WIXLIB

DOs and DO NOTs ofSubgrade MaintenanceAustralian Rail TrackCorporation, LTD

Why are we here? ImproveSafety Improve quality of the track structure Reduce re-work Review examples of real life problems Exchange stories and experiences

Today’s Program1. Subgrade Maintenance2. Trench Drain Construction

Presentation Outline SoftTrack Ballast Pockets Drainage Culverts Construction Practices Over Steepened Slopes Riprap Record Keeping

Presentation Outline SoftTrack Ballast Pockets Drainage Culverts Construction Practices Over Steepened Slopes Riprap Record Keeping

Idealized Track SectionSleeperR ailT ieB allastS u b b allastS u b g rad e

Less Than Ideal Track SectionTHIN,CONTAMINATEDBALLAST LAYERNO TOPFORMATIONDEFORMEDCLAYSUBGRADE

Another Less than Ideal EDSUBGRADENO TOPFORMATION

What is “Soft Track”?

What is “Soft Track”?

What is “Soft Track”?

What is “Soft Track”?

What is “Soft Track”?

What is “Soft Track”? Ballastfailure and pumping track Top Formation failure Shallow subgrade failures Rigid layer “mud”pumping Embankment failure Landslides

Contributors to “Soft Track” WaterWeak Subgrade SoilOverstressed SoilFouled Ballast Poor InitialConstructionPoor MaintenancePracticesOver Loaded andOver SteepenedSlopes

Water is a Major Contributorto Soft Track and the key to reducing theoccurrence of soft track is DRAINAGEDRAINAGEDRAINAGE

Presentation Outline SoftTrack Ballast Pockets Drainage Culverts Construction Practices Over Steepened Slopes Riprap Record Keeping

The Ballast Pocket Water trapped in a ballast pocketis a major contributor to many softtrack situations Ballast Pocket

Ballast Pocket Exposed inTrench below TrackBALLASTPOCKETCLAY

Ballast Pockets under each RailHEAVEDCESSDEFORMEDSUBGRADEBALLASTPOCKET

Water Flowing from Ballast PocketBALLASTPOCKETWATER

Ballast Pockets associated withCommon Subgrade Failure ModesDirection ofGround MovementFailure SurfaceUndercutting does not removeor drain the ballast pocketBallast pocketdevelopment.Water trapped indepressions under rail.Bearing failure (withshear displacement).Water saturated ze,minimal minimalsubgradesubgradedeformation.deformation.

Ballast Pockets associated withCommon Subgrade Failure ModesSeepsShallow shearfailure blocksditch.Failure SurfaceSeepsDeepershearfailure.Failure Surface

Presentation Outline SoftTrack Ballast Pockets Drainage Culverts Over Steepened Slopes Construction Practices Riprap Record Keeping

Sources of Water Rainor snow Surface water infiltration Water within the track structure Groundwater

Proper Surface Drainage is probably the least expensive andmost easily implemented measure forpreventing soft track problems orimproving performance of soft trackareas

Indicators of Poor Drainage

Wet Ground near or on theEmbankment

Ponded Water Adjacent to Track

Cattails on Slope above Track

Water Ponded in Ditch andWetlands Plants

Infiltration and Embankment FailureResulting from Poor DrainagePonded WaterCracksTrackPonded illInfiltrationFailure Surface

Cess Failure due in part to PoorSurface DrainageBERM ALONGCESSPONDED WATERCONTRIBUTEDTO FAILURE

Improved Surface DrainageCleanditch,cessprovidedrain, provideCleanadequateadequateslope so slope ch,or cleanadd or addculverts,etc.etc.culverts,Slope shouldercess to drain.Slopeto drain.TrackDo notnotconcentrateconcentrateDoflows.flows.Fill

Surface DrainageDos and Do Not’s DOdivert water away from track DO keep cess drains clean andgraded DO keep cesses clean and sloped todrain DO NOT let water pond DO NOT let water infiltrate theembankment

Subsurface DrainageSystems are effective for draining water from soil draining water from ballast pockets draining water from cracks in theground lowering the groundwater elevation intercepting water flowing toward thetrack

Examples of SubsurfaceDrainage Systems Drainsoriented perpendicular to thetrack Drains oriented parallel to the track Drains in wet areas further awayfrom the track

Trench Drains Perpendicular to Track are discussed in the second half of the course

