely unfulfilled.
Many pervasive phenomena have not yet been explained through micro-
mechanical analyses, and these phenomena have instead been studied with
continuum models that presume a particular constitutive behavior. Micro-
mechanical measures are only now being advanced for notions that have long
been evoked in the language of soil mechanics: notions such as interlocking,
disturbance, particle rotations, particle rolling, mineral skeleton, internal
instability, and creep. Although this assessment is somewhat pessimistic, it is
balanced by the recent success of others at estimating the small-strain modulus
from the contact stiffness as well as the dependence of the modulus on the
confining stress and other factors. However, many behaviors have not yet
been explained with micro-mechanical analyses, including the following:
1. The observed effects of inter-particle friction and confining stress on the
peak strength, residual strength, and dilation rate.
2. The onset and evolution of shear bands. Experiments by the Grenoble
group have shown that the thickness and orientation of shear bands
depend on the particle size and confining stress, and these observations
require a consistent explanation.
3. The softening rate that is observed beyond the peak state, and its
dependence on the confining stress, the coefficient of inter-particle
friction, the confining stress, and the initial density.
4. The observed dependence of granular stiffness on the gradients of strain.
Numerical simulations have been able to reproduce many of these behaviors,
and simulations have provided useful predictive information about constitutive

ehavior under conditions that would otherwise be difficult to create in a
physical laboratory. Simulations have not yet been fully exploited for
extracting consistent micro-scale rationales for macro-scale behavior.
The unresolved behaviors that were listed above are associated with
moderate-to-large strains. At such strains, particle rotations are large and
granular motions deviate greatly from the motions of a uniform deformation
field. I have concluded that, under these conditions, the only reasonable
means of characterizing the particle motions is by constructing general
expressions for the discrete matrix stiffness of particle clusters or assemblies.
With this approach, granular stiffness can be shown to originate from the
contact stiffnesses (a mechanical form of stiffness) and from the particle
shapes at their contacts (a geometric form of stiffness). Although the
geometric terms are negligible at small strains, they become significant during
failure and flow due to the dominance of particle rotations and rolling. This
stiffness-based approach affords the ability to investigate internal bifurcation
modes of the particle motions and enables characterizing the internal stability
of granular materials at the scale of particle clusters. When combined with
DEM simulations, the method can also be used to quantify and visualize the
evolution of material hardening, softening, and instability. Although the work
is in its formative stage, I view this micro-mechanics approach as a means of
systematically resolving the four unresolved behaviors that were listed above.

Colorado School of Mines
My interest on micro-mechanics of soil stems from my scientific curiosity and
the motivation on how to effectively describe state of stress and water
movement in unsaturated soils. The path to reaching this goal is to accomplish
the objectives of: (1) clarifying physical mechanisms for soil water retention at
intermolecular and particle scales, (2) clarifying physical mechanisms for
interparticle forces, particularly under partially saturated condition, (3)
developing useful simulation and experimental tools to qualify the magnitude
of water potentials and interparticle forces, and (4) developing the up scaling
theory to define stress, strain and stress-strain laws that are based on
intermolecular and inter-particle forces. Ultimately, these objectives will lead
to better define state of stress and water movement in unsaturated soils
encountered in daily geotechnical and environmental engineering problems.
In the past two decades I have been using theoretical, numerical, and,
experimental tools toward the above goal and objectives. I have established a
framework to calculate electric double layer repulsion between inclined clay
particles [1]. Using the continuum mechanics based FEM, empirical and
practical formulas are developed to calculate the magnitude of both electric
double layer repulsion and induced moment among inclined clay particles [1]. A
DEM framework is also developed to simulate physico-chemical and
mechanical interaction among clay particles [2-3]. Recent activities have been
focusing on quantifying interparticle capillary force by employing
thermodynamic free energy approach [4], and verifying the characteristics of
capillary force by employing microscopic experiments for particles at 100 μm
scale [5]. The free energy approach also provides a rigorous basis for obtaining
the so-called “soil-water characteristic curve” for particles from submicron to
mm scales [6]. This approach completely eliminates empirical and
phenomenological parameters that traditional macroscopic models are based
on. The fundamental understanding of interparticle forces at the
intermolecular and particle levels also leads to the postulate of suction stress
characteristic curve (SSCC) concept [7], which is a generalization the classical
effective stress concept proposed by Bishop (1957). The SSCC concept has been
validated experimentally by the macroscopic shear strength data found in the
literature [7]. The SSCC also is demonstrated to be practical and useful in
analyzing many geotechnical problems such as bearing capacity, earth pressure
[8], and slope stability analysis [9].

1. Lu, N., Numerical Study of the Electrical Double-Layer Repulsion between
Non-parallel Clay Particles of Finite Length, Ph.D. Dissertation, Johns
Hopkins University, Baltimore, MD, 1991.
2. Anandarajah, A. and Lu, N., Structural analysis by the distinct element
method, Journal of Engineering Mechanics, ASCE, 117, 2156-2163, 1991.
3. Anderson, M.T, and Lu, N., The role of microscopic physico-chemical forces
in large volumetric strains for clay sediments, Journal of Engineering
Mechanics, ASCE, 127(7), 710-719, 2001.
4. Lechman, J., and Lu, N., Capillary stress and water retention between two
uneven-sized particles, submitted to Geotechnique.
5. Lechman, J., and Lu, N., Experimental verification of capillary force and
water retention between two uneven-sized particles, submitted to
Geotechnique.
6. Lechman, J., and Lu, N., Hysteresis of soil suction and capillary stress in
mono-disperse disk-shaped particles, in press Journal of Engineering
Mechanics.
7. Lu, N., and Likos, W.J., Unsaturated Soil Mechanics, John Wiley and Sons,
556 pp., 2004.
8. Lu, N., and Griffiths, D.V., Profiles of steady-state suction stress in
unsaturated soils, Journal of Geotechnical and Geoenvironmental
Engineering, 130(10), 1063-1076, 2004.
9. Griffiths, D.V., and Lu, N., Unsaturated slope stability analysis with steady
infiltration or evaporation using elasto-plastic finite elements,
International Journal of Numerical and Analytical Methods for
Geomechanics, 29, 249-267, 2005.

