DOs and DO NOTs of Subgrade Maintenance Australian Rail ... · DOs and DO NOTs of Subgrade Maintenance Australian Rail Track Corporation, LTD. Why are we here? Improve Safety Improve

DOsDOs and DOand DO NOTsNOTs ofofSubgrade MaintenanceSubgrade Maintenance

Australian Rail TrackCorporation, LTD

Why are we here?Why are we here?

Improve Safety Improve quality of the track structureReduce re-workReview examples of real life problems Exchange stories and experiences

1. Subgrade Maintenance

2. Trench Drain Construction

Today’s Program

Presentation OutlinePresentation Outline

Soft TrackBallast PocketsDrainageCulvertsConstruction PracticesOver Steepened SlopesRiprapRecord Keeping

Soft Track Ballast PocketsDrainageCulvertsConstruction PracticesOver Steepened SlopesRiprapRecord Keeping


Idealized Track SectionIdealized Track Section

RailBallast

Tie

Subgrade

Subballast

Sleeper

Less Than Ideal Track SectionLess Than Ideal Track SectionTHIN,

CONTAMINATEDBALLAST LAYER

NO TOPFORMATION

DEFORMEDCLAY

SUBGRADE

Another Less than Ideal TrackAnother Less than Ideal TrackSectionSection

CONTAMINATEDBALLAST

BALLASTPOCKET

NO TOPFORMATION

DEFORMEDSUBGRADE

What isWhat is ““Soft TrackSoft Track””??






Ballast failure and pumping track Top Formation failure Shallow subgrade failuresRigid layer “mud”pumping Embankment failure Landslides

Contributors toContributors to ““Soft TrackSoft Track””

Water Weak Subgrade Soil Overstressed Soil Fouled Ballast

Poor InitialConstruction

Poor MaintenancePractices

Over Loaded andOver SteepenedSlopes

Water is a Major ContributorWater is a Major Contributorto Soft Trackto Soft Track

… and the key to reducing theoccurrence of soft track is ……

DRAINAGE

DRAINAGE

DRAINAGE

Soft TrackBallast PocketsDrainageCulvertsConstruction PracticesOver Steepened SlopesRiprapRecord Keeping


The Ballast PocketThe Ballast Pocket

… Water trapped in a ballast pocketis a major contributor to many soft

track situations …

Ballast Pocket

Ballast Pocket Exposed inBallast Pocket Exposed inTrench below TrackTrench below Track

CLAY

BALLASTPOCKET

Ballast Pockets under each RailBallast Pockets under each Rail

HEAVEDCESS

BALLASTPOCKET

DEFORMEDSUBGRADE

Water Flowing from Ballast PocketWater Flowing from Ballast Pocket

BALLASTPOCKET

WATER

Ballast Pockets associated withBallast Pockets associated withCommon Subgrade Failure ModesCommon Subgrade Failure Modes

Ballast pocketdevelopment.Water trapped indepressions under rail.

Bearing failure (withshear displacement).Water saturated trackstructure.

Subballast squeeze,minimal subgradedeformation.

Direction ofGround Movement

Failure Surface

Undercutting does not removeor drain the ballast pocket

Top Formationsqueeze, minimalsubgrade deformation.

Ballast Pockets associated withBallast Pockets associated withCommon Subgrade Failure ModesCommon Subgrade Failure Modes

Shallow shearfailure blocksditch.

Failure Surface

Seeps

Deepershearfailure.

Failure Surface

Seeps

Soft Track Ballast PocketsDrainageCulvertsOver Steepened SlopesConstruction PracticesRiprapRecord Keeping


Sources of WaterSources of Water

Rain or snow Surface water infiltrationWater within the track structureGroundwater

Proper Surface DrainageProper Surface Drainage

… is probably the least expensive andmost easily implemented measure for

preventing soft track problems orimproving performance of soft track

areas …

Indicators of Poor DrainageIndicators of Poor Drainage

Wet Ground near or on theWet Ground near or on theEmbankmentEmbankment

Ponded Water Adjacent to TrackPonded Water Adjacent to Track

Cattails on Slope above TrackCattails on Slope above Track

Water Ponded in Ditch andWater Ponded in Ditch andWetlands PlantsWetlands Plants

Infiltration and Embankment FailureInfiltration and Embankment FailureResulting from Poor DrainageResulting from Poor Drainage

