The Future of the DiscreteThe Future of the DiscreteElement Method inElement Method in

Infrastructure AnalysisInfrastructure Analysis

Raju KalaJohannes L. Wibowo

John F. Peters

Finite Elements Imply ContinuityFinite Elements Imply Continuity

Challenges in Failure MechanicsChallenges in Failure Mechanics

Large deformations withdiscontinuities are difficult to modelby conventional finite elements.

Simply having a factor ofsafety not enough.

Particle Methods for LargeParticle Methods for LargeDeformation ProblemsDeformation Problems

• The trap door experiment is aclassical geotechnicalproblem from earth pressuretheory

• Soil behavior ranges fromsolid to flowing fluid.

• Particle methods are anatural way to address suchproblems

Discontinuous ShearDiscontinuous Shear

• The passive resistance to motiona rigid wall into sand is anexample of very largedeformation

• The discontinuous nature of themotion at the base of the wall isespecially challenging fortraditional numerical methods.

Numerical Methods forNumerical Methods forMobility ModelingMobility Modeling

• Vehicle mobility mechanics has muchin common with failure mechanics ingeotechnical engineering.

• Recent advances in particle methodsfor mobility modeling hold promise forfailure mechanics in geotechnicalapplications.

Particle ModelingParticle Modelingwith the Discretewith the DiscreteElement MethodElement Method• DEM depicts the soil

as individual particlesrather than connectedelements.

• The particles move inaccordance to simpleinteraction laws ratherthat complicatedconstitutive models.

DEM MechanicsDEM Mechanics• Physics based• Replicates particulate

nature of soil• Slip planes and

separations form betweengroups of particles thuscapturing evolving failuremechanisms morerealistically

k

Discrete Particle System

m

f1

f2f3

f4 Fi

nivi

Forces Acting on Particle k

force acceleration velocity displacement

Interaction with Finite ElementInteraction with Finite ElementStructuresStructures

NodeNode

LineLine

N1 FF

N2 FF

FF

N1 + N2 +N3 =1

N3 FFElementElement

10

2030

405060

2 2.5 3 3.5 4Plow Distance , cm

Plow

For

ce, g

ram

s

0.5 1 1.5

SimulationOttawa 20-30Glass Beads

.5 1.5100

Simulation of Wall ExperimentSimulation of Wall Experiment

X Location (mm)

YL

ocat

ion

(mm

)

10

15

20

25

30

35

65 70 75 80 85 90 95

SimulationSoil Test

General character of deformation wasreproduced well.

Quantitative agreementwas achieved fordisplacement and force.

Simulated Laboratory ExperimentSimulated Laboratory ExperimentSterss Vs. Vertical Strain

0

10000

20000

0 0.1 0.2

Vertical Strain

Stre

ss

Volumetric Strain Vs. Vertical Strain

0

0.1

0.2

0.3

0.4

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Vertical Strain

Vol

umet

ric

Str

ain

Simulate specimen afterformation

Simulated stress-strain andvolume change curves

Modeling Large DiscontinuousModeling Large DiscontinuousDeformation with ParticlesDeformation with Particles

• Bearing CapacityProblems

• Penetrometers• Slope Stability

Where is DEM Research GoingWhere is DEM Research Going

• Cohesive particles for slope stability problems• Asphalt property test simulation• Vehicle-soil interaction• Water-soil interaction• Non-spherical particles

Future of DEMFuture of DEM

• Earth pressure and slope stability problemswith soil-structure interaction

• Consequences of failure• Piping and fines migration• Spillway erosion

Raju.V.Kala@ERDC.USACE.ARMY.MILRaju.V.Kala@ERDC.USACE.ARMY.MILPhone : 601 634 2219Phone : 601 634 2219

John.F.Peters@ERDC.USACE.ARMY.MILJohn.F.Peters@ERDC.USACE.ARMY.MILPhone : 601 634 2590Phone : 601 634 2590

Thank YouThank You