Reader in Geomechanics
Nottingham Centre for Geomechanics
University of Nottingham, UK
http://www.nottingham.ac.uk/%7Eevzgrm/evzgrm.html
� Micro mechanical origins of yield, compressibility
� Constitutive modelling of granular materials
� Mechanics of railway ballast behaviour
� Discrete element modelling of granular materials, including ballast and
asphalt
� Geogrid-reinforced ballast
Presentations: Micro mechanics of Railway Ballast Behaviour
These presentations will examine the development of a simple box test for
simulating train loading and tamping on railway ballast. The research
investigates the trackbed stiffness, accumulation of permanent settlement and
associated degradation for a number of ballasts and examines how the results
correlate with a number of proposed simple index tests. It appears at first that
dynamic tests involving a revolving drum are the best indicators of ballast
performance. However, if particle shape and strength are both accounted for
in a new lumped parameter, this new parameter too correlates with
degradation in the box tests. The study also examines the performance of
ballast mixtures in the box tests. It appears that up to 30% of poor quality
ballast (which does not meet the current Specification) can be included in the
aggregate without affecting performance too much, so that the current
Specification is still met. Higher quantities of poor quality ballast can be
included however, if these are placed in the lower (untamped) layer. Finally,
the new Nottingham Railway Test Facility is described. This new facility has
been recently commissioned and has generated the first data, which are briefly
presented here.
1. McDowell, G.R., Lim, W.L. and Collop, A.C. (2003) Measuring the strength
of railway ballast. Ground Engineering 36, No. 1, 25-28.

2. McDowell, G.R., Lim, W.L., Collop, A.C., Armitage, R. and Thom, N.H. (2004)
Comparison of ballast index tests with performance under simulated train
loading and tamping. Proc. ICE – Geotechnical Engineering 157, No. GE3,
151-161.
3. McDowell, G.R., Buchanan, J. and Lim, W.L. (2004) Performance of ballast
mixtures. Ground Engineering 37, No. 10, 28-31.
4. Lim, W.L., McDowell, G.R. and Collop, A.C. (2005) The application of
Weibull statistics to the strength of railway ballast. Granular Matter 6, No.
4, 229-237.
5. Lim, W.L. and McDowell, G.R. (2005) Discrete element modelling of railway
ballast. Granular matter 7, No. 1, 19-29.
6. McDowell, G.R., Lim, W.L., Collop, A.C., Armitage, R., Thom, N.H. (2005)
Laboratory simulation of the effects of train loading and tamping on ballast
performance. Proc. ICE – Transport 158, No. TR1, in press.
7. Lim, W.L., McDowell, G.R. and Collop, A.C. (2005) Quantifying the relative
strengths of railway ballasts. Proc. ICE – Geotechnical Engineering 158, No.
GE2, in press.

University Distinguished Professor, Emeritus
Virginia Tech, Blacksburg, VA 24061-0105, U.S.A.
Email: jkm@vt,edu
The overriding objective of my research and study in Geotechnics for more
than 50 years has been the development of an understanding of the factors
that determine and control the engineering properties and behavior of soils
under different conditions. The emphasis is on what they are, why they are
what they are, and how they act. To meet this objective it is necessary to
examine the composition of soils in terms of their particulate and pore fluid
compositions and the interactions of these phases with each other and the
surrounding environment.
Trends and developments in geoengineering problems and projects have now
moved well beyond the "classical" realm of soil mechanics and foundation
engineering wherein engineering mechanics based approaches by themselves
were generally adequate for obtaining reasonable results. Environmental
problems require major geotechnical inputs (Environmental Geotechnics).
Natural hazards and disasters, risk assessment and mitigation applied to
existing structures and earthworks, soil stabilization, ground improvement, and
soil as a construction material, and the development of new computational,
geophysical, and sensing methods all require looking at soil behavior in new
ways. More and more it is becoming appreciated that geochemical and
microbiological phenomena and processes play an essential role in many types
of geotechnical problems.
We seem to be at a point now where we are able to develop reasonably good
descriptions, and even quantifications, of the compositions, fabrics and
structures of many soils at the micro scale. Similarly, we seem able to describe
macro-scale behavior on a phenomenological basis with constitutive models of
varying levels of empiricism and complexity. Although the micro scale
knowledge is many times helpful in shaping and refining the macro scale
models, there remains a big gap in direct quantification of macro scale behavior
in terms of first principles of micro behavior. It is to be hoped that this
workshop will serve as a milestone in bridging this gap.
1. Fundamentals of Soil Behavior, 2nd edition, Wiley, 1993, 437 pp. (Third
Edition, by J. K. Mitchell and K. Soga, Wiley, May 2005)

2. "Practical Problems from Surprising Soil Behavior," 20th Terzaghi Lecture,
Journal, Geotechnical Engineering Division, ASCE, Vol. 112, No. 3, March
1986, pp. 255-289.
3. "Conduction Phenomena: From Theory to Geotechnical Practice,"
Geotechnique, 41, No. 3, 1991, pp. 299-340.
4. "Time - The Fourth Dimension of Soil Behavior in Geotechnical
Engineering," The Seventeenth Nabor Carrillo Lecture, Mexican Society of
Soil Mechanics, Guadalajara, Mexico, 2004.