Track

CracksPonded Water

Ponded Water

Berm or High Shoulder

Infiltration

Failure Surface

InfiltrationFill

Berm or High Cess

Cess Failure due in part to PoorCess Failure due in part to PoorSurface DrainageSurface Drainage

BERM ALONGCESS

PONDED WATERCONTRIBUTED

TO FAILURE

Improved Surface DrainageImproved Surface Drainage

Track Slope shoulder to drain.Do not concentrate flows.

Fill

Clean ditch, provide adequate slope sowater flows along ditch, clean or addculverts, etc.

Clean cess drain, provide adequate slope sowater flows along cess drain, clean or addculverts, etc.

Slope cess to drain.Do not concentrateflows.

Surface DrainageSurface DrainageDos and DoDos and Do NotNot’’ss

DO divert water away from trackDO keep cess drains clean and

gradedDO keep cesses clean and sloped to

drainDO NOT let water pondDO NOT let water infiltrate the

embankment

Subsurface DrainageSubsurface DrainageSystemsSystems

… are effective fordraining water from soildraining water from ballast pocketsdraining water from cracks in the

groundlowering the groundwater elevationintercepting water flowing toward the

track

Examples of SubsurfaceExamples of SubsurfaceDrainage SystemsDrainage Systems

Drains oriented perpendicular to thetrack

Drains oriented parallel to the trackDrains in wet areas further away

from the track

Trench Drains Perpendicular to TrackTrench Drains Perpendicular to Track

… are discussed in the second half of the course

Shallow Trench Drains InstalledShallow Trench Drains InstalledParallel to the TrackParallel to the Track

Trench drains, depth varies,3-feet minimum.

LoweredGroundwaterTable

1 meter minimum.

Deep Trench Drain Parallel to TrackDeep Trench Drain Parallel to Track

Water-loving Plants orSprings on Slope Face

Fill

10 to 15-Ft. DeepTrench Drain (typical)

Groundwater Elevationin Fill Before InstallingTrench Drain

LoweredGroundwater

Table

Lowered GroundwaterTable

3 to 5 Meters DeepTrench Drain(typical)

Subsurface DrainageSubsurface DrainageDos and DoDos and Do NotsNots

DO drain ballast pocketsDO construct cutoff drains upgrade

of soft trackDO NOT construct deep drains

without the assistance ofexperienced personnel

DO NOT get in trenches

Soft Track Ballast PocketsDrainageCulvertsOver Steepened SlopesConstruction PracticesRiprapRecord Keeping


CulvertsCulverts

… are part of the surface drainagesystem …

Common Culvert ProblemsCommon Culvert Problems

No culvert installedCulvert too small Spacing between culverts too greatCulvert pluggedCulvert damagedDrainage toward inlet not properly

gradedCulvert discharges onto embankment

Embankment Failure Resulting fromEmbankment Failure Resulting fromImpounded WaterImpounded Water

Track Water Flow Through Embankment,Decreasing StabilityImpounded Water

Original Cross-sectionFill

Plugged Culvert,Plugged Culvert Inlet,

or No Culvert Installed

Dropped Shoulder or Fill

FailureSurface

Dropped Cess or Fill

Erosion of Embankment Slope byErosion of Embankment Slope byWater Flowing Over the EmbankmentWater Flowing Over the Embankment

Water Flow Over or Through TrackStructure Eroding EmbankmentImpounded Water

Original Cross-section

Plugged Culvert,Plugged Culvert Inlet,

or No Culvert InstalledEroded Embankment

Culvert IssuesCulvert Issues

Maintenance Installation Inlet Protection and Trash RacksOutlet Erosion Protection

PluggedPluggedCulvertsCulverts

WashoutWashoutbecause ofbecause of

PluggedPluggedCulvertCulvert

Beaver DamBeaver Damaroundaround

Culvert InletCulvert Inlet

Embankment failure afterEmbankment failure afterbeavers plugged inletsbeavers plugged inlets



Culvert InstallationCulvert Installation

… when done properly ensures thatthe culvert and embankment

function properly …

PreparePrepareFoundation andFoundation and

BeddingBedding

Trench Safety !

