EFFECT OF COAL DUST ON RAILROAD BALLAST …s/fall08/Tutumluer - 10_10...Direct shear box test...

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EFFECT OF COAL DUST ON EFFECT OF COAL DUST ON RAILROAD BALLAST STRENGTH RAILROAD BALLAST STRENGTH AND STABILITYAND STABILITY

ByBy

Erol TutumluerErol TutumluerWilliam (Zach) William (Zach) DombrowDombrowHaiHai HuangHuang

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IntroductionIntroductionProblem StatementProblem StatementFouling Mechanism / Need for Laboratory StudyFouling Mechanism / Need for Laboratory Study

Mechanical Properties of Coal Dust Mechanical Properties of Coal Dust Grain Size AnalysisGrain Size AnalysisAtterbergAtterberg LimitsLimitsSpecific GravitySpecific GravityOptimum Moisture Content (OMC)Optimum Moisture Content (OMC)TriaxialTriaxial TestsTestsDirect Shear TestsDirect Shear Tests

Clean and Coal Dust Fouled Ballast BehaviorClean and Coal Dust Fouled Ballast BehaviorLarge Direct Shear Box TestsLarge Direct Shear Box Tests

ConclusionsConclusionsAcknowledgementAcknowledgement

OUTLINE

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CoalCoal is the leading source of energy is the leading source of energy generation in the U.S. In 2003, 90% of the generation in the U.S. In 2003, 90% of the total coal production, (1.07 billion tons) was total coal production, (1.07 billion tons) was driven by the electric power sector driven by the electric power sector ((BankowskiBankowski et al., 2006).et al., 2006).

CoalCoal transportationtransportation in the U.S. strongly in the U.S. strongly relies on rail transport. Approximately relies on rail transport. Approximately 72% of coal deliveries to U.S. power plants 72% of coal deliveries to U.S. power plants are made by rail transport (EIA, 2006).are made by rail transport (EIA, 2006).

INTRODUCTION

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Unexpected operating flaws on existing rail Unexpected operating flaws on existing rail lines reduce the coal production lines reduce the coal production FForor example: From 2000 to 2005, BNSF/UP Joint example: From 2000 to 2005, BNSF/UP Joint Line transported only Line transported only 325325--million tons of the million tons of the 348348--million total forecast value due to operating million total forecast value due to operating problemsproblems

In 2005, coal dust accumulation in track In 2005, coal dust accumulation in track ballasts caused 2 derailments as a result of ballasts caused 2 derailments as a result of

•• Moisture accumulationMoisture accumulation•• Decreased stability of the tracksDecreased stability of the tracks

It threatened to delay the supply of It threatened to delay the supply of coal to power plantscoal to power plants

INTRODUCTION (CONT’D)

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ORIN LINE – GILLETTE, WYSOUTH POWDER RIVER BASIN

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MP 91

MP 96

BALLAST FOULING IN ORIN LINE 7/24/07

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BALLAST FOULING IN ORIN LINE 7/24/07

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BALLAST FOULING IN MP 37 ORIN LINE 7/24/07

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INTRODUCTION – PROBLEM STATEMENT

As ballast ages, fine grained materials progressively fill the void spaces resulting in fouled ballast Coal Dust Fouled Ballast has been indentified as a contributing factor to recent derailments on the BNSF/UP joint line out of the Powder River Basin, WY

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Cl ean Sampl eFoul ed Sampl e

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INTRODUCTION – PROBLEM STATEMENT

Current methods of track inspection including visual assessment, pumping and ponding at ballast toe, etc., lack the necessary techniques to accurately quantify ballast fouling condition except for

Ground Penetrating Radar

Strength properties of coal dust fouled ballast to be investigated in Laboratory Experiments

Horn Antenna

GPSVideo Camera

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INTRODUCTION – FOULING MECHANISM

Critical Phases of Fouling

Clean Partially to Fully Fouled Heavily Fouled

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Coal Dust (primarily carbon and hydrogen) has never been identified as a significant ballast fouling material to cause the source of multiple derailments and widespread track failure

Typical foulants identified in Railroad Texts (Selig and Waters, 1994)

76% ballast breakdown13% underlying granular layer7% surface materials (such as coal dust)3% subgrade materials1% tie breakdown

MECHANICAL PROPERTIES OF COAL DUST

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Gradation

• Grain Size Distributionestablished by a set of sieves

• Sieve analysis performed acc. to weight of sample retained on each sieve and converted to percent passing each sieve.