Montana State University
Nondestructive Measurements of Soil Geotechnical Properties Using X-Ray
Computed Tomography
The mechanical behavior of granular soils is highly dependent on the particle
microstructure. The microstructure is commonly referred to as the soil fabric,
which includes the shape, distribution, and arrangement of particles and void
space. Because of the inherent difficulties in measuring soil properties on a
microscale, geotechnical engineers use macro properties to estimate, or
predict, the response of soil when subjected to changes in the state of stress.
These macro properties (void ratio, porosity, density, uniformity, etc.) are used
to represent gross or average measures of the soil microstructure in terms of
engineering behavior; i.e., strength, compressibility, and permeability.
Engineers generally recognize the important influence of microstructure on the
geotechnical behavior of soils; however, until recently, observation and
quantification of soil microstructure has been a tedious, time consuming, and
destructive process.
At Montana State University we have been working on developing systematic
nondestructive approaches for quantifying microscale measurements of local
void ratio distribution, gradation, pore size distribution, and relative density of
scanned digital images. Results of this research are anticipated to include an
established procedure for conducting X-ray computer-aided tomography (CT)
scanning on natural and processed soils. A rational systematic approach is
under development to quantify two-dimensional and three-dimensional digital
images, and to relate the quantified microscale measurements to traditional
macroscale geotechnical measurements.
Soil Frost Action
Montana State University has a well-established research center for studying
snow and ice mechanics, including avalanche forecasting and microstructural
behavior of snow and ice particulates. By combining the resources of our cold
regions center with our micro-geomechanics research, we hope to ultimately
develop a better understanding of the microstructure interactions that occur
when soil is exposed to freezing and thawing temperatures by scanning soils in
a controlled environmental chamber where the effects of pore fluid,
temperature, and soil structure can be observed and quantified.

Three-Dimensional Analyses
Most of our work to date with the CT scanning equipment has focused on the
development of image processing techniques to estimate soil properties from
two-dimensional x-ray images. We recently started working with three-
dimensional scans, which will be used to validate hypotheses regarding particle
interactions and to develop approaches for examining how soil fabric may
influence hydraulic conductivity, pore structure, pore connectivity, and
tortuosity. Future work using the CT scanning equipment will involve the
examination of soil microstructure behavior during the shearing process. Since
CT scanning is non-destructive, the same soil sample could be measured at
various stages in the shearing process to determine the effects of particle
shape, alignment, and interaction during shear.

Department of Civil Engineering
University of Bristol, UK
My research has spanned the continuum from laboratory testing, through
development of constitutive models for soils, to analysis of soil:structure
interaction and response of geotechnical systems. I have developed a hierarchy
of soil models which can be clearly linked with physical observations of modes
of soil response and which can be accessible to practising engineers. The
modelling is informed by experimental observation.
Conventional testing of geotechnical materials concentrates on axial symmetry
–confined one-dimensional loading. I have sought to extend the range of
exploration of stress and strain space using devices which permit independent
variation and control of all three principal stresses and which permit controlled
rotation of principal axes. Thus I have been testing with a true triaxial
apparatus since 1970, conducted a series of research projects with the simple
shear apparatus and now in Bristol have a unique group of apparatus: rigid
boundary true triaxial, flexible boundary cubical cell (Boulder design), and
torsional hollow cylinder apparatus (Imperial College design).
Soil:structure interaction is controlled by stiffness properties. Constitutive
modelling has recognised the need to describe using plasticity models regions
of response that were classically regarded as elastic particularly for stress paths
which involve non-monotonic loading, of which the paths followed by soil
elements subjected to seismic or cyclic loading provide an obvious example.
This modelling has been assisted by developments in laboratory
instrumentation: higher resolution of deformation measurement allows small-
strain nonlinearities to be reliably detected (at shear strain levels below
0.001%); laboratory geophysics using piezoceramic ‘bender’ elements is
proving particularly useful in assessing evolution of stiffness anisotropy from
measurements of shear wave velocities.
1. Muir Wood, D (1998) Life cycles of granular materials. Phil. Trans. Roy. Soc.
London A356:1747:2453-2470
2. Gajo, A and Muir Wood, D (1999) A kinematic hardening constitutive
model for sands: the multiaxial formulation. International Journal for
Numerical and Analytical Methods in Geomechanics 23 925-965.

3. Muir Wood, D and Kumar, GV (2000) Experimental observations of
behaviour of heterogeneous soils. Mechanics of Cohesive-Frictional
Materials 5 5,373-398.
4. Muir Wood, D (2002) Some observations of volumetric instabilities in soils.
IUTAM Symposium on Material instabilities and the effect of
microstructure, Austin, Texas: May 2001 International Journal of Solids and
Structures 39 13-14, 3429-3449
5. Muir Wood, D (2004) Experimental inspiration for kinematic hardening soil
models. Journal of Engineering Mechanics, ASCE 130 6, 656-664
6. Gajo, A, Bigoni, D & Muir Wood, D (2004) Multiple shear band
development and related instabilities in granular materials. Journal of the
Mechanics and Physics of Solids 52 2683-2724.

Yamaguchi University
Grain damage in Sand During Compression
Even for the same material the yielding characteristics are dependent on the
grading curve with much more marked yielding occurring for uniformly graded
sands in comparison with well graded sands. This is related to the nature of the
microscopic particle crushing during yielding. As the material becomes well
graded sand, the nature of the particle crushing change from the sudden
catastrophic onset of splitting to the gradual splitting of smaller size particle,
breaking of the smaller asperities and grinding of the surface. It is important to
know the grain damage in sand during compression as well as grain movement.
In the presentation, the visualisation of uniformly graded sand during
compression will be given. The tests were conducted for small specimen to
mount on a X-ray CT system.
1. Nakata, Y., Hyde, A.F.L., Hyodo, M. and Murata, H., (1999) "A probabilistic
approach to sand crushing in the triaxial test," Geotechnique, Vol.49, No.5,
pp.567-583.
2. Nakata, Y., Hyodo, M., Hyde, A.F.L., Kato, Y. and Murata, H., (2001)
"Microscopic particle crushing of sand subjected to high pressure one-
dimensional compression" Soils and Foundations, Vol.41, No.1, pp.69-82.

Department of Civil Engineering
University of New Mexico
Albuquerque, NM 87131
tang@unm.edu | http://geolab.unm.edu
Dr. Ng research interests are in micromechanics of particulate media and
computational mechanics. He has been using discrete element method (DEM)
to model assemblies of granular materials for 20 years. Understanding the
behavior of granular materials from a micromechanical point of view is the
ultimate goal. Effort has been spent to improve the numerical tool (DEM) in
the past. Current endeavor focuses on the discovery of micromechanical
parameters that relate to macroscopic behavior.
Sample preparation
Failure envelope (numerical simulation)

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2
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Micro-parameters
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Linkage between micro- and macro- parameters
1. Ng, T.-T. (2004). “Shear Strength of Assemblies of Ellipsoidal Particles.”
Geotechnique, 54(10), 659-669.
2. Ng, T.-T. (2004). “Macro-and Micro-Behaviors of Granular Materials under
different Sample Preparation Methods and Stress Paths.” International
Journal of Solids and Structures, 41(21), 5871-5884.
3. Ng, T.-T. (2004). “Behaviors of Ellipsoids of Two-size,” Journal of
Geotechnical and Geoenvironmental Engineering, ASCE, 130(10), 1077-
1083.