Sloping, Benching, andShoring !

Use appropriateUse appropriatebackfillbackfill materialmaterial

Place fill belowPlace fill belowpipe haunchespipe haunches

Compact Backfill Material !Compact Backfill Material !

RemoveRemovetemporarytemporary

supports aftersupports aftercompletingcompletinginstallationinstallation

Additional InstallationAdditional InstallationConcernsConcerns

Grade cess drain so that waterflows toward culvert inlet

Use low permeability backfill soilaround inlet end of culvert

Construct concrete headwall orcutoff wall around inlet



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

Lined inlet channels and cessLined inlet channels and cessdrains are sometimes appropriatedrains are sometimes appropriate

Culvert Inlet Trash RacksCulvert Inlet Trash Racks

… are one method to reduce thepotential for culverts and culvert

inlets to become plugged withdebris …

Horizontal Trash Rack may beHorizontal Trash Rack may beeasily Plugged with Debriseasily Plugged with Debris

Riser Trash Racks over existingRiser Trash Racks over existingHorizontal Trash RacksHorizontal Trash Racks

Vertical Trash RackVertical Trash Rack

Overflow Risers / Secondary InletsOverflow Risers / Secondary Inlets

Culvert inlets withCulvert inlets withtrash racks andtrash racks andoverflow inletsoverflow inlets



Erosion Below CulvertErosion Below CulvertOutletsOutlets

… another all too common contributorto embankment failures …

Erosion Below Culvert OutletErosion Below Culvert Outlet

ErosionErosionbelowbelow

CulvertCulvertOutletOutlet

OLD, DAMAGEDWOODEN CULVERT

Erosion BelowErosion BelowOverflowOverflowCulvertsCulvertsExtendExtend

Culverts orCulverts orProtect SlopeProtect Slope

Discharge at Toe of SlopeDischarge at Toe of Slope

Line Discharge Channels with RiprapLine Discharge Channels with Riprap

Use Outlet StructuresUse Outlet Structuresif Appropriateif Appropriate

Culvert Dos and DoCulvert Dos and Do NotsNots

DO maintain culverts in good condition DO replace culverts that are too small DO properly install culverts DO install inlet structures and trash

racks where appropriate DO NOT let culverts or culvert inlets

become clogged DO NOT discharge culverts on

unprotected embankments

Track Components Soft Track Ballast PocketsDrainage and CulvertsConstruction PracticesOver Steepened SlopesRiprapRecord Keeping


Poor Construction PracticePoor Construction Practice

… can create problems that aredifficult and expensive to deal with

later …

An Old SideAn Old Side--hill Fillhill FillRailroad EmbankmentRailroad Embankment

Topsoil (Left in place duringinitial construction)

Track

Layer of Brush Buried BelowOriginal Fill, Now Rotted

Original Embankment Slope

Current Embankment Slope(Steepened and shoulder widenedto facilitate track raising.)

Original GroundSurface BeforeRailroad Construction

Ballast Pocket

Uncompacted Soil with Organics

Current Embankment Slope(Steepened and cess widenedto facilitate track raising.)

The Severity of Embankment ProblemsThe Severity of Embankment Problemsmay Increase Over Timemay Increase Over Time

Main 1

Failure Surface Bottom of Trench

Main 2

?

Clayey SAND

Gravelly SAND

Clayey SAND; Wet

Cinders

Ballast

Bridge FillsBridge Fills

… Embankment stability problemsare frequently associated with

trestles and bridges that have beenreplaced with fills …

… WEAK MATERIALSHOULD BE REMOVED

Prior to placing fill ...Prior to placing fill ...

PERMITS MAYBE REQUIRED !!!

