Post on 13-Apr-2020
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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!!