Dept. Civil and Environmental Engineering
Imperial College London
Coupling DEM simulations with laboratory tests for validation.
In this series of studies DEM simulations have been coupled with carefully
designed physical tests. The macro-scale response of the DEM simulations has
compared with the macro-scale response observed in the physical tests. These
studies have quantitatively demonstrated the accuracy of DEM models to
capture the material response observed in standard soil mechanics tests. Once
validated, the DEM model has been used to develop an appreciation of
particle-scale interactions underlying the material response. The laboratory
tests considered have included both two-dimensional and three-dimensional
model soils.
Homogenization.
DEM analyses produce results in terms of the discrete parameters of particle
displacements and contact forces. It is necessary to “translate” these results
into the continuum parameters of stress and strain so that the results of DEM
analyses can be related to the broader base of knowledge in soil mechanics.
Many researchers have used relatively simple linear triangulation-based
interpolation approaches. A non-linear approach was developed and has been
applied to interpret the results of some three-dimensional and two
dimensional simulations.
Influence of particle geometry on granular material response.
Many of the three dimensional DEM analyses of particulate materials to date
have considered smooth convex particles, i.e. spheres and ellipsoids. The
response of these idealized materials is qualitatively very similar to soil
response and these studies have provided us with important insights into the
response of granular materials. However, if DEM analyses are to be used for
quantitative predictions of soil response it is important to establish to what
degree the non-convex shape of real particles influences their response. The
image analysis techniques proposed by Bowman et al (2001) are useful to
quantitatively determine the “quality” of the idealised particles. Sphere cluster
particles are being developed and validated to facilitate this study.

PhD student, Department of Chemical Engineering
University of Cambridge, New Museums Site
Pembroke Street, Cambridge, CB2 3RA, UK
E-mail: mjcp2@cam.ac.uk
http://www.cheng.cam.ac.uk/research/groups/paste/current/mjcp.html
Highly concentrated particulate solid-liquid suspensions, or particulate pastes,
are employed in many industrial sectors to allow manufacture of shaped
products. Common manufacturing routes feature operations such as extrusion
and injection moulding, in which pastes undergo large strains in order to take
on the desired shape.
Many flaws may develop within the paste during processing. One such flaw is
liquid phase migration, where liquid pressure gradients build in the pores
between the particles in the paste. Such pressure gradients drive flow of the
liquid phase relative to the solids skeleton and cause inhomogeneities in the
distribution of liquid within the paste during processing. When severe, this lack
of homogeneity can render the paste product useless.
Our goal is further understanding of the mechanisms underlying this problem,
via the use of finite element modelling. Deformation of pastes within two
common experimental geometries, namely ram extrusion and squeeze flow,
has been simulated within the ABAQUS/Standard code. These geometries are
routinely used to characterisation the flow behaviour of pastes. The paste is
modelled as a soil using the modified CamClay constitutive law, with pore liquid
flow simulated using Darcy’s Law. The use of this soil mechanics model allows
representation of behaviour such as dilation of the paste during shearing of the
material. Predictions from this model are to be verified by experiment.
A potential solution to the problem exists due to the fact that pastes are
formulated products, i.e. both the particulate solid ingredients and the liquid
may be altered to give rise to different product properties or processing
behaviour. The goal of this modelling technique, once verified, is to
understand how the formulation of the paste affects its resistance to the
problem of liquid phase migration, and to develop a basic criterion for the
design of pastes such that this problem can be avoided at the design stage.

Department of Civil Engineering
Kansas State University
Manhattan, KS 66506, U.S.A
peric@ksu.edu
� Strain localization in general and in particular with emphasis on clays
whereby the strains are concentrated into extremely narrow zones.
� Fundamental physics and chemistry of micro- and nano- scale processes
that control dissipation of energy associated with strain localization and
thus the macroscopic failure.
� Development of physically based numerical models for capturing the strain
.
localization in clays by bridging the gap between macro- and nano- scales.
Numerical modeling by FEM
(PSE-local displacements)
Physical modeling in biaxial apparatus
(PSC-local displacements)

1. Ottosen, N.S., Runesson, K., and Perid, D. “Discontinuous Bifurcations of
Elastic-Plastic Solids at Plane Stress and Plane Strain”, Int. J. Plasticity, Vol.
7, No. ½, 1991, pp. 99-121; cited 63 times.
2. Perid, D., Runesson, K., and Sture, S. “Evaluation of Plastic Bifurcation
Results for Plane Strain versus Axisymmetry”, J. of Engineering Mechanics,
ASCE, Vol. 118, No. 3, 1992, pp. 512-524; cited 20 times.
3. Runesson, K., Perić, D., and Sture, S. “Influence of Pore Fluid
Compressibility on Localization in Elastic-Plastic Porous Solids”, Int. J.
Solids and Structures, Vol. 33, No. 10, 1996, pp. 1501-1518; cited 22 times.
4. Perid, D., and Ayari, M. A. “On the analytical solutions for the three-
invariant Cam clay model”, Int. J. Plasticity, Vol. 18, No. 8, 2002, pp. 1061-
1082; cited 8 times.
5. Perid, D. and Hwang, C. “Experimental investigation of plane strain
behavior of Georgia kaolin”, Proc. of Eighth Int. Symposium on Numerical
Models in Geomechanics, April 10-12, 2002, Rome, eds. Pande, G.N. and
Pietruszczak, S., Balkema, 2002, pp. 93-98.

