C'est avec plaisir que nous partageons la présentation de M. Masood Meidani de l'Université McGill, lauréat du concours Branko Ladanyi pour ses travaux sur l'effort axial dans les conduites enfouies. Il remporte une bourse qui lui permettra d’assister à la 71e Conférence Canadienne de Géotechnique qui se tiendra à Edmonton du 23 au 26 septembre 2018 (http://www.geoedmonton2018.ca). Ce prix a été nommé en l'honneur de M. Branko Ladanyi, Professeur émérite à l'École Polytechnique de Montréal. Durant sa longue et fructueuse carrière, le Professeur Ladanyi a enseigné la géotechnique et mené des travaux de recherche originaux sur une variété de sujets, incluant le comportement des sables, des argiles et des roches, et le dimensionnement des fondations superficielles et profondes. Il est à l’origine de nombreuses contributions scientifiques et techniques marquantes qui sont présentées à travers plus de 200 publications. Il s'est avéré un pionnier dans le domaine de la géotechnique des sols gelés et de l'ingénierie en régions froides. Il est l'auteur, avec O.B. Andersland, du « best-seller » intitulé « An Introduction to Frozen Ground Engineering » (Chapman & Hall, 1994; Second Edition, ASCE Press et John Wiley & Sons, 2003). Ces travaux ont valu au Professeur Ladanyi une grande renommée internationale et de nombreux prix prestigieux. Il est membre de l'Académie canadienne du génie et de l'Académie des sciences de la Société royale du Canada.

1. 1/22
Branko Ladanyi 2018 competition
Performance Evaluation of Buried Pipes Subjected to
Axial Soil Movement Using Coupled Finite-discrete
Element Framework
By
Masood Meidani
Supervisors
Professor M. Meguid, Professor L. Chouinard
March 2018

2. 2/22
Introduction
Canada has almost
119’000 km
of transmission
pipelines
In 2015, $1.3 b was
spent on monitoring
and maintenance
Over the past 20 years, pipeline incidents have caused more
than $7.5 billion in property damage.
www.cbc.com

3. 3/22
Main causes of buried pipes failure
Part of failure causes are related to excavation damages, materials corrosion and
incorrect operation. But in the other hand, natural hazards such as ground
movement is a part of the problem too.
Distribution of incidents (2009–2013), 9th report of EGIG

4. 4/22
Pipe-soil interactions
Response of pipes to ground movement depends on the orientation of pipeline
with respect to moving slope.
Soil load on pipeline passing throw an area subject to land-sliding

5. 5/22
What is the problem?
• Since the early 1960s, researchers have studied soil-pipe interaction.
• The current approach to determine axial soil loads on pipes in granular soil:
ASCE (1984) 𝐹𝐴= 𝛾′ × 𝐻 ×
1+𝐾0
2
× tan 𝛿 × (𝜋 𝐷)
• Some studies showed that the recommended equation by ASCE underestimate
the maximum soil resistance on pipes buried in dense granular soil.
Pipe
σv
σh = Ko σv

6. 6/22
How can we investigate it?
This study presents
a three-dimensional finite - discrete element (FE-DE)
simulation on the response of a rigid and flexible pipe buried
in dense sand subjected to axial loading.

7. 7/22
Why Finite-Discrete Element Method (FE-DE)?
Limitations
of
FEM Capturing particle
movements associated
with pullout of buried pipe
Studying the interaction in
particle scale level
Limitations
of
DEM Modeling the structural
elements due to the
continuum behavior
DE Particle
8-Node
Hexahedral elements
Interface element
Triangular facet
DE Particle

8. 8/22
Research Methodology
Phase I
Calibration
Phase II
Validation
• Comparing the stress around the pipe in rest
condition with the results of analytical
methods
• Comparing the results of simulated pullout
test of buried pipe with the experimental data
Finding input parameters of DEM by comparing the
result of simulated triaxial test with laboratory tests
data
Phase III
Simulations
Creating a model of buried pipe in granular soil
and imposing axial soil movements

