10/09/2016

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Emeritus Prof.Jean-Pierre Gourc jean-pierre.gourc@univ-grenoble-alpes.fr

LTHE - Université Grenoble Alpes – France

UMR 5564 CNRS,INPG,IRD,UJF

Training Course September 2016

Prof.Delma Vidal delma@ita.br

Instituto Tecnológico de Aeronáutica - Brasil

-F-

Lateral barrier of landfill F-1 Presentation of a Geosynthetic Lining System (GLS)

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Trend to stiffen

slopes

For social and economic reasons, Landfills are becoming higher

with stiffer slopes

Stability problems linked to composite barriers on slope are increasing

Geosynthetic Lining Systems

are a relevant solution as Barriers to confine waste , specifically on slopes

where they are easier to lay than mineral layers

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Installation of a Geosynthetic Lining System (GLS) on landfill cap cover Typical Geosynthetic Lining System (GLS) on Cap cover slope

cover soil

waste

drainage

sealing

reinforcement GR

GS

GM

Concept : ONE geotechnical function ONE geosynthetic

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(Sealing)

GTr

GS

GM (Drainage)

Veneer soil

(Filtration and Reinforcement)

Slope stability assessment is complex due to the multi-components of the geosynthetic liner system

Waste

interfaces properties are required

Geosynthetic sealing layer (GM)

Geomembrane

Geosynthetic Clay Liner

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cRecycled rubber crumb drainage geosynthetic

Geotextile

(non-woven)

Geospacer for Drainage (GS)

Geonet

cm

Geogrid

Reinforced Geotextile

Geosynthetic for reinforcement (GTr)

The stability of GLS on slope only appears to be easy…

Numerous

observed failure cases demonstrate

that this problem should be studied carefully

12 G.N. RICHARDSON

Example of sliding of soil cover on geosynthetic

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-A relevant design considers a Geosynthetic Lining System where every geosynthetic is dedicated

to a UNIQUE FUNCTION: - Geomat Erosion control

- Geomembrane GM Sealing

- Geosynthetic of Reinforcement GTr Reinforcement of

the veneer soil layer

- Geospacer Drainage

F-2 Mechanism of interaction

between the different components

of the Geosynthetic Lining System

Anchorage of geosynthetics

at the top edge

Tangential stress at the interfaces

Overall stability problem

for a Geosynthetic Liner System (GLS) on slope

Veneer soil layer

Smooth and Textured Geomembranes

(HDPE)

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Elementary case of slopy cap liner:Veneer soil directly on the Geomembrane

local tensile mobilisation of the geomembrane , due to the different mobilization of

frictional stress between upper and lower interfaces

Shear stresses induced

by soil cover

Soil base

TGM

Soil base

Tensile force

in the Geomembrane

DTup

GM

DTGM

=DTup - DTdown DTdown

GM

Tensile mobilization in the geomembrane

fgs

W

R

TGM up

S’ S W’

R’

fs

Limit Equilibrium of a cap cover on slope A VERY SIMPLE MECHANISM ! ?

Block 1

Block 2 (possibly)

anchorage

slope

TGMMax

possibleTGTr

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Smooth and Textured Geomembranes

(HDPE)

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Textured surface on the lower interface decreases TGM

Textured surface on the upper interface increases TGM

Reinforcement of the Soil Cover by a basal Geosynthetic (GTr)

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To mitigate the tensile force in the Geomembrane GM a Geotextile of Reinforcement (GTr)

+ GM smooth upper interface: tGTr/GM decreases

GM textured lower interface : tGM/Soil increases TGM decreases

b

Sol

GTr

GM

TGTr

TGM

fgs

Wt

S’

W’

R’

fs

TGM

Wn

TGTr

Geosynthetic GTr decreases the friction above the Geomembrane ( and Tup

GM) decreasing the Friction Geomembrane / Cover

S

Due to -the difficult assessment of interfaces fiction -the influence of field conditions of implementation of the GLS -… It’s honest to confess that is impossible in a serviceability state to give an accurate value of the tensile forces mobilized in every geosynthetic of the GLS. It’s only possible to give an overestimation of these tensile forces ,corresponding to the ultimate limit state

Conditions acting upon theTensile mobilization of the GLS components

-Anchorage stiffness-

GLS Anchorage Pull-out Strength

u0

T0

u0

0 T0 (u0)

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Conditions acting upon theTensile mobilization of the GLS components