Assistant Professor, Civil and Environmental Engineering
Univ. of Southern California, Los Angeles, CA 90089-2531
arechenm@usc.edu
The geotechnical engineering profession has grown complacent with prediction
to “order of magnitude” accuracy, attributing uncertainties to the
capriciousness of “mother nature” or an inability to sense the full extent of
material heterogeneity at the field scale. Arguably, the human body, within its
own relative scale, also comprises variability and uncertainty, and is equally
opaque, yet research initiatives in the health sciences are aimed at developing
understanding to the nano-scale, “genome”-scale, and beyond. Given the
societal value of safe and reliable geotechnical structures, it is timely that
equivalent research efforts in geotechnics aim for a similar course of
development.
The ability to correctly quantify and interpret elemental soil response forms a
first, crucial step toward extrapolating predictability to field-scale problems.
The mechanistic characterization of soils in the form of constitutive models
involves the encapsulation of controlled experimental measurements into a
form conducive to extrapolation beyond the specific conditions that existed
during calibration. Generally, soil constitutive models are calibrated from
boundary measurements on “homogeneous” laboratory specimens;
characterization, then, is relegated to an averaged homogenized material. Our
recent research, employing local, digital imaging-based deformation
measurement techniques, has verified that laboratory specimen deformations
can be locally nonuniform (Figure 1) as a direct consequence of material
nonuniformity. A probabilistic approach to model calibration is being pursued
which considers the effects of heterogeneity and inter-specimen variability on
model performance and holds promise for developing more robust predictive
tools.
Figure 1. x-, y-, and z-direction displacements of a sand specimen during preliminary
stages of triaxial compression

Traditional, theoretical solutions to the bifurcation problem assume that the
deformation gradient across a shear band, once it has formed, is uniform.
Imaging-based, particle-scale displacement measurements within shear bands
in sand specimens undergoing plane strain loading have revealed that the
displacement field within a fully-formed shear band is characterized by
periodically alternating regions of high shear and high rotation along the shear
band length. Similar measurements are also providing insight as to the
deformation mechanisms which accompany the formation of shear bands, as
well as factors that contribute to the formation of single or multiple band
structures. Micro-scale measurements such as these are proving essential
toward improved scientific understanding of bifurcation phenomena in
particulate materials.

School of Civil and Environmental Engineering
Georgia Institute of Technology
� Fundamental study of particulate materials and phenomena
(Prior work on: diagenetic processes, fabric control and modification,
energy coupling, environmental effects, fines migration, mixed fluids,
multi-scale interaction, and hydrates formation).
� Distinct laboratory devices and experimental procedures
(Prior work on: micro-scale experimentation, elastic and electromagnetic
waves, advanced signal processing and inversion problem solving
techniques, tomographic imaging, passive and active systems).
� Macro-measurements are interpreted at the particle-level
(Prior work on: micromechanical models in coarse materials, molecular
scale analyses in clays).
� Applications
(Prior work on: geotechnical characterization, process-monitoring including
tomographic techniques, earthquake engineering, resource recovery -
mining, petroleum and methane hydrates).

Department of Civil, Construction and Environmental Engineering
482 Town Engineering Building
Iowa State University, Ames, Iowa 50011-3232, USA
Phone: 515 294 3988; Fax: 515 294 8216
Email: rsharma@iastate.edu
� Ph.D. (Geotechnical Engineering – Unsaturated Soils): University of Oxford,
England, 1998.
� M.S. and D.I.C. (Soil Mechanics and Environmental Geotechnics): Imperial
College of Science, Technology & Medicine, London, 1994.
� M.Tech. (equivalent to M.S.) [Rock Mechanics]: Indian Institute of
Technology (IIT), Delhi, 1984.
� B.S. (Civil Engineering): Z. H. College of Engineering and Technology, AMU,
Aligarh, India, 1983. First class with honors.
Seven years as a faculty member in geotechnical and geoenvironmental
engineering and nine years in industry
I have developed my research into a number of directions and some of my
research activities and interests are:
� Unsaturated/saturated soil mechanics: fundamental studies and field
applications in design and analysis of geoinfrastructure.
� Geotechnical earthquake engineering, especially aimed at the
geoinfrastructure analysis and design involving unsaturated soils.
� Characterization and constitutive modeling of soils, rocks, and
geomaterials.
� Laboratory, in situ, and field instrumentation and testing of soils, rocks,
and pavement materials.
� Ground improvement techniques including geogrid reinforced granular
piles, granular pile-anchors and geopile anchors.
� Use of innovative techniques including geophysical testing such as Ground
Penetrating radar GPR, image analysis technique IAT, and scanning
electron microscopy SEM.

� Geoenvironmental engineering involving containment systems such landfill
liners, covers, and vertical barriers. Fate and transport of contaminants in
saturated and unsaturated soils.
� Application of numerical techniques in Geotechnical and
Geoenvironmental Engineering.
1. Sharma, R.S. and Phanikumar B.R. (2005) "A laboratory study of heave
behavior of expansive clay reinforced with geopiles". Journal of
Geotechnical and Geoenvironmental Engineering, ASCE, (in press).
2. Phanikumar B.R. and Sharma, R.S. (2005) "Volume change behavior of fly
ash- stabilized clays.” Journal of Materials in Civil Engineering, ASCE,
(Accepted for publication).
3. Phanikumar B.R., Sharma R. S., Rao A.S. and Madhav M.R. (2004).
“Granular pile-anchor foundation (GPAF) system for improving the
engineering behavior of expansive clay beds”. Geotechnical Testing
Journal, ASTM. Vol. 27, No3, p. 279-287.
4. Sharma R. S., Phanikumar B.R. and Nagendra (2004). “Compressive load
response of
5. geogrid-reinforced granular piles in soft clays”. Canadian Geotechnical
Journal, Vol. 41, p. 187-192.
6. Phanikumar B.R., Sharma R. S. (2004). “Effect of fly ash on engineering
properties of expansive soils”. Journal of Geotechnical and
Geoenvironmental Engineering, ASCE, Vol. 130, No.7, p. 764-767.
7. Rao, A.S., Phanikumar B.R., and Sharma, R.S. (2004). “Prediction of
swelling characteristics of remoulded and compacted expansive soils using
free swell index”. The Quarterly Journal of Engineering Geology and
Hydrogeology, Vol. 37, No. 3, p. 217-226.
8. Wheeler S.J., Sharma R.S. and Bussien M.S.R. (2003). “Coupling hydraulic
hysteresis and stress-strain behavior in unsaturated soils”. Géotechnique
Vol 53, No1, p. 41-54.
9. Sharma R. S., Mohamed M.H.A. (2003). “Patterns and mechanisms of
migration of light nonaqueous phase liquid in an unsaturated sand”.
Géotechnique,Vol. 53, No.2, p. 225-239.
10. Gallipoli D., Gens A., Sharma R.S. and Vaunat J. (2003). “An elasto-plastic
model for unsaturated soil incorporating the effect of suction and degree
of saturation on mechanical behavior”. Géotechnique, Vol. 53, No.1, p.
123-135.

