educational session geosynthetics in reinforced soil ... · pdf filegeosynthetics in...

Geotechnik im Bauwesen Geotechnical Engineering Univ.- Prof. Dr.-Ing. Martin Ziegler

1 Educational session Geosynthetics in reinforced soil structures

Educational session

Geosynthetics in reinforced soil structures

AOR Dipl.-Ing. Gerhard Bräu

Univ.-Prof. Dr.-Ing. Martin Ziegler Geotechnik im Bauwesen, RWTH Aachen University



Educational session

Geosynthetics in reinforced soil structures

1. Introduction: Functioning of geosynthetic reinforcement in soil (M. Ziegler)

2. Introduction: Overview of EBGEO (G. Bräu)

4. Example: Earth dam (G. Bräu)

3. Example: Geosynthetic reinforced retaining wall (M. Ziegler)



Supported by

1. Introduction

2. Applications of Ground Reinforcement

3. Interaction between Reinforcement and Soil

Functioning of geosynthetic reinforcement in soil

Univ.-Prof. Dr.-Ing. Martin Ziegler Geotechnik im Bauwesen, RWTH Aachen University

4. Summary and Conclusions



1. Introduction



1. Introduction

http://www.baunetzwissen.de/objektartikel/Beton-Haus-fuer-Musik-und-Musiktheater-in-Graz-A_775168.html?img=3&layout=galerie

http://bauwiki.tugraz.at/bin/view/Baulexikon/BeWehrung



1. Introduction

Courtesy Huesker



1. Introduction

Temple Ziggurat in Aqar Quf (Mesopotamia, near Bagdad) 1500-1300 B.C.

Stabilisation of foundation and brick walls with reed mats

Vogt/TUM



1. Introduction http://upload.wikimedia.org/wikipedia/commons/3/33/Pantheon_innen.jpg

http://de.wikipedia.org/w/index.php?title=Datei:Roemerkanal_buschhoven.jpg&filetimestamp=20050602123409

Invention of Opus Caementitium - ancestor of concrete (1 century AD) Pantheon Rome

Segment of the 116km long old Roman Eifel water-channel (1 cent. AD)



2. Applications

Reinforcement of base course

Foundation cushion

Railway and roadworks

Embankments

Bridge abutment Steep slopes

Applications of ground reinforcement

Pile foundation Bridging of sinkholes



2. Applications

Retaining wall with geogrids (Netlon LTD. UK)



2. Applications

Courtesy Huesker



2. Applications

Slope stabilization in Trento Italy

Courtesy Huesker



2. Applications


Foundation cushion


Embankments






2. Applications

Bridge abutment

Bridge abutment at Ullerslev, Denmark, 1991 Maybe the first geogrid reinforced bridge abutment in Europe

Courtesy Huesker



2. Applications

First permanent bridge abutment in Germany with geogrid reinforced

earth and gabion-facing Ilse bridge, 2000

Courtesy IBH Herold

geogrids

gabion 80/15

0

non w oven fabric for separation

f illing of reinforced area 0/45

Huesker Fortrac

140/30-30 MP

Huesker Fortrac

140/30-30 MP

Geogrid reinforced construction w ith gabion

facing

support construction precast

concrete girder



2. Applications


Foundation cushion


Embankments






2. Applications

Courtesy Tensar

Stabilization of a site road with geogrids combined with a nonwoven



2. Applications

Stabilization of a site road with geogrids in combination with a nonwoven fabric

unreinforced reinforced

Courtesy Bräu

Courtesy Bräu



2. Applications Courtesy Huesker

Courtesy Huesker

Courtesy Naue Courtesy Naue

Use of geogrids and geotextiles over soft soil under the base course



2. Applications


Foundation cushion


Embankments






2. Applications

Embankment on cemented stone colums in soft soil

Paulinenaue: German Rail 2003 cross section with two geogrid layers

Courtesy Huesker



2. Applications

Selby Bypass, UK, 2002 Mixed solution Geogrids FORTRAC M (PVA) & FORTRAC (PET)