Shallow Trench Drains InstalledParallel to the TrackLoweredGroundwaterTableTrench drains, depth varies,3-feetminimum.minimum.1 meter

Deep Trench Drain Parallel to TrackWater-loving Plants orSprings on Slope FaceFillGroundwater Elevationin Fill Before InstallingTrench DrainLowered 515-Ft.MetersDeepTrench DrainTrenchDrain(typical)(typical)

Subsurface DrainageDos and Do Nots DOdrain ballast pockets DO construct cutoff drains upgradeof soft track DO NOT construct deep drainswithout the assistance ofexperienced personnel DO NOT get in trenches

Presentation Outline SoftTrack Ballast Pockets Drainage Culverts Over Steepened Slopes Construction Practices Riprap Record Keeping

Culverts are part of the surface drainagesystem

Common Culvert Problems Noculvert installed Culvert too small Spacing between culverts too great Culvert plugged Culvert damaged Drainage toward inlet not properlygraded Culvert discharges onto embankment

Embankment Failure Resulting fromImpounded WaterWater Flow Through Embankment,Decreasing StabilityTrackImpounded WaterFillOriginal Cross-sectionDroppedCess ororFillDropped ShoulderFillPlugged Culvert,Plugged Culvert Inlet,or No Culvert InstalledFailureSurface

Erosion of Embankment Slope byWater Flowing Over the EmbankmentImpounded WaterWater Flow Over or Through TrackStructure Eroding EmbankmentOriginal Cross-sectionPlugged Culvert,Plugged Culvert Inlet,or No Culvert InstalledEroded Embankment

Culvert Issues Maintenance Installation InletProtection and Trash Racks Outlet Erosion Protection

PluggedCulverts

Washoutbecause ofPluggedCulvert

Beaver DamaroundCulvert Inlet

Embankment failure afterbeavers plugged inlets

Culvert Issues Maintenance Installation InletProtection and Trash Racks Outlet Erosion Protection

Culvert Installation when done properly ensures thatthe culvert and embankmentfunction properly

PrepareFoundation andBedding

Trench Safety !Sloping, Benching, andShoring !

Use appropriatebackfill material

Place fill belowpipe haunches

Compact Backfill Material !

Removetemporarysupports aftercompletinginstallation

Additional InstallationConcerns Gradecess drain so that waterflows toward culvert inlet Use low permeability backfill soilaround inlet end of culvert Construct concrete headwall orcutoff wall around inlet

Culvert Issues Maintenance Installation InletProtection and Trash Racks Outlet Erosion Protection

Consider inlet structures, flared inlets,and other protection for inlets

Lined inlet channels and cessdrains are sometimes appropriate

Culvert Inlet Trash Racks are one method to reduce thepotential for culverts and culvertinlets to become plugged withdebris

Horizontal Trash Rack may beeasily Plugged with Debris

Riser Trash Racks over existingHorizontal Trash Racks

Vertical Trash Rack

Overflow Risers / Secondary Inlets

Culvert inlets withtrash racks andoverflow inlets

Culvert Issues Maintenance Installation InletProtection and Trash Racks Outlet Erosion Protection

Erosion Below CulvertOutlets another all too common contributorto embankment failures

Erosion Below Culvert Outlet

OLD, DAMAGEDWOODEN CULVERTErosionbelowCulvertOutlet

Erosion BelowOverflowExtendCulvertsCulverts orProtect Slope

Discharge at Toe of Slope

Line Discharge Channels with Riprap

Use Outlet Structuresif Appropriate

Culvert Dos and Do NotsDO maintain culverts in good condition DO replace culverts that are too small DO properly install culverts DO install inlet structures and trashracks where appropriate DO NOT let culverts or culvert inletsbecome clogged DO NOT discharge culverts onunprotected embankments

Presentation Outline TrackComponents Soft Track Ballast Pockets Drainage and Culverts Construction Practices Over Steepened Slopes Riprap Record Keeping

Poor Construction Practice can create problems that aredifficult and expensive to deal withlater

An Old Side-hill FillRailroad EmbankmentOriginal GroundSurface BeforeRailroad ndcess raising.)Original Embankment SlopeLayer of Brush Buried BelowOriginal Fill, Now RottedBallast PocketUncompacted Soil with OrganicsTopsoil (Left in place duringinitial construction)