11. Sharma R. S., Mohamed M.H.A. (2003). “An experimental investigation of
LNAPL migration in an unsaturated/saturated sand”. Journal of
Engineering Geology Vol. 70/3-4, p.305-313.
12. Sharma R.S. and Al-Busaidi T.S (2001). “Groundwater pollution due to a
tailings dam”. Journal of Engineering Geology, Vol. 60/1-4, p.235-244.
13. Houlsby G.T. and Sharma R.S. (1999). “A conceptual model for the yielding
and consolidation of clays”. Géotechnique, Vol. 49, No.4, p. 491-501.
� Serving on the Editorial Board, Journal of Geotechnical and
Geoenvironmental Engineering ASCE.
� Serving on the Editorial Board, International Journal of Geotechnical and
Geological Engineering.
� Member, Technical Committee TC6 (Unsaturated Soils), International
Society for Soil Mechanics and Geotechnical Engineering.
� Technical Committee member for the International Conference on
Unsaturated Soils UNSAT 2006, Phoenix, Arizona.

Associate Professor, Civil Engineering
Rowan University
201 Mullica Hill Rd., Glassboro, NJ-08028, USA.
E-mail: sukumaran@rowan.edu
Phone: (001)-856-256-5324; Fax: (001)-856-256-5242
1. Quantification of particle morphology in 2-d and 3-d (Sukumaran &
Ashmawy, 2001; Corriveau et al., 2004) [Web page of interest:
http://users.rowan.edu/~shreek/share/nsf-cms-3D/]
2. Relationship between particle morphology and shear strength (Sukumaran
& Ashmawy, 2001)
3. Influence of particle morphology on hopper flow rate (Sukumaran &
Ashmawy, 2003)
4. Discrete element modeling of angular particles (Ashmawy et al., 2003)
5. Particle reconstruction and 3-d discrete element modeling of soils: This is
an ongoing study. The study focuses on the development of automated
image processing algorithms that can estimate 3-D shape-descriptors for
particle aggregates using a statistical combination of 2-D shape-descriptors
from multiple 2-D projections. This will eventually be used in a 3-d discrete
element modeling program.

1. Sukumaran, and Ashmawy, A. (2001), "Quantitative Characterization of
Discrete Particles," Geotechnique, Vol. 51, No. 7, pp. 619-627.
2. Jonathan, Corriveau, Shreekanth Mandayam, and Beena Sukumaran,
(2005), “ 3-D Shape descriptors for geomaterial aggregates using multiple
projective representations,” ASCE Geofrontiers conference, Austin, TX.
3. Sukumaran, B., and Ashmawy, A.K. (2001), “Influence of Inherent Particle
Characteristics on the Strength Properties of Particulate Materials,” Annual
International Society of Offshore and Polar Engineering Conference, Oslo,
Norway.
4. Sukumaran, B., and Ashmawy, A.K. (2003), “Influence of inherent particle
characteristics on hopper flow rate,” Powder Technology, Vol 138, pp 46-
50.
5. Alaa K. Ashmawy, Beena Sukumaran, Vinh Hoang (2003), “Evaluating the
Influence of Particle Shape on Liquefaction Behavior Using Discrete
Element Modeling,” Annual International Society of Offshore and Polar
Engineering Conference, Honolulu, Hawaii.

School of Engineering
University of Birmingham
Edgbaston
Birmingham B15 2TT, UK
Email – c.thornton@bham.ac.uk
I do not have an obsessive interest in geomechanics although that is the area
from which I evolved. I consider myself to be interdisciplinary but focussed on
my obsession with particle systems be that in the context of geomechanics,
particle technology, theoretical physics or general engineering mechanics – I
don’t care. My research group have been active in DEM simulations of particle
systems since 1980 and during the last twenty five years we have been willing
to examine any problems – given the appropriate level of funding. Currently,
we have three EPSRC funded projects – (i) a geomechanics project in which we
are examining the 3D elastic response of granular material, the detailed
micromechanics of plane strain deformation and general ‘stress probing’ in 3D
stress space; (ii) a particle technology project in which we are simulating gas-
fluidised beds in order to examine the effect of surface energy on the bubbling
and turbulent behaviour of beds composed of

Professor of Civil Engineering
Université Joseph Fourier, Grenoble
(Laboratoire Sols, Solides, Structures)
� Graduated in Civil Engineering in 1988 at the University of Napoli Federico
II (Italy).
� Obtained a Ph.D. in Geotechnical Engineering in 1994 at the University of
Roma "La Sapienza" (Italy) presenting a dissertation on "Strain Localization
and Rupture Processes in Stiff Overconsolidated Clays".
� Post-Doctoral Research Fellow at the Department of Civil Engineering of
Northwestern University, Evanston, IL (USA), March 1994 through
September 1995. Projects included experimental and numerical
investigation on undrained instability of sand (liquefaction).
� Post-Doctoral Research Fellow at Laboratoire 3S of Université J. Fourier,
Grenoble (France), November 1995 through October 1997. Projects
included experimental and numerical investigation on instability of stiff
marls.
Experiments on strain localization in saturated sand, clay, and rock; Crack
propagation in rocks; Constitutive behavior of rocks and soils, including post-
peak response; Liquefaction of sand; Measurement of pore water pressure in
the laboratory; Stereophotogrammetry and Digital Images Correlation;
Experimental and Numerical micro mechanics; Incrementally non-linear
constitutive models, including hypoplasticity. Numerical methods, including
Finite Elements and Boundary Elements; Soil-structure interaction; Excavations
and tunnels; Analysis and improvement of slope stability
1. Finno R.J., Harris W.W, Mooney M.A., Viggiani G. (1997) - Shear Bands in
Plane Strain Compression of Loose Sand. Géotechnique, Vol. 47, No. 1, 149-
165.
2. Mooney M.A., Viggiani G., Finno R.J. (1997) - Undrained Shear Band
Deformation in Granular Media. Journal of Engineering Mechanics, ASCE,
Vol. 123, No. 6, 577-585.

