Design of Roadway Design of Roadway Drainage SystemsDrainage Systems

Using Geocomposite Drainage Using Geocomposite Drainage LayersLayers

by by

Barry R. Christopher, Ph.D., P.E.Barry R. Christopher, Ph.D., P.E.

PAVEMENT DESIGNPAVEMENT DESIGN

TRAFFICTRAFFIC

LIFE-CYCLECOST

ANALYSIS

LIFE-CYCLECOST

ANALYSIS

FAILURE CRITERIA

FAILURE CRITERIA

MINIMUM THICKNESS, etc.

MINIMUM THICKNESS, etc.

ENVIRONMENTENVIRONMENT

STRUCTURAL MODEL

STRUCTURAL MODEL

MATERIALSMATERIALS

CONSTRUCTION COSTS

CONSTRUCTION COSTS

RIDEABILITYRIDEABILITY

STRUCTURAL DESIGN

STRUCTURAL DESIGN

OPTIMUM INVESTMENT LEVELOPTIMUM INVESTMENT LEVEL

RELIABILITY (pavement condition)

PR

ES

EN

T W

OR

TH

OPTIMUM

100 %50 %

TOTAL COST

FUTURE INVESTMENT Maint., Rehab., User, etc.

INITIAL COST

CONSIDERATIONSCONSIDERATIONSIN PAVEMENT DESIGNIN PAVEMENT DESIGN

Continuous & Rapid Deterioration with TimeRepeated & Dynamic LoadingDifferent Load Magnitudes & ConfigurationsTraffic Distribution and GrowthChange Materials Properties &

CharacteristicsDrainageDrainageContamination of Road Materials

FAILURE CRITERIA IN FAILURE CRITERIA IN PAVEMENTSPAVEMENTS

RUTTING

FATIGUE CRACKING

THERMAL CRACKING

REFLECTION CRACKING

CONTAMINATION

DRAINAGE/ MOISTURE

MECHANISTIC-EMPIRICAL FRAMEWORK IN MECHANISTIC-EMPIRICAL FRAMEWORK IN THE 2002 PAVEMENT DESIGN GUIDE.THE 2002 PAVEMENT DESIGN GUIDE.

Temperature

Precipitation

Humidity

Depth to Water Table

Frost Susceptibility

Capillary rise Potential

ENVIRONMENTAL / CLIMATICENVIRONMENTAL / CLIMATIC FACTORSFACTORS

Water in the Pavement Structure

PrimaryCause ofDistress

Standing water in a pavement indicates low permeability and poor drainage Standing water in a pavement indicates low permeability and poor drainage

TireTire

Subgrade Subgrade

DRAINAGEDRAINAGE

LOADED FLEXIBLE LOADED FLEXIBLE PAVEMENTPAVEMENT

Deflection of Aggregate Base

Free Water Wedge

Hydrostatic Pressure

Deflection of Subgrade

Direction of Travel

Under traffic loading, water and base material squirting up through joint in Under traffic loading, water and base material squirting up through joint in PCC pavementPCC pavement

Loaded PCC PavementLoaded PCC Pavement

Free Water Hydrostatic Pressure or Water Jet

Direction of Traffic

Direction of Traffic

Water is Violently Displaced Carrying Suspended Fines

JOINT DETERIORATIONJOINT DETERIORATION

Water in Pavements SummaryWater in Pavements Summary

• Stripping in HMA

• Loss of Subgrade Support

• Reduction of Granular Layer Stiffness

• Erosion of Cement-Treated Base Layers

• Reduction in the Pavement Service Life If Base Is Saturated for Sometime

• Debond between Layers

Three important components for a Three important components for a good pavement designgood pavement design

DrainageDrainage

DrainageDrainage

DrainageDrainage

AASHTO Drainage DefinitionsAASHTO Drainage Definitions

Quality of Drainage

Excellent

Good

Fair

Poor

Very Poor

Water Removed Within*

2 Hours

1 Day

1 Week

1 Month

Water will not Drain

AASHTO Guide for Design of Pavement Structures, 1993

*Based on time to drain*Based on time to drain

Crushed Crushed OutletOutlet

Clogged Clogged OutletOutlet

Time To DrainTime To Drain

For two lane road - Lane width = 24 ft, Slope = 0.01For two lane road - Lane width = 24 ft, Slope = 0.01

BaseBase k k time to draintime to drain QualityQuality

OGB OGB 1000 ft/day 1000 ft/day 2 hrs to drain2 hrs to drain ExcellentExcellent

DGABDGAB 1 ft/day 1 ft/day 1 week1 week FairFair

DGAB DGAB w/ finesw/ fines 0.1 ft/day 0.1 ft/day 1 month1 month PoorPoor

RealityReality no drains no drains does not draindoes not drain Very PoorVery Poor

Geocomposite Drain RequirementsGeocomposite Drain Requirements

Sufficient stiffness to support traffic without significant deformation under dynamic loading

Inflow capacity > infiltration from adjacent layers

Sufficient transmissivity to rapidly drain the pavement section and prevent saturation of the base

Sufficient air voids within geo-composite to provide a capillary break

Drainage Geocomposite - Drainage Geocomposite - Important PropertiesImportant Properties

Transmissivity = 4500 ft2/day (0.005 m2/sec) Estimated Discharge: 30 ft3/day /ft

Creep Resistance under high Loads

Long-term Resistance to Compression

Stability Traffic Loads = Univ. of Illinois Study

Effective Porosity = 0.7

Geotextile Filtration Requirements

Design guidance for a new alternative drainage method Horizontal geocomposite drainage layer tied directly and

continuously into an edge drain system. RoaDrain™ 100-2 by the Tenax Corporation) Current AASHTO and Corps of Engineers pavement design codes

Application Used directly to replace drainable aggregate layers in rigid or flexible

pavement systems, or Enhance the drainage of dense graded aggregate layers often used in

flexible and rigid pavement systems.

