geosynthetics: can they reduce base thickness? · se strengthening)se strengthening) subgrade &...

GeosyntheticsGeosynthetics: Can: CanGeosyntheticsGeosynthetics: Can: CanBase Thickness?Base Thickness?

AsAsAsAs

n They Reducen They Reducen They Reduce n They Reduce

Richard Reid, Ph.D., P.E.Richard Reid, Ph.D., P.E.ssociate Dean of Engineeringssociate Dean of Engineering

SDSUSDSUssociate Dean of Engineeringssociate Dean of Engineering

Director, SD LTAPDirector, SD LTAP

OverOver

The Answer The Answer DefinitionsDefinitionsSeparation (betweeSeparation (betweeReinforcement (basReinforcement (basReinforcement (basReinforcement (basFiltration (between Filtration (between VariablesVariablesPerformancePerformance

rviewrview

en subgrade & base)en subgrade & base)se strengthening)se strengthening)se strengthening)se strengthening)subgrade & base)subgrade & base)

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The QuThe QuThe QuThe Qu

If I use If I use geosynthetigeosyntheti•• Reduction in base cReduction in base c•• IIncrease in total vencrease in total ve

TheTheTheTheIt DependsIt Depends

uestionuestionuestionuestion

icic x, what will be my:x, what will be my:course? (BCR)course? (BCR)hicle passes? (TBR)hicle passes? (TBR)

e Answere Answere Answere Answer

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DefinDefinDefinDefin

Base Course ReductionBase Course Reduction•• Reduction in base layer tReduction in base layer t

geosyntheticgeosynthetic•• Same number of passesSame number of passes

Traffic Benefit Ratio (TBTraffic Benefit Ratio (TB•• Ratio (for same section tRatio (for same section t((

# of cycles of reinforced sec# of cycles of reinforced sec# of cycles of unreinforced s# of cycles of unreinforced s

nitionsnitionsnitionsnitions

n (BCR)n (BCR)thickness due to presence of thickness due to presence of

s but with less bases but with less baseBR)BR)thickness) of:thickness) of:))ction to achieve a given rut depthction to achieve a given rut depthsection to achieve same rut depthsection to achieve same rut depth

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TBRTBRTBR vsTBR vsTraffic Benefit RatioTraffic Benefit RatioTraffic Benefit RatioTraffic Benefit Ratio

50,000 ESAL’s 100,000 ESAL’s

BCRBCRs. BCRs. BCRBase Course ReductionBase Course ReductionBase Course ReductionBase Course Reduction

50,000 ESAL’s 50,000 ESAL’s

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Types of Types of GeosynGeosynUsed inUsed in

theticsthetics Typically Typically n Roadsn Roads

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DefinDefinDefinDefinnitionsnitionsnitionsnitions

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DefinitioDefinitioDefinitioDefinitio

GeotextilesGeotextiles

ns (ns (con’tcon’t))ns (ns (con tcon t))

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Functions of OuFunctions of Ouur ur GeosyntheticsGeosynthetics

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SeparationSeparation•• Provides separationProvides separation

materialsmaterials•• Prevents interminglPrevents intermingl

i ifi tl diffi ifi tl diffsignificantly differensignificantly differen–– Base course contamBase course contam

All fAll f•• Allows free movemAllows free movemGeotextilesGeotextiles


n between two dissimilar n between two dissimilar

ling of soil layers that possess ling of soil layers that possess t i i di t ib tit i i di t ib tint grain size distributionsnt grain size distributions

minationminationt f t b t lt f t b t lent of water between layersent of water between layers

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SeparSeparSeparSeparrationrationrationration

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ReinforcementReinforcement•• Adds tensile strengthAdds tensile strengthgg•• Embankments over sEmbankments over s•• Construction of steepConstruction of steep•• Construction of steepConstruction of steep•• Reinforcement or stifReinforcement or stif

––GeosyntheticsGeosynthetics have nhave n

GeogridsGeogrids or geotextilor geotextilgg gg


h to soilh to soilsoft soilssoft soilsp slopes & retaining wallsp slopes & retaining wallsp slopes & retaining wallsp slopes & retaining wallsffening of layers?ffening of layers?no structural numberno structural number

ilesilesSDSUSDSU

ReinforcementReinforcementReinforcementReinforcementt or Stiffening?t or Stiffening?t or Stiffening?t or Stiffening?