3. Tamagnini C., Viggiani G., Chambon R., Desrues J. (2000) – Evaluation of
different strategies for the integration of hypoplastic constitutive
equations. Application to the CLoE model. Mechanics of Cohesive-Frictional
Materials, Vol. 5, No. 4, 263-289.
4. Tamagnini C., Viggiani G., Chambon R. (2000) - A review of two different
approaches to hypoplasticity. In: Constitutive Modelling of Granular
Materials, D. Kolymbas editor, Balkema, D. Kolymbas editor, Springer, 107-
145.
5. Viggiani G., Tamagnini C. (2000) – Ground movements around excavations
in granular soils: a few remarks on the influence of the constitutive
assumptions on FE predictions. Mechanics of Cohesive-Frictional Materials,
Vol. 5, No. 5, 399-423.
6. Viggiani G., Küntz M., Desrues J. (2001) - An experimental investigation of
the relationship between grain size distribution and shear banding in
granular materials. In: Continuous and Discontinuous Modelling of
Cohesive Frictional Materials, P.A. Vermeer et al. Eds. (Lecture Notes in
Physics, Vol. 568), Springer, 111-127.
7. Tamagnini C., Viggiani G. (2002a) - On the incremental non-linearity of
soils. Part I: theoretical aspects. Rivista Italiana di Geotecnica, No. 1/02, 44-
61.
8. Bilotta E., Flora A., Lanier J., Viggiani G. (2002) - Experimental observation
of the behaviour of a 2D granular material with inclusions, Rivista Italiana
di Geotecnica, No. 3/02, 9-22.
9. Calvetti F., Viggiani G., Tamagnini C. (2003) - A numerical investigation of
the incremental non-linearity of granular soils. Rivista Italiana di
Geotecnica (Special Issue on Mechanics and Physics of Granular Materials),
No. 3/03, 11-29.
10. Calvetti F., Viggiani G., Tamagnini C. (2003) - Micromechanical inspection
of constitutive modelling. Proceedings of the International Symposium on
Constitutive Modelling and Analysis of Boundary Value Problems, Napoli,
Hevelius, 187-216.
11. Desrues J., Viggiani G. (2004) - Strain localization in sand: an overview of
the experimental results obtained in Grenoble using
stereophotogrammetry, International Journal for Numerical and Analytical
Methods in Geomechanics, Vol. 28, No. 4, 279 –321.
12. Chambon R., Caillerie D., Viggiani G. (2004) - Loss of uniqueness and
bifurcation vs. instability: some remarks. Revue Française de Génie Civil,
Vol. 8, No. 5-6 (Special Issue on Failure, Degradation and Instabilities in
Geomaterials), 517-535.

13. Viggiani G., Calvetti F., Tamagnini C. (2004) - Micro mechanics of the
incremental response of virgin and preloaded granular soils to deviatoric
stress probing. In: CDM2004, Continuous and Discontinuous Modelling of
Cohesive Frictional Materials, P.A. Vermeer et al. Eds., Balkema, 121-133.
14. Viggiani G., Lenoir N, Bésuelle P., Di Michiel M., Marello S., Desrues J.,
Kretzschmer M. (2004) - X-ray micro tomography for studying localized
deformation in fine-grained geomaterials under triaxial compression.
Comptes rendus Mécanique, 332, 819-826.
15. Lanier J., Caillerie D., Chambon R., Viggiani G., Bésuelle P., Desrues J.
(2004) - A general formulation of hypoplasticity, International Journal for
Numerical and Analytical Methods in Geomechanics, Vol. 28, No. 15, 1461–
1478.
16. Tamagnini C., Calvetti F., Viggiani G. (2005) - An assessment of plasticity
theories for modeling the incrementally non-linear behavior of granular
soils. Mathematics and Mechanics of Granular Media, ICIAM 2003, Journal
of Engineering Mathematics, in print.

Assistant Professor
Department of Civil and Environmental Engineering
Louisiana State University/Southern University
Baton Rouge, LA 70803, USA
Tel: (225)578-4821; Fax: (225)578-8652; Email: lwang@lsu.edu;
http://www.cee.lsu.edu/facultyStaff/itis.htm
My research interest is in Integrated Microstructure Characterization, Modeling
and Simulation of the Behavior of Infrastructure Materials. Civil engineering is a
very broad field. A thread that links many areas of this field is infrastructure
materials: porous medium for both geotechnical and geoenvironmental
engineering, asphalt concrete for transportation engineering, cement concrete
for structure engineering and geo-infrastructures. A large portion of the
infrastructure materials is stone based composite material. Multiple scale
microstructure characterization (including nanoscale structure), modeling,
simulation and visualization of the behavior of infrastructure materials are
fundamental and common to research of other materials in terms of
methodology. The essence of this methodology is the characterization and
representation of the real microstructure of the material, development of
theoretical models for particle level interactions, and computational simulation
of the behavior of these materials. Use of nano indentation system, x-ray
tomography and other imaging tools allows multiple scale material structure
from nanoscale such as clay particle morphology, to micro scale such as thin
film of asphalt mastics, and to meso scale such as granular/mixture skeleton be
characterized and represented for both discrete and continuum modeling and
numerical simulation. This is the main theme of the Partnership for Innovation
project funded by NSF, which applies advanced sensor networks and
information technologies for infrastructure materials research. Integration of
real microstructure into modeling and simulation unifies research on different
infrastructure materials in methodology.