The Severity of Embankment Problemsmay Increase Over TimeMain 2Main 1BallastClayey SANDGravelly SANDClayey SAND; WetCinders?Failure SurfaceBottom of Trench

Bridge Fills Embankment stability problemsare frequently associated withtrestles and bridges that have beenreplaced with fills

Prior to placing fill . WEAK MATERIALSHOULD BE REMOVEDPERMITS MAYBE REQUIRED !!!

fill materialsshould becompactedIf compaction is out ofthe question- use quality fill materialor special techniques

An Example of Problems at aTimber Bridge that wasReplaced with Fill

Close up of Bulge in Embankmentand Offset FlumeBULGE INEMBANKMENTAND 2- METEROFFSET IN FLUME

Cracks in EmbankmentCRACKSFLUME

Culvert DamagedNote that struts were never removed

Old Bridge PilesBuried in FillREMOVE PILECAPS

More Old Piles in Fill-Note, piles are leaning as a result of embankment movement

Cross Section through theEmbankmentBallastTiesSandy GRAVELSlickensidesClayey SANDFailure SurfaceCLAY?Bottom of TrenchSandy CLAY

BallastBrown SANDTan SAND/Some BallastBulgeCLAYFailure SurfaceBottom of Trench

Embankment Repair Weak Soil Replaced - Slope FlattenedREPLACE WITHBALLASTEXCAVATEWEAKMATERIALReplacement performed in short segments under the guidance of a geotechnical engineer

Riprap PlacedPERMITS MAY BEREQUIRED !!

Embankment ConstructionDos and Do Nots DOremove unsuitable soils beforeplacing fill DO compact fill materials DO keep slopes as flat as possible DO NOT forget to provide drainage

Presentation Outline TrackComponents Soft Track Ballast Pockets Drainage and Culverts Construction Practices Over Steepened Slopes Riprap Record Keeping

Over Loading and OverSteepening of Slopes two other common causes ofembankment slope failures .

Over Loaded and OverSteepened Slopes Occuras a Result of: Excessiveraising of the track Disposal of material on the slope “Bank Widening” Erosion of the toe of the slope Undercutting of the toe of the slope

Over Loading and OverSteepening of an Existing eepenedCessShoulderFailure SurfaceCaused by Overloading Slope

Over Loading SlopeMATERIALREMOVED FROMDITCH PILED ONCESS.EMBANKMENTCESS WIDENED

Failure of Over Loaded andOver Steepened EmbankmentSOIL AND ROCKPLACED ONSLOPEPOOR SURFACEDRAINAGE ALSOCONTRIBUTED TOTHIS FAILURE

Undercutting Embankment ToeTrackSTEEPENED SLOPEOVERLOADOriginal SlopeFailure SurfaceCaused by Undercuttingof Toe of SlopeToe of slope undercutby railroad personnelor contractor.

Slope Failure Caused byErosion at Toe

Slope OverSteepened byErosion at Toe

Over Steepened andOver Loaded SlopesDos and Do Nots DOprotect slopes from beingeroded or undercut DO NOT dispose of spoil materialon slopes or near the top of slopes DO NOT perform “Bank Widening” DO NOT steepen the slopes ofexisting embankments

Embankment Flattening andButtressing flatter slopes are more stable thansteep slopes .

Embankment Stability Improvedby Flattening the SlopeCompacted Soil Fill (Buttress)Extend Drainthrough New FillCut Benches into Existing Slope- Remove weak or loose soil,topsoil, vegetation, and debris.Drainage Gravel LayerKey into Firm Ground- Remove weak or loose soil,topsoil, vegetation, and debris.Drainage Installed in Existing Embankment

Embankment Stability Improvedby Buttressing the SlopeCompacted Soil Fill (Buttress)Filter Layer(s)Riprap Slope ProtectionFlood Water LevelCut Benches into Existing Slope- Remove weak or loose soil,topsoil, vegetation, and debris.Normal Water LevelDrainage Gravel LayerKey into Firm Ground- Remove weak or loose soil,topsoil, vegetation, and debris.Drainage Installed in Existing EmbankmentLow Water LevelExtend Drainthrough New Fill

Flattened Slope

Slope Repair, Flattening or Buttressingwith Large Rock is Not RecommendedTrackSinkhole Caused by Erosion ofEmbankment Material into VoidsBig RocksEmbankmentVoids (air space)