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Behavior of Geosynthetic-Reinforced Earth

Presented by

Kousik Deb

Assistant ProfessorDepartment of Civil Engineering

IIT Kharagpur

Possible Solutions

• Geosynthetic/fiber reinforcement• Metallic strip• Stone columns• Soil-cement columns• Lime columns• Grout columns• Vibro concrete columns• Micro piles

Columnar systems

Problems for Foundations on Weak SoilsProblems for Foundations on Weak Soils

• Experience excessive settlement• Possible bearing capacity failure under load

Placement of Geosynthetic Reinforcement Method of Installation Method of Installation –– Stone ColumnsStone Columns

Typical Applications of Columnar SupportTypical Applications of Columnar Support

Tank foundations Highway embankments

Reinforced earth wallsRailway embankments

OthersOthers

•• Industrial structuresIndustrial structures

•• Bridge approachesBridge approaches

•• RunwaysRunwaysIndividual footings

Combined Use of Geosynthetics and Pile/Columnar System

Widening of existing roads

Subgrade improvement

Retaining walls

Storage tank

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Other Ground Improvement TechniquesOther Ground Improvement Techniques

preloading with or without the use of sand drainspreloading with or without the use of sand drainsremoval and replacementremoval and replacementcompaction by means of explosioncompaction by means of explosiondynamic compaction dynamic compaction groutinggroutingthermal stabilizationthermal stabilizationground freezingground freezingchemical stabilizationchemical stabilization

Major Applications of Major Applications of GeosyntheticsGeosynthetics

Transportation and GeotechnicalTransportation and GeotechnicalGeoenvironmentalGeoenvironmentalHydraulic EngineeringHydraulic EngineeringPrivate DevelopmentPrivate Development

Major Functions of Geosynthetics

ReinforcementReinforcementSeparationSeparationFiltrationFiltrationDrainageDrainageMoisture barrierMoisture barrier

Geosynthetic (GS) MaterialsGeosynthetic (GS) Materials

geotextiles (GT)geotextiles (GT)geogrids (GG)geogrids (GG)geonets (GN)geonets (GN)geomembranes (GM)geomembranes (GM)geosynthetic clay liners (GCL)geosynthetic clay liners (GCL)geopipe (GP)geopipe (GP)geofoam (GF)geofoam (GF)geocomposites (G C)geocomposites (G C)

Geotextiles (GT)Geotextiles (GT)

majority are made from majority are made from polypropylenepolypropylene, polyester, , polyester, polyethylenes and polyamides polyethylenes and polyamides fibersfibersstandard textile manufacturingstandard textile manufacturingwovenwovennonwoven nonwoven very versatile in their primary very versatile in their primary functionfunction

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GEOPIPE GEOFOAM

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Function vs. Geosynthetic TypeFunction vs. Geosynthetic Type

√√√√√√√√√√geocompositegeocomposite√√geofoamgeofoam

√√geopipegeopipe

√√geosynthetic geosynthetic clay linerclay liner

√√geomembranegeomembrane√√geonetgeonet

√√geogridgeogrid√√√√√√√√geotextilegeotextile

ContainmentContainmentDrainageDrainageFiltrationFiltrationReinforcementReinforcementSeparationSeparationType of Type of GeosyntheticGeosynthetic

Design MethodsDesign Methods

(a)(a) ““CostCost””--based on experience/availabilitybased on experience/availability(b)(b) ““SpecificationSpecification”” –– for common applicationsfor common applications(c)(c) ““FunctionFunction”” –– for specialty, critical and/or for specialty, critical and/or

permanent applicationspermanent applications

Application AreasApplication Areas

Transportation/GeotechnicalTransportation/GeotechnicalGeoenvironmentalGeoenvironmentalHydraulic Systems Hydraulic Systems Private DevelopmentPrivate Development

Transportation and Transportation and Geotechnical ApplicationsGeotechnical Applications

GTs as filtersGTs as filtersGTs and GGs as wall reinforcementGTs and GGs as wall reinforcementGTs and GGs as slope reinforcementGTs and GGs as slope reinforcementGC Wick Drains (also called GC Wick Drains (also called PVDsPVDs))GC Erosion Control SystemsGC Erosion Control Systems

Geotextile FiltrationGeotextile Filtration

GT is acting as a filter GT is acting as a filter notnot as a drainas a drainthree design requirements:three design requirements:

1.1. adequate flowadequate flow2.2. proper soil retentionproper soil retention3.3. longlong--term flow equilibriumterm flow equilibrium

many applications, e.g.,many applications, e.g.,behind retaining wallsbehind retaining wallsunder erosion control systemsunder erosion control systemsaround pavement around pavement underdrainsunderdrains (follows)(follows)

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PavementStonebase

Soil subgrade

Topsoil

450 mm

400 mm

300 mm

Crushed stone/perforated pipe

GT

(GT Filter in Excavated Trench) (Crushed Stone & Perforated Pipe)

Geotextile FiltrationGeotextile FiltrationWall Reinforcement Design ConceptsWall Reinforcement Design Concepts

internal design results in:internal design results in:•• spacing of GT or GGspacing of GT or GG•• length of GT or GGlength of GT or GG

external design used to assess:external design used to assess:•• overturning stabilityoverturning stability•• sliding stabilitysliding stability•• bearing capacitybearing capacity

reduction factors on reinforcementreduction factors on reinforcement•• put on laboratory values for allowable strengthput on laboratory values for allowable strength

factorfactor--ofof--safetysafety•• on each design aspect to resist the on each design aspect to resist the ““unknownunknown””

Various Types of Reinforced Retaining WallVarious Types of Reinforced Retaining Wall

Elements of a GT or GG Wall DesignElements of a GT or GG Wall Design

L0L

H

zLELR

sv45+φ/2

P2(live loads)P1

DSurcharge

+σhs

Soil pressure

+σhq

Surcharge pressure

=σht

Live load pressure

σh

Total lateral pressure

(With Concrete Facing) (Green Wall with Vegetated Facing)

Reinforcement for Soil SlopesReinforcement for Soil Slopes

most soil slopes become unstable steeper than most soil slopes become unstable steeper than 2(H)2(H)--toto--1(V) (26.51(V) (26.5°°))use GT or GG reinforcement to increase either use GT or GG reinforcement to increase either the slope angle or heightthe slope angle or heightessentially no limit, except for erosionessentially no limit, except for erosionvarious placement patterns are possiblevarious placement patterns are possible

Placement patterns for reinforcementPlacement patterns for reinforcement

(a) Even spaced-even length (b) Uneven spaced-even length

(c) Even spaced-even lengthwith short facing layers

(d) Even spaced-uneven lengthwith short facing layers

(One that Failed)! (With Reinforcement-Steep & Stable)

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Geocomposite Wick DrainsGeocomposite Wick Drainsalso called prefabricated vertical drains (also called prefabricated vertical drains (PVDsPVDs))used for rapid consolidation of saturated fine grained used for rapid consolidation of saturated fine grained soilssoilsconsists of a drainage core with a GT filter/separator consists of a drainage core with a GT filter/separator wrapped completely around itwrapped completely around ittypically 100 mm wide, by 2 to 10 mm thick, by 100 m typically 100 mm wide, by 2 to 10 mm thick, by 100 m long (in roll or coil form)long (in roll or coil form)

(Driving Wick Drains) (Ready for Surcharge Fill)

GeocompositeGeocomposite Erosion Control SystemsErosion Control Systems

huge array of productshuge array of productsslope protectionslope protectionchannel protection channel protection –– increase shear stressincrease shear stress

Nature of Waste ProblemNature of Waste Problem

moisture within and precipitation on the waste moisture within and precipitation on the waste generates leachategenerates leachateleachate takes the characteristics of the wasteleachate takes the characteristics of the wastethus leachate is very variable and is sitethus leachate is very variable and is site--specificspecificflows gravitationally downwardflows gravitationally downwardenters groundwater unless a suitable barrier layer enters groundwater unless a suitable barrier layer and collection system is providedand collection system is provided

Double Liner SystemDouble Liner System(with leak detection layer)(with leak detection layer)

GT

GG

GN

GCLGM perforated pipe

(Geonet Leak Detection)

(Nine Layers of Geosynthetics)

Final Cover SystemFinal Cover System

GP or GC

GT

GG

Cover Soil

GCL

GM

GC or GN

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Possible Geosynthetic LayersPossible Geosynthetic Layersin a Waste Containment Systemin a Waste Containment System

in Final Cover - 7

in Waste Itself - 2

in Base Liner - 9

18 Layers!

(Sequential Placement of GSs)

(Seven Layers of Geosynthetics)