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Base ImpBase ImpBase ImpBase Imp

Lateral Shear Lateral Shear FlowFlow

•FlowFlow

Lateral Restraint Due to Lateral Restraint Due to FrictionFriction

provementprovementprovementprovement

• Lateral Restraint–– Confinement of the aggregate Confinement of the aggregate Confinement of the aggregate Confinement of the aggregate

base during loadingbase during loading–– Results in increase in STIFFNESS Results in increase in STIFFNESS

of the base materialof the base materialof the base materialof the base material–– Improved/reduced vertical Improved/reduced vertical

stress distribution applied to stress distribution applied to

t b dt b dpavement subgradepavement subgrade

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FiltrationFiltration•• Prevent soil migrationPrevent soil migrationgg•• Prevent soil from migPrevent soil from mig

layerlayerlayerlayer•• Used below ripUsed below rip--rap/arrap/ar

drainage systemsdrainage systemsdrainage systemsdrainage systemsGeotextilesGeotextiles


nngrating into base/drainage grating into base/drainage

rmor materials and in rmor materials and in

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FiltrationFiltrationFiltrationFiltration

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Geosynthetic FunctioGeosynthetic FunctiollFiltrationFiltration

onsons

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When May We RWhen May We RWhen May We RWhen May We R

When subgrades arWhen subgrades armust be added to smust be added to s

educe Thickness?educe Thickness?educe Thickness?educe Thickness?

re soft and additional base re soft and additional base stabilize subgradestabilize subgrade

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When To UseWhen To UseWhen To Use When To Use

When subgrade forWhen subgrade for•• Has a high percentaHas a high percenta•• Is exposed to waterIs exposed to water•• Has the potential toHas the potential to

GeosyntheticsGeosyntheticsGeosyntheticsGeosynthetics

r separation/filtration:r separation/filtration:age of finesage of finesr for extended periods of timer for extended periods of timeo migrate into the baseo migrate into the base

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What Affects BWhat Affects BWhat Affects BWhat Affects B

Subgrade strengthSubgrade strengthAggregate characteAggregate charactegg ggg gDesign requiremenDesign requiremenGeosyntheticGeosynthetic propepropeGeosyntheticGeosynthetic propeprope

Each case is projecEach case is projec

Base ReductionBase ReductionBase ReductionBase Reduction

eristicseristicstt

ertiesertiesertieserties

ct and product uniquect and product unique

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Possible ValuePossible ValueReduction & TrafReduction & TrafReduction & TrafReduction & Traf

Base course reductBase course reduct•• For geotextiles (20For geotextiles (20--•• For For geogridsgeogrids (30(30--5050•• Minimum base thickMinimum base thick

Traffic Benefit RatioTraffic Benefit Ratio•• For geotextiles (1.5For geotextiles (1.5For geotextiles (1.5For geotextiles (1.5•• For For geogridsgeogrids (1.5 (1.5 ––

es of Thickness es of Thickness affic Benefit Ratioaffic Benefit Ratioaffic Benefit Ratio affic Benefit Ratio

tiontion--33%)33%)0%)0%)kness is 6”kness is 6”oo55 –– 10)10)5 5 10)10)

70)70)

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FinalFinalFinal Final

GeosyntheticsGeosynthetics, whe, wheappropriate base mappropriate base mimprove traffic beneimprove traffic beneGeosyntheticsGeosynthetics maymaysections if properly sections if properly •• It will never make aIt will never make a

PointsPointsPointsPoints

en properly installed using en properly installed using materials, will always materials, will always efit ratioefit ratioy allow for reduced base y allow for reduced base

designeddesigneda low quality material better!a low quality material better!q yq y

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QQQuestQuesti ?i ?tions?tions?

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geosynthetics: can they reduce base thickness? · se strengthening)se strengthening) subgrade &...

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