…… fill materialsfill materialsshould beshould be

compactedcompacted

If compaction is out ofIf compaction is out ofthe questionthe question

-- use quality fill materialuse quality fill materialor special techniquesor special techniques

An Example of Problems at aTimber Bridge that was

Replaced with Fill

Close up of Bulge in EmbankmentClose up of Bulge in Embankmentand Offset Flumeand Offset Flume

BULGE INEMBANKMENTAND 2- METER

OFFSET IN FLUME

Cracks in EmbankmentCracks in Embankment

CRACKS

FLUME

Culvert DamagedCulvert Damaged

Note that struts were never removed

Old Bridge PilesOld Bridge PilesBuried in FillBuried in Fill

REMOVE PILECAPS

More Old Piles in FillMore Old Piles in Fill

-Note, piles are leaning as a result of embankment movement

Cross Section through theCross Section through theEmbankmentEmbankment

Bottom of Trench

Ties

Ballast

Sandy CLAY

CLAYFailure Surface

Clayey SANDSlickensides

Sandy GRAVEL

? ?

Bulge

Bottom of Trench

CLAY

Tan SAND/Some Ballast

Ballast

Brown SAND

Failure Surface

Embankment RepairEmbankment Repair --Weak Soil ReplacedWeak Soil Replaced -- Slope FlattenedSlope Flattened

EXCAVATEWEAK

MATERIAL

REPLACE WITHBALLAST

Replacement performed in short segments -under the guidance of a geotechnical engineer

Riprap PlacedRiprap Placed

PERMITS MAY BEREQUIRED !!

Embankment ConstructionEmbankment ConstructionDos and DoDos and Do NotsNots

DO remove unsuitable soils beforeplacing fill

DO compact fill materialsDO keep slopes as flat as possibleDO NOT forget to provide drainage



Over Loading and OverOver Loading and OverSteepening of SlopesSteepening of Slopes

… two other common causes ofembankment slope failures ...

Over Loaded and OverOver Loaded and OverSteepened Slopes OccurSteepened Slopes Occur

as a Result of:as a Result of:

Excessive raising of the trackDisposal of material on the slope“Bank Widening” Erosion of the toe of the slopeUndercutting of the toe of the slope

Over Loading and OverOver Loading and OverSteepening of an Existing SlopeSteepening of an Existing Slope

Failure SurfaceCaused by Overloading Slope

Track CrackWidened,OversteepenedShoulder

Widened,OversteepenedCess

Over Loading SlopeOver Loading Slope

MATERIALREMOVED FROMDITCH PILED ON

CESS.

EMBANKMENTCESS WIDENED

Failure of Over Loaded andFailure of Over Loaded andOver Steepened EmbankmentOver Steepened Embankment

SOIL AND ROCKPLACED ON

SLOPE

POOR SURFACEDRAINAGE ALSO

CONTRIBUTED TOTHIS FAILURE

Undercutting Embankment ToeUndercutting Embankment Toe

Failure SurfaceCaused by Undercutting

of Toe of Slope

Track

Original Slope

Toe of slope undercutby railroad personnelor contractor.

OVERLOAD

STEEPENED SLOPE

Slope Failure Caused bySlope Failure Caused byErosion at ToeErosion at Toe

Slope OverSlope OverSteepenedSteepened bybyErosion at ToeErosion at Toe

Over Steepened andOver Steepened andOver Loaded SlopesOver Loaded Slopes

Dos and DoDos and Do NotsNots

DO protect 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 of

existing embankments

Embankment Flattening andEmbankment Flattening andButtressingButtressing

… flatter slopes are more stable thansteep slopes ...

Cut Benches into Existing Slope- Remove weak or loose soil,

topsoil, vegetation, and debris.

Key into Firm Ground- Remove weak or loose soil,


Drainage Gravel Layer

Compacted Soil Fill (Buttress)

Embankment Stability ImprovedEmbankment Stability Improvedby Flattening the Slopeby Flattening the Slope

Drainage Installed in Existing Embankment

Extend Drainthrough New Fill

Flood Water Level

Low Water Level

Riprap Slope Protection

Compacted Soil Fill (Buttress)

Normal Water Level

Filter Layer(s)

Cut Benches into Existing Slope- Remove weak or loose soil,


Key into Firm Ground- Remove weak or loose soil,


Drainage Gravel Layer

Embankment Stability ImprovedEmbankment Stability Improvedby Buttressing the Slopeby Buttressing the Slope