Hydraulic Engineering ApplicationsHydraulic Engineering Applications

Waterproofing of DamsWaterproofing of DamsWaterproofing of CanalsWaterproofing of CanalsReservoir LinersReservoir LinersTunnel Waterproofing & RehabilitationTunnel Waterproofing & RehabilitationPipe Rehabilitation & RemediationPipe Rehabilitation & Remediation

Waterproofing of DamsWaterproofing of Dams

masonry, concrete, earth and RCC damsmasonry, concrete, earth and RCC damsGM is not a structural element, its GM is not a structural element, its waterproofingwaterproofingmany dams over 50many dams over 50--years old often have years old often have leakage; sometimes excessive leakageleakage; sometimes excessive leakage

(Concrete Dam Leaking!)

(Completed Concrete Dam Lining) (Lined Earth Dam: Before Rip-Rap)

(Lining aConcrete Dam)

Waterproofing of CanalsWaterproofing of Canals

conveyance of all liquids; however, water is the most conveyance of all liquids; however, water is the most commoncommondistances and quantities vary greatlydistances and quantities vary greatlyfundamental issue is leakage (i.e., how much, if any, is fundamental issue is leakage (i.e., how much, if any, is allowable)allowable)some type of liner (GM or GCL) is necessarysome type of liner (GM or GCL) is necessary

(Lining a Canal: Before Soil Covering) (GCL Lining of a Canal)

(GM Canal 18 years after GM Lined)

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Reservoir LinersReservoir Liners

potable waterpotable waterindustrial watersindustrial watersprocess waste watersprocess waste waterssewage sludgesewage sludgeindustrial sludgeindustrial sludgeagricultural wastesagricultural wasteshazardous liquidshazardous liquids

used to contain all types of liquids

Common CharacteristicsCommon Characteristics

generally shallow liquid depthsgenerally shallow liquid depthstypically 2 to 7 mtypically 2 to 7 mside slopes from 4(H)side slopes from 4(H)--toto--1(V) to 1(H)1(V) to 1(H)--toto--1(V), 1(V), i.e., i.e., ββ = 14= 14°° to 45to 45°°both exposed and coveredboth exposed and coveredexposed exposed –– GM durability issueGM durability issuecovered covered –– soil stability issuesoil stability issue

(Lined Potable Water Reservoir)

(Huge GM Bag Transporting Potable Water)

Private Development ApplicationsPrivate Development Applications

various dwellingsvarious dwellingsindustrial buildingsindustrial buildingsstorage areasstorage areasparks and parks and playgroundsplaygroundspools and lakespools and lakes

sport fieldssport fieldsgolf coursesgolf coursesairfieldsairfieldsagricultureagricultureaquacultureaquacultureliquid transportationliquid transportation

Selected Areas of Focus

New Tunnel WaterproofingNew Tunnel Waterproofing

many old tunnels without GMs are leakingmany old tunnels without GMs are leakingkey is to use a GT and GM behind the permanent key is to use a GT and GM behind the permanent concrete surfacingconcrete surfacingin turn, this requires a GP drainage systemin turn, this requires a GP drainage system

Pools, Ponds and LakesPools, Ponds and Lakes

sites vary from smallsites vary from small--toto--hugehugeusually access is limitedusually access is limitedliners required for leakage controlliners required for leakage controlcovers sometimes required for covers sometimes required for contamination control and for safetycontamination control and for safety

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Soil-Geosynthetics Interaction

• Confinement Effect• String Effect

Design of Geosynthetic-Reinforced Earth

Failure above top reinforcement layeru > 0.5B

Failure between reinforcement layersh > 0.5B

Failure on a two-layer soil system

Failure within reinforced zone

Types of Failure of Reinforced Earth under Footing Load

Sharma et. al., 2009Improvement in Settlement and BearingDas et. al., 1998

Optimum Thickness of Sand Bed

Optimum Width of Geosynthetic LayerLee et. al., 1999

Failures of Reinforced Embankment

Bearing

Rotational

Internal Spreading

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Reinforced Retaining WallReinforced Retaining Wall

