2nd International FLAC/DEM Symposium

2nd International FLAC/DEM Symposium

Lateral Earth Pressures with

Layered Backfill

Jim S. Shiau, PhD (Newcastle)

Senior Lecturer in Geotechnical Engineering

Faculty of Engineering and SurveyingUniversity of Southern Queensland

Toowoomba, QLD, Australia

7/13/2011 Dr. Jim Shiau 2

USQ, Toowoomba, Queensland, Australia

1.5 hr drive to Brisbane

2.0 hrs drive to Gold Coast

13 July 2011 Dr. Jim Shiau 3

Background to research

To make use of the existing resources at USQ ( both 2D and 3D

FLAC licences), we aim to develop numerical models for various

geotechnical applications.

Research at USQ also involves developing various physical models

for teaching purposes, so as to complement the numerical

approach using computer modeling.

Dr. Jim Shiau 4


USQ Geotechnical Stability Testing Rigs

P

Δ

Pu

13 July 2011



What is physical model?

A landslide model to

simulate the failure pattern

of a slope.


Bonsai vs. Physical Model

The knowledge gained in the

process of Bonsai making would

help to understand the behaviour

of a real tree.

Bonsai


USQ Geotechnical Stability Testing

Rigs


Various Stability Models using FLAC

Classical earth pressure problems

Slotted wall

Trapdoor

Tunnel heading

Uplift of buried pipe

Uplift of ground anchor

FLAC (Version 4.00)

LEGEND

8-Jun-06 20:23

step 72142

-1.111E+00 <x< 2.111E+01

-7.111E+00 <y< 1.511E+01

Max. shear strain-rate

0.00E+00

2.80E-08

5.60E-08

8.40E-08

1.12E-07

1.40E-07

1.68E-07

1.96E-07

2.24E-07

Contour interval= 7.00E-09

-0.400

0.000

0.400

0.800

1.200

(*10^1)

0.200 0.600 1.000 1.400 1.800

(*10^1)

JOB TITLE :

USQ

USQ

FLAC (Version 4.00)

LEGEND

8-Jun-06 14:22

step 75374

-4.444E-01 <x< 8.444E+00

-1.444E+00 <y< 7.444E+00


0.00E+00

6.00E-08

1.20E-07

1.80E-07

2.40E-07

3.00E-07

3.60E-07

4.20E-07

4.80E-07

5.40E-07


-0.500

0.500

1.500

2.500

3.500

4.500

5.500

6.500

0.500 1.500 2.500 3.500 4.500 5.500 6.500 7.500

JOB TITLE :

USQ

FLAC (Version 4.00)

LEGEND

6-Jul-06 20:30

step 100000

-3.900E-01 <x< 7.410E+00

-2.400E+00 <y< 5.400E+00


0.00E+00

3.70E-07

7.40E-07

1.11E-06

1.48E-06

1.85E-06

2.22E-06

2.59E-06

2.96E-06

3.33E-06


-1.500

-0.500

0.500

1.500

2.500

3.500

4.500

0.500 1.500 2.500 3.500 4.500 5.500 6.500

JOB TITLE :

USQ

USQ

FLAC (Version 4.00)

LEGEND

8-Dec-04 16:35

step 5500

-3.333E+00 <x< 3.333E+00

-2.833E+00 <y< 3.833E+00

Material model

mohr-coulomb

Velocity vectors

Max Vector = 1.005E-04

0 2E -4

Boundary plot

0 2E 0

-2.000

-1.000

0.000

1.000

2.000

3.000

-2.500 -1.500 -0.500 0.500 1.500 2.500

JOB TITLE :

Computational Engineering Researc



Had some experience in Upper and Lower Bound Limit Analyses

during my stay in Newcastle Geotechnical Group during 1998-

2003.

Overall, my research interests at USQ

• To develop stability models using FLAC.

• To develop stability models using Upper and Lower limit analyses.

• Physical modeling using simple stability testing rigs at USQ.

Two papers in this symposium:• Modeling Uplift of Plate Anchor

• Earth Pressures with Layered Backfill

7/13/2011 Dr. Jim Shiau 11

Goal and Objective

Lateral Earth Pressures with Layered Backfill

To investigate the situation of active and passive earth

pressures on the back of a retaining wall with layered backfill.

To compare FLAC results with those using classical earth

pressure theory and FE Limit Analyses - Upper and Lower Limt

Analyses.

• FLAC

• Rankine/Coulomb/Log Spiral

• Upper and Lower bounds

For smooth and rough wall cases!

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The problem definition

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The problem definition

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To solve a static system using the dynamic equation of motion, an

artificial nodal damping is needed so that kinetic energy can be

gradually removed.

Smooth case - Active wall

FLAC solution

Textbook solution – Rankine

Upper and Lower bound solutions

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Textbook solution of the problem

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Active wall – smooth wall case – Rankine’s solution

2.71 kPa

25.46 kPa

16.12 kPa

73.16 kPa

Active Pressure Diagram

Rankine: Total horizontal active thrust = 176.18 kN/m

FLAC solution = 167.20 kN/m

Upper and lower bound solutions of

the problem

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Active wall – smooth wall case

FLAC solution

= 167.20 kN/m

Smooth case - Passive wall

FLAC solution

Textbook solution – Rankine


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Textbook solution of the problem

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Passive wall – Smooth wall case – Rankine’s solution

36.9 kPa

219.6 kPa

93.0 kPa

140.2 kPa

Active Pressure Diagram

Rankine: Total horizontal passive thrust = 734.55 kN/m

FLAC solution = 744.50 kN/m


the problem

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Passive wall – smooth wall case

FLAC solution

= 744.50 kN/m

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Rough case - Active wall

FLAC solution

Textbook solution – Coulomb


7/13/2011 Dr. Jim Shiau 22


the problem

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Active wall – rough wall case

FLAC solution

= 127.60 kN/m

Rough case - Passive wall

FLAC solution

Textbook solution – Coulomb


7/13/2011 Dr. Jim Shiau 24


the problem

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Passive wall – rough wall case

FLAC solution

= 837.20 kN/m

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Results Summary

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7/13/2011 Dr. Jim Shiau 28

Summary

FLAC results favorably compared with upper and lower bound

solutions in all cases.

Classical earth pressure theories favorably compared with FLAC

and upper and lower bound solutions only in smooth wall cases

(active and passive) and rough active wall case.

For the rough passive wall case, the log-spiral failure surface

Shields & Tolunay’s (1973) theory is not particularly accurate for

the layered problem. It’s on the unsafe side with some 20%

overestimation ~ needless to mention Coulomb’s solution with

linear slip assumtion.

7/13/2011 Dr. Jim Shiau 29

Future Work

• Pressure distribution behind the wall.

• Velocity jump and change of velocity direction across layered

media.

• Shear stresses across the layered media for the passive + rough

wall case

Documents

2nd International FLAC/DEM Symposium