SESSION 4 Drainage Design Considerations. Objectives Identify types of subsurface drainage ...

SESSION 4SESSION 4SESSION 4SESSION 4

Drainage Design Drainage Design ConsiderationsConsiderations

Drainage Design Drainage Design ConsiderationsConsiderations

ObjectivesObjectives

Identify types of subsurface drainageIdentify types of subsurface drainage

Determine need for subsurface Determine need for subsurface drainagedrainage

Recognize importance of maintenanceRecognize importance of maintenance

Identify surface drainage design Identify surface drainage design factorsfactors

IntroductionIntroduction

Moisture is a major cause of distressMoisture is a major cause of distress

Drainage long recognized as key Drainage long recognized as key design considerationdesign consideration

Focus on drainage of surface Focus on drainage of surface infiltration waterinfiltration water

Effect of DrainageEffect of Drainage

Moisture-Related Moisture-Related DistressesDistresses

Moisture-Related Moisture-Related DistressesDistresses

Moisture-Related Moisture-Related DistressesDistresses

Moisture-Related Moisture-Related DistressesDistresses

Approaches to Approaches to Drainage ProblemsDrainage Problems

Seal the pavementSeal the pavement

Use moisture-insensitive materialsUse moisture-insensitive materials

Install subsurface drainageInstall subsurface drainage

Types of Subsurface Types of Subsurface DrainageDrainage

Daylighted basesDaylighted bases

Longitudinal edge drain systemLongitudinal edge drain system

Drainable pavement systemDrainable pavement system

DaylightedDaylighted

Subgrade

PCC Slab

Agg. Base

Shoulder

Aggregate Base CarriedOut to Ditchline

Shoulder

Aggregate Base CarriedOut to Ditchline

Traffic LaneTraffic Lane

Longitudinal Edge Longitudinal Edge Drain SystemDrain System

SlopeSlope Slope

Inner Shoulder Traveled Way Outer Shoulder

TPM

FilterFabric

Base (LCB, ACB)

Filter Fabric, High Side ofTangents and Superelevations

PCC PCCPPCCP PCC

California California DesignDesign

Example Drainable Example Drainable Pavement SystemPavement System

AC Shoulder

GeotextileAggregate Separator Layer Permeable

Base

Geotextile

AC Shoulder

PCC Mainline

Components of a Components of a Drainable Pavement Drainable Pavement SystemSystem Permeable basePermeable base

Separator layerSeparator layer

Longitudinal collector pipeLongitudinal collector pipe

Permeable BasePermeable Base

Permeability of 300 to Permeability of 300 to 3,000 m/day (1,000 to 3,000 m/day (1,000 to 10,000 ft/day)10,000 ft/day)

100 to150 mm (4 to 6 100 to150 mm (4 to 6 in) thickin) thick

Treated or untreatedTreated or untreated

Separator LayerSeparator Layer

Prevent intrusion of fines into Prevent intrusion of fines into permeable basepermeable base

Dense-graded aggregateDense-graded aggregate

GeotextileGeotextile

Longitudinal Collector Longitudinal Collector PipePipe Collects water and outlets to ditchesCollects water and outlets to ditches

Typically 100 to 150 mm (4 to 6 in) Typically 100 to 150 mm (4 to 6 in) corrugated plastic pipecorrugated plastic pipe

Outlet spacing 76 to 150 m (250 to Outlet spacing 76 to 150 m (250 to 500 ft)500 ft)

Design and Analysis of Design and Analysis of Drainage SystemsDrainage Systems DefineDefine

Material propertiesMaterial properties Roadway/pavement geometricsRoadway/pavement geometrics Climatic dataClimatic data

Determine inflow/outflow characteristicsDetermine inflow/outflow characteristics

Determine drainage requirementsDetermine drainage requirements

Consideration of Consideration of Drainage in Slab Drainage in Slab Thickness DesignThickness Design

AASHTO Drainage CoefficientAASHTO Drainage Coefficient

Drainage , Thickness Drainage , Thickness

Reduction in properties of paving Reduction in properties of paving materialsmaterials

Determining Need for Determining Need for Subsurface DrainageSubsurface Drainage Available free moistureAvailable free moisture

Material propertiesMaterial properties

Cross sectional designCross sectional design

Subgrade drainabilitySubgrade drainability

Traffic levelsTraffic levels

< 3.0 None

3.0 - 6.0 None/EDS None None None

> 6.0 EDS/DPS

NCHRP 1-32NCHRP 1-32Drainage GuidelinesDrainage Guidelines

EDS = Longitudinal Edge Drain SystemDPS = Drainable Pavement System

WET CLIMATE DRY CLIMATE ESALs, Weak Strong Weak Strong millions Subgrade Subgrade Subgrade Subgrade

Inclusion ofInclusion ofSubsurface DrainageSubsurface Drainage Local experienceLocal experience

Past performancePast performance

Cost effectivenessCost effectiveness

Construction and maintenance Construction and maintenance practicespractices

Maintenance of Maintenance of Drainage InstallationsDrainage Installations Ensures functionality of drainage systemEnsures functionality of drainage system Often a “forgotten” maintenance itemOften a “forgotten” maintenance item Activities include:Activities include:

Reference markersReference markers Cleaning outletsCleaning outlets Flushing/rodding edge drainsFlushing/rodding edge drains Cleaning/reestablishing ditchesCleaning/reestablishing ditches Periodic video inspectionPeriodic video inspection

Video Inspection of Video Inspection of Edge DrainsEdge Drains

Crushed Pipe and Silt Crushed Pipe and Silt BuildupBuildup

Unwanted Unwanted InhabitantsInhabitants

Surface Drainage Surface Drainage ConsiderationsConsiderations Pavement cross slope (tangent section)Pavement cross slope (tangent section)

2% recommended2% recommended Shoulder cross slopeShoulder cross slope

3% recommended3% recommended DitchesDitches

Width: 0.9 to 1.2 m (3 to 4 ft)Width: 0.9 to 1.2 m (3 to 4 ft) Depth: 1.2 m (4 ft) beneath pavement Depth: 1.2 m (4 ft) beneath pavement

Grade: 1%Grade: 1%

SummarySummary

Moisture-related distressesMoisture-related distresses

Subsurface drainage typesSubsurface drainage types

Determining need for subsurface Determining need for subsurface drainagedrainage

Maintenance considerationsMaintenance considerations

Surface drainage considerationsSurface drainage considerations