Types of FailureCai and Bathurst, 1996

Design of GeosyntheticDesign of Geosynthetic--Reinforced Wall Reinforced Wall

L0L

H

zLELR

sv45+φ/2

P2(live loads)P1

DSurcharge

+σhs

Soil pressure

+σhq

Surcharge pressure

=σht

Live load pressure

σh

Total lateral pressure

Internal Stability:Step 1Determine the active pressure distribution (σa) on the wallσa = Ka σv = Ka γ zWhere Ka = Rankine earth oressure coefficient = tan2 (45◦- φ/2)

Step 2Select a geotextile that has an allowable strength of σg

Step 3Step 3Determine the vertical spacing of the layer at any depth zDetermine the vertical spacing of the layer at any depth z

SSv = = σg/(Ka γ z FS)Where FS is the factor safety. The magnitude of FS is generally 1.3 to 1.5

Step 4Determine the length of each layer of geotextileL = LR + LE

LR = (H –z)/tan(45◦+ φ/2)andLE = (SSvσa FS)/(2 σv tan φF) ≥ 1mWhere φF = 0.67 φ

Step 5 Determine the lap length, L0 = (SSvσa FS)/(4 σv tan φF)The minimum lap length should be 1m

Design ExampleA geotextile-reinforced retaining wall 6 m high. For the backfill, γ = 19 KN/m3 and φ = 36 ◦. For the Geotextile, σg = 16 KN/m.

Ka = tan2 (45◦- 36 ◦/2) = 0.26

At 2 m depth

SSv = = σg/(Ka γ z FS)= 16/(0.26 x 19 x 2 x 1.5) = 1.08 m

At 4 m depthSSv = = 16/(0.26 x 19 x 4 x 1.5) = 0.54 m

At 6 m depthSSv = = 16/(0.26 x 19 x 6 x 1.5) = 0.36 m

So, use SSv = 0.5 m for z = 0 to 4 m and SSv = 0.33 for z > 4m

Determination of L

L = (H –z)/tan(45◦+ φ/2) + (SSv σa FS)/(2 σv tan φF) = 0.51 (H –z) + 0.435 SSv

At z = 0.5, L = (2.8 + 1) = 3.80 mAt z = 1.0m, L = (2.55 + 1) = 3.55 mAt z = 1.5m, L = (2.3 + 1) = 3.3 mAt z = 2.0m, L = (2.0 + 1) = 3.0 mAt z = 2.5m, L = (1.8 + 1) = 2.8 mAt z = 3.0m, L = (1.5 + 1) = 2.5 mAt z = 3.5m, L = (1.3 + 1) = 2.3 mAt z = 4.0m, L = (1.0 + 1) = 2.0 mAt z = 4.33m, L = (0.85 + 1) = 1.85 mAt z = 4.67m, L = (0.68 + 1) = 1.68 mAt z = 5.0m, L = (0.51 + 1) = 1.51 mAt z = 5.33m, L = (0.34 + 1) = 1.34 mAt z = 5.67m, L = (0.17 + 1) = 1.17 mAt z = 6.0m, L = (0 + 1) = 1.0 m

Determination of L0

L0 = (SSvσa FS)/(4 σv tan φF)

= 0.218 SSv= 0.218 x 0.5 = 0.1 m < 1 m

Take L0 = 1 m

L = 4 m

L = 3 m

L = 2 m

External Stability:

(i) Check for overturning F.S > 3

(ii) Check for SlidingF. S > 3

(i) Check for bearing capacityF.S > 3 to 5

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• The Reinforced Earth walls were designed for a groundacceleration of 0.10 g.

• This resulted in increase in the amount of reinforcing strips compared to static design.

• The actual ground acceleration was measured at 0.4 g.

Izmit Earthquake, Turkey, 1999

Performance of Reinforced Retaining Wall under Seismic Condition

Bridge has been collapsed

Nimbalkar et. al., 2006

Forces acting on single horizontal elemental slice containing reinforcement

Cai and Bathurst, 1996

Effect of Earthquake loading on Factor of Safety

Choudhury et. al., 2008

Effect of Earthquake loading on Required reinforcement Length

At present, the available codes for seismic design of reinforced soil wall systems (e.g., FHWA 1996, AASHTO 1998

SummarySummary

Geosynthetics are bona fide engineering materialsGeosynthetics are bona fide engineering materialsTest methods and designs are available Test methods and designs are available Basic advantage of geosynthetics is quality control Basic advantage of geosynthetics is quality control of factory manufactured productsof factory manufactured productsField performance has been excellentField performance has been excellentGeosynthetics potential is Geosynthetics potential is awesomeawesome!!