Design Manual for Roadway Geocomposite Design Manual for Roadway Geocomposite Underdrain Systems: SCOPEUnderdrain Systems: SCOPE

Factors Affecting The DesignFactors Affecting The Design

Pavement slopes

Aggregate gradation

Porosity and effective porosity

Layer saturation

Permeability

Pavement SlopesPavement Slopes LR

S

SX

SR

AW

A

SxSR

SW LR

( )S S SR x= +2 2 0 5.

LR WSSX

=

1

2 0.5

Tan A SSX

( ) =

Pavement SlopesPavement Slopes

Surface and subsurface Surface and subsurface slopesslopes

Always positive SAlways positive SRR

Recommended slopes:Recommended slopes:0.02 m/m (normal 0.02 m/m (normal

conditions)conditions)0.025 m/m (high rainfall)0.025 m/m (high rainfall)

Surface and subsurface Surface and subsurface slopesslopes

Always positive SAlways positive SRR

Recommended slopes:Recommended slopes:0.02 m/m (normal 0.02 m/m (normal

conditions)conditions)0.025 m/m (high rainfall)0.025 m/m (high rainfall)

t = T x m x 24

Time-to-Drain CalculationTime-to-Drain Calculation

m-factor (days)Time factor

Time to drain (hrs)

Time to drainTime to drain

t = T x m x 24t = T x m x 24

where,where, t = time to drain in t = time to drain in hourshours

T = Time FactorT = Time Factor

m = “m” factorm = “m” factor

Sl = LRSr/HSl = LRSr/H

How to Estimate Time to Drain (t)How to Estimate Time to Drain (t)

Input: S and Sx W, H, k, d, Gsb, WL (for permeable base)

Interim Output: SR, LR, S1 {S1 = (LR x SR)/H} T for a desirable degree of drainage (U) N and Ne

N = [1- {d / (9.81 x Gsb)}] Ne = N x WL

“m” factor: m = (Ne x LR2) / (k x H)

Output: t = T x m x 24

Transmissivity

Time-to-Drain SensitivityTime-to-Drain Sensitivity

Factors affecting time-to-drain:

Effective porosity

Coefficient of permeability

Resultant slope

Resultant length

Permeable base thickness

0 305 610 915 1220

2

4

6

Coefficient of Permeability, m/day

Tim

e to

Dra

in,

hrs

Effect of kEffect of k

LR = 7.6 mH = 0.15 mU = 50%SR = 0.02 m/m

Effect of SEffect of SRR

.02 .04 .060

.2

.4

.6

.8

1

Resultant Slope, m/m

Tim

e to

Dra

in,

hrs

LR = 7.6 mH = 0.15 mU = 50%Ne = 0.25k = 915 m/day

Effect of LEffect of LRR

0 3.6 7.2 10.8 14.4

1

2

Resultant Length, m

Tim

e to

Dra

in,

hrs SR = 0.02 m/m

H = 0.15 mU = 50%Ne = 0.25k = 915 m/day

0 100 200 300

.5

1

1.5

Permeable Base Thickness, mm

Tim

e to

Dra

in,

hrs SR = 0.02 m/m

U = 50%Ne = 0.25 m/mk = 915 m/dayLR = 7.6 m

Effect of ThicknessEffect of Thickness

1

2

3

5

7

0.01 .03 .10 .30 .60

Slo

pe

Fac

tor

(S1)

Time Factor (T50)

T for U = 50% DrainedT for U = 50% Drained

RoaDrainRoaDrainTMTM Time to Drain Time to Drain

Case B - Beneath PavementCase B - Beneath PavementTime to Drain < 10 minTime to Drain < 10 min

Case A - Beneath SubbaseCase A - Beneath Subbase for 15 in subbase with k = 1 ft/dayfor 15 in subbase with k = 1 ft/dayTime to drain ~ 3 hoursTime to drain ~ 3 hours

Wisconsin DOT, Highway 60Wisconsin DOT, Highway 60Wisconsin DOT, Highway 60Wisconsin DOT, Highway 60

GPR SurveyGPR Survey

ConclusionsConclusions The RoaDrainThe RoaDrainTMTM geocomposite drainage layer is an effective geocomposite drainage layer is an effective

alternative for pavement drainage.alternative for pavement drainage. Calculations based on time-to drain approach indicate:Calculations based on time-to drain approach indicate:

adequate infiltration rates to handle significant storm events.adequate infiltration rates to handle significant storm events. < 10 min. to drain the geocomposite layer. < 10 min. to drain the geocomposite layer. < 2 hours hours to drain the road even when placed beneath moderately < 2 hours hours to drain the road even when placed beneath moderately

permeable dense graded aggregate base. permeable dense graded aggregate base. i.e. excellent drainage based on AASHTO 1998 criteria.i.e. excellent drainage based on AASHTO 1998 criteria.

Five case studies in progress with 3 monitored study showing:Five case studies in progress with 3 monitored study showing: Excellent to good drainage following major storm events.Excellent to good drainage following major storm events. Geocomposite drains in subgrade found most effective, especially during Geocomposite drains in subgrade found most effective, especially during

spring thaw.spring thaw. Geocomposite drains facilitated construction and may have improved Geocomposite drains facilitated construction and may have improved

roadway section stiffness. roadway section stiffness. FEM study shows good potential for Strain Energy AbsorptionFEM study shows good potential for Strain Energy Absorption

QUESTIONS ?QUESTIONS ?

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