9. 9/22
Numerical Simulation
Specific gravity 2.72
Young’s modulus, Ei (MPa) 40
Unit weight (kN/m3) – (75% relative density) 16
Internal friction angle  (Degree) 45
Cohesion (kN/m2) 0
Poisson ratio, υ 0.3
Porosity, η 0.41
Backfill material – Fraser River Sand
Young’s modulus, Ei (MPa) 2e+5
Unit weight (kg/m3) 8000
Interface friction coefficient 0.8
Diameter (mm) 46
Thickness (mm) 13
Young’s modulus, Ei (MPa) 550
Unit weight (kg/m3) 900
Interface friction coefficient 0.6
Diameter (mm) 114
Thickness (mm) 10.3
Rigid steel pipe Flexible MDPE pipe

10. 10/22
Numerical model generation – Rigid Steel pipe

11. 11/22
Numerical model generation – Flexible MDPE pipe
X
Y
Z
(Pullout
direction)
0.5m
Y
Z
0.5 m
0.5m
Pipe, D=114 mm
Pipe
3.85 m
Thickness = 10.3 mm
114 mm
Interface
element
Front end
2.25 cm5 cm
X
Y
Z
(Pullout direction)

12. 12/22
Calibration of the model
A calibration procedure is required to determine the input parameters for a given
soil condition before it is adopted in the DEM.

13. 13/22
Validation of the model
Comparing Initial earth pressure distribution on the pipe (kPa)
Rigid steel pipe:

14. 14/22
Results – Soil response to pipe movement
1- Rigid steel pipe:
• Significant discrepancies between the guidelines’ prediction value and the measured one.
• It has been found that the entire length of the pipe start moving after 4 mm movement
of the front end.
• Soil friction can be considered uniform along the length of the pipe
• The pullout test on a steel pipe can be assumed as an “element test”.

15. 15/22
Results – Earth pressure distribution around the steel pipe
• The increase in axial pullout force is attributed to the increase in normal stresses due to
the dilatant behaviour of the sand under interface shear deformations

16. 16/22
Results – Contact force network around the steel pipe

17. 17/22
Results – Soil response to pipe movement
2- Flexible MDPE pipe:
• The peak axial soil resistance is more than the guideline's prediction.
• That section of the MDPE pipe which slipping occurs increases progressively as the
pullout force is increased.
• The frictional resistance along the MDPE pipe is not uniform.
0.00
0.30
0.60
0.90
1.20
1.50
1.80
2.10
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Pulloutforce(kN/m)
Displacement at leading end (mm)
Numerical simulation
ASCE (1984)
Trailing end of the
pipe starts moving

18. 18/22
Results – Horizontal displacement of MDPE pipe
• We cannot define a unique Xmax (displacement required to reach the peak axial
resistacne) for PE pipe.
• The PE pipe in this study should be considered as "model test" not "element test" as
would be the case for test on rigid steel pipe.
Horizontal
Displacement (mm)
14
12.5
11
9.5
8
6.5
5
3.5
2
0.5
(Pullout direction)X
Y
Z

19. 19/22
Results – Soil particles movement around the MDPE pipe
X
Z
0.5 m
3.8 m
Pullout direction
Pipe, D= 114 mm
Displacement field of the soil domain at Ux= 14 mm

20. 20/22
Results – Contact force network around the MDPE pipe
Y
X
Zone A
Zone A
Pipe pullout
direction
Pipe pullout
direction
a)
b)
a) initial condition (before pullout)
b) after pullout at Ux=14mm

21. 21/22
Takeaways
1. The equation recommended in ASCE (1984) needs to be used with caution to calculate
axial soil resistance on a buried pipe placed in a relatively dense sand material.
2. The increase in the soil stresses acting on the pipe under pulled loading condition can be
explained by the dilation of the dense sand during shear deformation.
3. The frictional resistance on steel pipe can be considered as a uniform load along the pipe
length.
4. In MDPE pipe, most of the pipe deformation and strain occurs close to the front side of
the pipe and they progressively decrease to the far end. This finding is in contrast with
commonly used guidelines method which considers the pipe as a rigid element and
assumes the frictional resistance is mobilized along the entire length of the pipe.
5. The coupled FE-DE framework in an efficient method in validating geotechnical problems
involving granular material and large deformations.

22. 22/22
Thank You!