-Interface friction-

Relative displacement

between geosynthetics

t

uGTr

uGM t

GTr

GM

( uGTr – uGM )

Elasto-plastic Interface friction

upward

downward

Conditions acting upon theTensile mobilization of the GLS components

-Operation mode-

F-3 Assessment of the interface friction

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Waste

Compacted Clay

Liner

Geomembrane (GM)

Geotextile for reinforcement

(GTr)

Cover soil

Vegetation

Geospacer

(GS)

Vegetation Cover soil Geotextile Geoespacer Geomembrane Compacted Clay Liner Waste

GLS :Several Interfaces Soil / Geosynthetic and Geosynthetic/Geosynthetic to test

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Two different devices for tests on interface friction

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b(t)

w

q

d (t)

Inclined (or Tilting) Plane

Interface 700 x 180 mm²

Shear Box

Interface 300 x 300 mm²

sable

s

30

b

Displacement d

Lower Geosynthetic

Upper box

(Soil or Upper Geosynthetic)

Lower box

(Geosynthetic) Weight W

The Inclined Plane test (IP) is generally preferred to the Shear Box (SB) test

for this application

Normal stress for the IP device s < 10 kPa

Inclined Plane test on multi-layers barrier

(Cemagref)

Actual thickness of cover soil + Actual GLS structure can be used in laboratory

(Cemagref)

Inclined Plane test on multi-layers barrier

Before limit inclination βS

Sliding for β = βS

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Inclined plane device at LTHE laboratory

Control of β rate

Upper box

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Friction test on interfage Geosynthetic/Geosynthetic

w b(t)

géosynthetics

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Parameters deduced from an IP test

bo

bo

so =3 kPa

s = socosb

bs b50

b

d

50mm f50stat b50 European standard

b

Gradual sliding

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The careful analysis of the I.P. diagrams is capable of providing far more information than the friction angle f50 !

Shear Box Inclined Plane

t/s’

u

tan fp gg

b

fgg

bs

US

u

Correlations between data resulting of S.B. and I.P. tests should be deepened

tan frgg

Relation with fpgg and f

rgg ?

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Typical values of the interface friction angle

F-4 Anchorage conditions

& pull-out strength

Anchorage of geosynthetics

at the top edge

Tangential stress at the interfaces

Anchorage corresponds

to the max.Tensile Force in the Geosynthetics

Veneer soil layer

Tanchorage

Anchorage of Geosynthetic Lining Systems

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41

Anchorage trench for geosynthetic Lining System

Anchorage

Friction

Soil layer

β

T (β)

T (0)

Tb

Ta

Waste

Anchor trench

T

t

Geosynthetic

max

Different shapes for the Anchorage of Geosynthetic Lining Systems

Anchor Block Traction system

Geosynthetic

Soil

Pulley

Winch

Metal clamp

1 m

H D

B L

b

1.5

m

Side wall

Laboratory tests about pull-out strength of the anchorage

( L. Briançon )

0

5

10

15

20

25

30

35

0.00 0.05 0.10 0.15 0.20 0.25

U 1 (m)

T0 (

kN

/m)

Silt

T’

T

l

B

D

H

L

L2

b TA1 TA2

TA3

L1

Anchorage capacity T = TA1 + TA2 + TA3

Conventional rough design method for evaluation of the Anchor strength

Effect of the angles on the anchorage strength is assumed negligible :

No “Pulley” effect

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Alteration of the tensile force at the Anchorage Bend - « Mechanism of Frictional Pulley »-

0 m

T’3 T3

T’3

T2

T’2

T’1 T2 T’1

T1

T3

T’2

P3

P2 P1

β

T'

T

( φg = 34° )

T = T' × e tanφg

Multiplier effect on the Tensile Force

1.0

1.5

2.0

2.5

3.0

0 20 40 60 80 100

T / T’

β

Multi-anchorage process for GLS on slope with berms

Upper slope Lower slope

Berm

Width 5m

Geomembrane

Geogrill

20 cm

Veneer soil

1 m

1 m

30 cm max

Ancrage intermédiaire de l’étanchéité sur les flancs (Source ANTEA) (ANTEA)

Sketch of the intermediate anchorage of the GLS for long slopes

F-5 Geospacers

& drainage on slope

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49

Waste

Compacted Clay

Liner

Geomembrane (GM)

Geotextile for reinforcement

(GTr)

Cover soil

Vegetation

Geospacer

(GS)