Courtesy Huesker

Courtesy Huesker

Embankment on reinforced concrete piles in soft soil

Courtesy Huesker



2. Applications

Geosynthetic encased sand-columns



2. Applications

courtesy Möbius

courtesy Möbius

Manufacture of geosynthetic encased

sand-columns

courtesy Möbius



2. Applications

Foundation of an embankment on geosynthetic encased sand columns – land reclamation Deutsche Airbus, Mühlenberger Loch



2. Applications

October 2001, courtesy Airbus Deutschland GmbH

Land reclamation – Airbus Mühlenberger Loch



2. Applications


Foundation cushion


Embankments






2. Applications

Collapse sink phenomena



2. Applications

Highway A 143, Germany, 2004, Fortrac R 1200/100-10 AM

Courtesy Huesker

Bridging of sinkholes with high-strength geogrids

Courtesy Huesker



2. Applications

Coverage of tailings-pond

tailings - pond

ringdyke geogrid coverage

Courtesy Naue Courtesy Naue

Courtesy Naue



3. Interaction

Field test at a temporarliy abutment highway A8 (Germany)

(Bräu a. Floss, 2000)

measured: h >> 1,4

h = 1,4 calculated: Stability analysis (global)

Enlargement of bearing capacity



3. Interaction

Jablonec nad Nisou - Střelnice

Extensometr No.1

0,00%

0,10%

0,20%

0,30%

0,40%

0,50%

1 100 10000

Days (log scale)

Str

ain

(%

)

2,0

4,0

7,0

10,0

=0,4% 2m over GL

4m over GL

10m over GL

3 years

Strain - measurement with extensometers in different layers (Herle 2006)

Enlargement of Jablonec-Střelnice Stadium

Reduction of deformations

courtesy Herle

courtesy Herle



3. Interaction

M = 4 Ql

l/2 l/2

crack reinforcement bar

Q theoretical stress distribution detail

M

complete bond

Load transfer in a reinforced concrete beam

P

T

real load transfer

bending moments

-

+



3. Interaction

3

Z

2

1

3 2 = 3

1 2

3

1 soil metal 1

3

2

deviatoric plane

limit state surface

O

P D

1 = 2 = 3

Principal stress state

1 = 2 = 3



3. Interaction

1 = 2 = 3

D

3

deviatoric plane

Z

2

1

2 = 3

limit state surface

m

1

2·3

1 = 2 = 3

possible stress-states

not possible

not possible

Principal stress state

3 2 = 3

1

isotropic path: high stresses, low deformation

deviatoric path: approaching limit state, high deformation

O

P

favourable



3. Interaction

Large triaxial compression test apparatus (Ø 500mm)

3 (vacuum)

hydraulic plunger

D = 0,5m

DU

elastic cover

base course 0/45

geogrids

measuring band

loading plate

H ≈ 1,1m



3. Interaction



3. Interaction

unreinforced

Geogrids

reinforced

σ1,unreinf. = σ1,reinf.

εunreinf. >> εreinf.



3. Interaction

Radial Strains



3. Interaction

Radial Strains

Confining Effect of the Reinforcement



3. Interaction

Interlocking effect

increasing lateral pressure with increasing load without remarkable deformations

Courtesy Huesker

Courtesy Naue



3. Interaction

courtesy Naue

The effect of interlocking mechanism



3. Interaction

σ3 σ3

σ1

σ1

Stress path for unreinforced triaxial testing (CD)

σ3 = σc

σ1

[kN/m²]

σ3

[kN/m²]



3. Interaction

Freinf. Freinf.

