View
3
Download
0
Category
Preview:
Citation preview
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
Presentation OutlinePresentation Outline
Soft TrackBallast PocketsDrainageCulvertsConstruction PracticesOver Steepened SlopesRiprapRecord Keeping
Soft Track Ballast PocketsDrainageCulvertsConstruction PracticesOver Steepened SlopesRiprapRecord Keeping
Presentation OutlinePresentation Outline
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
Presentation OutlinePresentation Outline
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
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
Presentation OutlinePresentation Outline
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 …
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
Presentation OutlinePresentation Outline
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
Culvert IssuesCulvert Issues
Maintenance Installation Inlet Protection and Trash RacksOutlet Erosion Protection
Culvert InstallationCulvert Installation
… when done properly ensures thatthe culvert and embankment
function properly …
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
Culvert IssuesCulvert Issues
Maintenance Installation Inlet Protection and Trash RacksOutlet Erosion Protection
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
Culvert IssuesCulvert Issues
Maintenance Installation Inlet Protection and Trash RacksOutlet Erosion Protection
Erosion Below CulvertErosion Below CulvertOutletsOutlets
… another all too common contributorto embankment failures …
Erosion BelowErosion BelowOverflowOverflowCulvertsCulvertsExtendExtend
Culverts orCulverts orProtect SlopeProtect Slope
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
Presentation OutlinePresentation Outline
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
Close up of Bulge in EmbankmentClose up of Bulge in Embankmentand Offset Flumeand Offset Flume
BULGE INEMBANKMENTAND 2- METER
OFFSET IN FLUME
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
? ?
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
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
Track Components Soft Track Ballast PocketsDrainage and CulvertsConstruction PracticesOver Steepened SlopesRiprapRecord Keeping
Presentation OutlinePresentation Outline
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
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,
topsoil, vegetation, and debris.
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,
topsoil, vegetation, and debris.
Key into Firm Ground- Remove weak or loose soil,
topsoil, vegetation, and debris.
Drainage Gravel Layer
Embankment Stability ImprovedEmbankment Stability Improvedby Buttressing the Slopeby Buttressing the Slope
Drainage Installed in Existing Embankment
Extend Drainthrough New Fill
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
Track Components Soft Track Ballast PocketsDrainage and CulvertsConstruction PracticesOver Steepened SlopesRiprapRecord Keeping
Presentation OutlinePresentation Outline
Riprap Erosion ProtectionRiprap Erosion Protection
… a routine erosion protectionmeasure that is often constructed
incorrectly …
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
Place and Compact RiprapPlace and Compact Riprap
FilterGravel
Engineering assistance is recommended forsizing riprap and filter materials
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
Track Components Soft Track Ballast PocketsDrainage and CulvertsConstruction PracticesOver Steepened SlopesRiprapRecord Keeping
Presentation OutlinePresentation Outline
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
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.)
Recommended