Vegetation Cover soil Geotextile (FILTER) Geoespacer (DRAIN) Geomembrane Compacted Clay Liner Waste

Geospacer for collection of rainfall water

Geocomposite (Geospacer+Filter)

Geomembrane

Geogrid

Huesker

Geogrid

Geospacer + Filter

Géomembrane

Géotextile de protection

Géocomposite de drainage

Géogrille d’accroche terre

Légende

Geosynthetic Liner System on slope

Geogrid for Reinforceent

Geocomposite for Drainage

GLS with Soil Veneer

Huesker

Geospacer

Geonet Geodrain

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Different kind of Geospacers

Recycled Polymers used as a Drainage Geocomposite

Improvement of collected water,due to rainfall: intermediate collectot pipe Significance of a correct design of the Geospacer

Influence of hydraulique pressure on the activating of a soil layer sliding

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Rainfall

Correct design of the Geospacer

(modified JPGiroud,2006)

GeoSpacer

No hydraulic pressure in the veneer soil layer

Drain not full

Drain full

Unsatisfactory Collection of the run-off water

Positive hydraulic pressure in the veneer soil layer

Influence of a partial saturation of the veneer soil layer on its stability

gh = gsat = 20 kN/m3

(H1) Interface soil/soil c’ = 3 kPa f’ = 28°

(H2) Interface geos/soil: c’ = 0 fgs’ = 25°

Slope b = 20°

Depth of the sliding interface (interface geosynthetic/soil):

z = 0.8 m

Two conditions of drainage are considered:

Drainage of the run-off water

(perfect drain ) (zw = z)

Water untill a depth 0.4 m

(saturated drain ) (zw = 0.4 m)

zw

W = g L z

s = g z cos2b

t = g z sinb cosb

u = gw (z –zw) cos2b

GM

GS

GM:Geomembrane

GS : Geospacer

Stability Chart for Stability of Infinite Slope

Partially saturated Dry : ru=0

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F = c / (gz sinb cosb) + [(g’/g). + (gwzw/gz)]. (tanf /tanb)

zw = 0.8 m --> ru = 0 et A =1 F =2,04 (H1) 1,28 (H2) [perfect drain-unsaturated ]

zw = 0.4m --> ru = 0,24 et A =0.75 F =1,68 (H1) 0.96 (H2) [saturated drain , water table 0,4m) Sliding at the interface soil-geosynthetic (zw = 0,4m) excepted in case of efficient GTr)

Value of the Safety Factor F from Chart

F = [tlim ] / t = [c’ + (s-u) tanf’ ] / t

W = g L z

s = g z cos2b

t = g z sinb cosb

u = gw (z –zw) cos2b

F-6 Cap cover

Steepening of Slopes

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REINFORCED LANDFILL (Neydens’landfill)

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REINFORCED LANDFILL (Neydens’landfill)

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BABYLON LANDFILL

The Hanging Gardens of Babylon

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MULTIPLE REINFORCED-SOIL STRUCTURE

JE

RS

EY

S

T.

FE

NC

E

EL

EV

AT

ION

(m

)

REINFORCEDSOIL SLOPECOVER SYSTEM

CONVENTIONALCOVER SYSTEM

EXISTING GROUND

ADDITIONAL FILL

EXCAVATED WASTE

CRITICAL FAILURE SURFACE

AREA OF WASTE FILL

0

36

60

42

48

54

150m90m60m30m

Babylon Landfill, New York

PRIMARY REINFORCEMENT

GAS COLLECTION SAND

REINFORCED SOILSLOPE FACE WRAP

STRUCTURAL

FILL

SECONDARY REINFORCEMENT

GEOMEMBRANE

GEOMEMBRANE

DRAINAGESWALE

GAS COLLECTION GEOCOMPOSITE

1

VARIES

VEGETATEDTOP SOIL

4 m

.45 m

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PRIMARY REINFORCEMENT

GAS COLLECTION SAND

REINFORCED SOILSLOPE FACE WRAP

STRUCTURAL

FILL

SECONDARY REINFORCEMENT

GEOMEMBRANE

GEOMEMBRANE

DRAINAGESWALE

GAS COLLECTION GEOCOMPOSITE

1

VARIES

VEGETATEDTOP SOIL

4 m

.45 m

STEEP FACE WITH GRASS Geogrid Reinforcement Arrangement

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69 MACCAFERRI

LANDFILL BEHIND REINFORCED-SOIL EMBANKMENT