Drainage Installed in Existing Embankment

Extend Drainthrough New Fill

Flattened SlopeFlattened Slope

Slope Repair, Flattening or ButtressingSlope Repair, Flattening or Buttressingwith Large Rock is Not Recommendedwith Large Rock is Not Recommended

Track Sinkhole Caused by Erosion ofEmbankment Material into Voids

Big Rocks

Voids (air space)Embankment

Slope Repair, Flattening or Buttressing withSlope Repair, Flattening or Buttressing withWellWell--Graded Rock and Filter LayerGraded Rock and Filter Layer

(if necessary) is Preferred(if necessary) is Preferred

Mix of Particle Sizes -Smaller Rock and Gravel FillingVoids Between Larger Rocks

Track

Sand and Gravel Filter(one or more layers)

Embankment

Embankment ButtressingEmbankment Buttressingand Slope Flatteningand Slope Flattening

Dos and DoDos and Do NotsNots

DO construct slopes as flat aspractical

DO use compacted soil or well-graded rock and filter layers

DO provide drainageDO NOT use big rock



Riprap Erosion ProtectionRiprap Erosion Protection

… a routine erosion protectionmeasure that is often constructed

incorrectly …

Washout at aWashout at alocationlocation

where riprapwhere ripraphad beenhad beendumpeddumped

Rock that has been Dumped down aRock that has been Dumped down aSlope is Subject to FailureSlope is Subject to Failure

LARGEROCK AT

BOTTOM OFSLOPE

SMALLROCK ATTOP OFSLOPE

However, During EmergencyHowever, During EmergencySituations Dumping Riprap may beSituations Dumping Riprap may bethe Practical and Timely Solutionthe Practical and Timely Solution

SMALLROCK ATTOP OFSLOPE

LARGEROCK ATBOTTOMOF SLOPE

Prepare Slope for Riprap PlacementPrepare Slope for Riprap Placement

EXCAVATORPLACINGRIPRAP Start at the bottom of the slope

Key Riprap into Stream BedKey Riprap into Stream Bed

*** PERMITS REQUIRED ***

Place and Compact RiprapPlace and Compact Riprap

FilterGravel

Engineering assistance is recommended forsizing riprap and filter materials

Completed Riprap Slope ProtectionCompleted Riprap Slope Protection

RiprapRiprap PlacedPlaced at Culvert Outletsat Culvert Outlets

*** PERMITS MAY BE REQUIRED ***

Riprap Erosion ProtectionRiprap Erosion ProtectionDos and DoDos and Do NotsNots

DO use well-graded properly sized rocks DO use filter layers (if appropriate) DO key riprap along bottom and at ends DO get permits DO get engineering assistance DO NOT dump riprap unless absolutely

necessary



Record KeepingRecord Keeping

… a critical part of cost effectiveresource management …

What to RecordWhat to Record

LocationName of person

making recordentry

Date and timeDescription of

problem

Length of trackaffected

Description of siteMeasurementsRecent weatherRepairs undertaken

Record KeepingRecord KeepingDos and DoDos and Do NotsNots

DO keep a record for each locationDO include description of problem

and repairsDO be accurateDO document recent weatherDO NOT rely on memory - write

things down as soon as practical

Water is a factor in most soft tracksituations, and …

Dos and DoDos and Do NotsNots SummarySummary

DRAINAGE

DRAINAGE

DRAINAGE

DRAINAGE

SURFACE

DRAINAGE

TRENCH

DRAINS

CU

LVER

TS

GROUNDWATER

GROUNDWATER

DO drain surface water awayfrom track

DO maintain culverts and installproperly

DO NOT let water pondDO provide subsurface drainage

Dos and DoDos and Do NotsNots SummarySummary

DO NOT ignore ballast pocketsDO NOT overload, oversteepen,

or undercut slopesDO properly construct fills and

riprapDO keep records

Dos and DoDos and Do NotsNots SummarySummary(cont.)(cont.)

Get the Help of aGet the Help of aGeotechnical Engineer WhenGeotechnical Engineer When

AppropriateAppropriate

Documents

DOs and DO NOTs of Subgrade Maintenance Australian Rail ... · DOs and DO NOTs of Subgrade Maintenance Australian Rail Track Corporation, LTD. Why are we here? Improve Safety Improve