∆σ3 ∆σ3

σ3 σ3

σ1

σ1 new failure point

Δσ3

σ1

[kN/m²]

σ3

[kN/m²]

Δσ1

Δσ1

Activation of the

Reinforcement

∆σ3: Additional

Confining Effect

∆σ1: Increase of the Load

Bearing Capacity

Δσ1

σ3

Stress path for reinforced triaxial testing (CD)



3. Interaction

3 1

= · tan

3+D3 1+D1

failure point without reinforcement

failure point with reinforcement



3. Interaction

0,12m

0,2m Tragschicht

0,8m

1,0m

“Weichschicht”

Tragschicht

“Weichschicht”

0,12m

2 x 0,1m

Geogitter

0,8m

1,0m

Test Set-Up for the comparison of a unreinforced and a reinforced bearing layer

Load Bearing Layer

“Soft Soil“

Load Bearing Layer

“Soft Soil“

Geogrid



3. Interaction

Better Load Distribution leads to less loading of subsoil

unreinforced reinforced

soft soil soft soil

bearing layer bearing layer geogrid



3. Interaction

0

20

40

60

80

100

120

0 100 200 300 400 500 600Fu

nd

ame

nts

etz

un

g [m

m]

Fundamentlast [kN/m²]

unbewehrt

bewehrt

270 kPa

Footing Stress [kPa] Fo

otin

g Se

ttlem

ent

[mm

]

unreinforced

reinforced Ds

Different settlements for unreinforced and reinforced subgrade at the same load



3. Interaction

v h

Q

v

v=h

h0

1

h=K0∙v

h=Ka∙v

v0

h

Stress paths under a runnning wheel



3. Interaction

Q

v

unreinforced subgrade

h

Dh1 Dv

v

v=h

h0

1

h=K0∙v

h=Ka∙v

v0

vQ

h

2

hQ




3. Interaction

Q

v

unreinforced subgrade reinforced subgrade

h

Dh1 Dv

h v

geogrid

v

v=h

h0

1

h=K0∙v

h=Ka∙v

v0

vQ

h

2

hQ

h0

v0

h

1




3. Interaction

Q

v

unreinforced subgrade reinforced subgrade

h

Dh1 Dv

h v

geogrid

v

v=h

h0

1

h=K0∙v

h=Ka∙v

v0

vQ

h

2

hQ

h0

v0

h

1

Q

Dh2 > Dh1

Dv

vQ

hQ

2




3. Interaction

Test Set-Up

σ1= 50kPa

Development and distribution of the earth pressure on the wall facing

Kinematic behaviour of soil grains



3. Interaction

-1/3 Ea

No extra deformation required for geogrid activation!

Development of earth pressure



3. Interaction

Digital Image Correlation (DIC)

from: Tropea et al. (2008)

Particle displacements Particle rotations



3. Interaction

Sliding Planes

0

rot.

Geogrids: unreinforced



3. Interaction

less soil moving

increasing reinforcement

less earth pressure!

unreinforced

2 Geogrids

5 Geogrids

Sliding Planes



3. Interaction

DIC-results (detail section)

max

0

horizontal displacements

no displacment

max. displacement

(geogrid not connected to facing)



3. Interaction

Corresponding kinematic model

(failure plane of unreinforced soil)

unconfined soil

Zone of major failure planes

Detail section Geogrids

Primary sliding body

Secundary sliding body

Geotechnical Engineering Univ.-Prof. Dr.-Ing. M. Ziegler


from: www.depechemode.de

“road blocks“

Illustration of the “reinforcing effect“



4. Summary and Conclusions

Summary and conclusions

- Ground reinforcement (with geosynthetics) is an effective way to increase the bearing capacity of different geotechnical constructions

- Under equal load the deformations of a reinforced construction are much less than the ones of an unreinforced one

-The increase in bearing capacity and the decrease in deformations can be explained by the change of the high deviatoric stress state in the unreinforced case to a more isotropic one in the reinforced state.

- This change is caused by the interlocking effect of the geogrid which enables the increase of an equivalent confining stress without remarkable deformations.



Tests in Kyushu, Japan

Thank you for your attention

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