1. L.B. Wang, J.D. Frost and N. Shashidhar (2001). Microstructure Study of
Westrack Mixes from X-ray Tomography Images. TRR 1767, pp85-94.
2. L.B. Wang, J.D. Frost and J.S. Lai (2001). Quantification of the Doublet
Vector Distribution of Granular Materials. ASCE Journal of Engineering
Mechanics, Special Issue: Multiple Modeling of Damage and Material
Characterization with Microstructure. Vol. 127, No.7, pp 720-729.
3. L.B. Wang, J.D. Frost. and J.S. Lai (2003). 3D Digital Representation of the
Microstructure of Granular Materials from X-ray Tomography Imaging.
ASCE Journal of Computing in Civil Engineering, Vol.18, No.1, pp 28-35.

Department of Chemical Engineering
University of Cambridge, New Museums Site
Pembroke Street, Cambridge, CB2 3RA, UK
E-mail: diw11@cam.ac.uk
Our interests lie in the deformation behaviour of the saturated and near-
saturated systems known as granular pastes, which differ markedly from the
soils which are the primary focus of this workshop. Firstly, we are interested in
these materials as soft-solids which can be readily extruded to generate
controlled shapes, so they must be able to deform and flow steadily as well as
retain their form when at rest. The materials can be pharmaceuticals, ceramic
catalysts, herbicide formulations or food products and the length scales can
vary from the sub-millimetre to the centimeter. The particles are usually in the
micron range or above and at high solids volume fractions, so that the rheology
is dominated by interparticle contacts. Secondly, these are formulated
products so there is considerable freedom in specifying the properties of the
particulate and liquid phases. The problem is that there is too much freedom
and the relationships between the bulk and interface rheology of these
materials and the components is not well established: we are therefore seeking
to construct physically-based models of extrusion behaviour and phenomena
which will guide formulation and provide a framework to overhaul the current
reliance on empirical knowledge.
These soft-solids can be modelled as soils or using fluid constitutive models,
but the latter are unable to incorporate the various phenomena that separate
these pastes from more dilute suspensions – particularly the role of the liquid
phase. Particular topics which we have been working on are (i) liquid phase
migration; (ii) wall slip; and (iii) fracture. The former is a dynamic drainage
problem, where the liquid phase moves past the solids skeleton owing to the
pore pressure generated during the extrusion process and therefore
compromise the process. A concerted study is under way, featuring
experiments on model systems, finite element analysis of extrusion using soils
models such as modified Cam Clay and discrete element modeling. It is not
possible to model paste extrusion directly using DEM so here we seek to
develop permeability functions to link the particulate scale into the process
scale.
Wall slip is frequently reported for granular pastes and dense suspensions but
poorly understood and rarely predictable. We have obtained direct evidence
of wall slip using novel data interrogation methods and magnetic resonance
imaging: this is an area awaiting micro-mechanical study in order to be able to
design it in or design it out.

Finally, surface fracture in granular paste systems can be spectacular, as shown
in the Figure, and although the phenomena observed are often related to those
observed in polymers, there are so many differences that they should be
studied in their own right. Crack propagation and stress relaxation are key
processes in extrudate fracture and a micromechanical perspective is therefore
needed.
More information on our work, and details of publications, can be found on the
Paste and Particle Processing group website:
www.cheng.cam.ac.uk/research/groups/paste.

Civil and Environmental Engineering Department
Rensselaer Polytechnic Institute, Troy, NY 12180
Phone: (518) 276-2836, Fax: (518) 276-4833, E-mail: zeghal@rpi.edu
The methodology in evaluating and predicting the response of soil systems to
external excitations is on the verge of undergoing a significant paradigm shift.
Computational simulations are destined to become more prominent than
empirical approaches and will ultimately become the main tool for analysis and
design of civil systems. I believe that future seminal advancements in the fields
of soil liquefaction and ground failure are contingent on this paradigm shift,
and that this shift requires a micro-mechanical methodology.
Saturated granular soils are multi-phase mixtures of mineral particles and fluids
filling the pores. Such soils exhibit a highly complex nonlinear response dictated
by interactions between particles and at fluid–particle interfaces. These
interactions are marked by the solid and fluid phase dissimilar physics and
engender mechanisms of multiple spatial and temporal scales. Liquefaction and
instability phenomena occur when the forces exerted by the fluid on the
particles approach or counterbalance the inter-granular forces. These
phenomena include changes in soil state from a solid to presumably a heavily
viscous suspension. The characteristics of this state transition as well as the
nature and mechanical properties of this suspension are generally difficult to
assess experimentally and remain obscure.
My interests in micro-aeromechanics reflects my conviction that a realistic
modeling of the liquefaction and failure of saturated granular soils may be
achieved by using a multi-scale, multi-physics coupled formulation capable of
accounting for the skeleton discrete deformation, pore fluid flow and resultant
interactions (Fig. 1). In this regard, I have used a continuum-discrete fluid-
particle model to idealize the dynamic response and liquefaction of saturated
granular soils on the basis of micro-mechanical considerations. I have also used
such a model to investigate the failure mechanisms of saturated cemented
granular soils. The conducted investigations shed light on a number of salient
dynamic soil response mechanisms that have remained obscure and eluded
experimentation.

1. Zeghal, M. and El Shamy, U., A Continuum-Discrete Hydromechanical
Analysis of Granular Deposit Liquefaction, International Journal for
Numerical and Analytical Methods in Geomechanics, Vol. 28, No. 14, pp.
1361- 1383, 2004 (http://www3.interscience.wiley.com/cgi-
bin/jissue/109609806).
2. El Shamy, U. and Zeghal, M., A Micro-Mechanical Study of the Seismic
Response of Saturated Cemented Deposits, Journal of Earthquake
Engineering, Vol. 9 (Special Issue 1 on Geotechnical Earthquake
Engineering), May 2005.
Figure 1. A schematic microscopic view of fluid flow through the pores of granular soil
deposit and associated continuum-discrete model.