• Gradation Curve - Graphical plot of sieve analysis

1-1/2 in.1 in.3/4 in.1/2 in.3/8 in.1/4 in.

Size of theopening in the sieve

Below 1/4 in.No. 4 - 4.76 mmNo. 10 - 2.00No. 20 - 0.84No. 40 - 0.42No. 100 - 0.147No. 200 - 0.075 mm

GRAIN SIZE DISTRIBUTION

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Grain Size Analysis


Close up view

The coal dust sample was collected from The coal dust sample was collected from Orin line Orin line milepost 62.4milepost 62.4 and was sampled on March 10, 2007and was sampled on March 10, 2007

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Grain Size Analysis (ASTM C 136, ASTM C 117)


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Sieve size (in)

% finer (by weight)

24% fines content 24% fines content (passing No. 200 sieve (passing No. 200 sieve or 0.075 mm) by weightor 0.075 mm) by weight

••DDmaxmax = 0.187 in.= 0.187 in.••DD50 50 = 0.030 in.= 0.030 in.

COAL DUST LOOKS LIKE A SAND, BUT WE WILL SEE LATER ACTS LIKE A VERY FINE CLAY

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Plastic Limit (PL) Water content where 1/8" soil thread

begins to crumble by rollingLiquid Limit (LL)

Water content where soil halves close 1/2” at 25 drops of Casagrande’s cup

Plasticity Index (PI)

PI = LL − PL

Very important soil propertyA beach sand is non-plastic

w = 0 SL PL LL Increasing water content, w (%)

non-plastic plastic range Soil acts as a viscous fluid

PI = LL − PL

ATTERBERG LIMITS

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Atterberg LimitsPlastic Limit (PL) = 50%Liquid Limit (LL) = 91%Plasticity Index (PI) = 41%


Weak Soil Examples (Terzaghi et al., 1996)Panama organic silt:Panama organic silt:•• PL: 17%PL: 17%•• LL: 55%LL: 55%•• PI: 38%PI: 38%

Venezuela Clay:Venezuela Clay:•• PL: 25%PL: 25%•• LL: 40%LL: 40%•• PI: 15%PI: 15%

DupontDupont Clay:Clay:•• PL: 26%PL: 26%•• LL: 53%LL: 53%•• PI: 27%PI: 27%CH soil, 55% clay, CH soil, 55% clay, 42% silt42% silt

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The ratio of the density of solid constituents to the density of water (generally at 68oF) is called the specific gravity of solid constituents

Specific gravity of the coal dust: 1.28

Specific gravity of clay particles: 2.5 – 2.9

Specific gravity of sand particles: 2.65


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How much solid material can you pack in a unit volume?

Compaction is the process of increasing soil density and strength by adjusting its water content

Optimum MC

Moisture Content (%)

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+

++

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+

Dry density Max

Dry Density

COMPACTION TEST

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Standard Proctor Compaction (ASTM D698)Standard Proctor Compaction (ASTM D698)


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25.0 30.0 35.0 40.0 45.0Water content (%)

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sity

(pcf

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Zero Air Voids Curve

Optimum water Optimum water content (OMC): content (OMC): 35% 35% High!High!

Maximum dry Maximum dry density (MDD): density (MDD): 54.2 54.2 pcfpcf Low!Low!

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Standard Proctor Compaction Test (ASTM D 698)Standard Proctor Compaction Test (ASTM D 698)

Standard Proctor compaction test results for some Standard Proctor compaction test results for some known weak soils:known weak soils:

Lean Lean siltysilty clay:clay:•• OMC: 17%OMC: 17%•• MDD: 108 MDD: 108 pcfpcf

Heavy clay:Heavy clay:•• OMC: 21%OMC: 21%•• MDD: 102 MDD: 102 pcfpcf

LoessialLoessial silt:silt:•• OMC: 18%OMC: 18%•• MDD: 105 MDD: 105 pcfpcf

DupontDupont clay:clay:•• OMC: 24%OMC: 24%•• MDD: 98 MDD: 98 pcfpcfCH soil, 55% clay, CH soil, 55% clay, 42% silt42% silt

Coal DustCoal Dust::•• OMC: OMC: 35%35%•• MDD: MDD: 54.2 54.2 pcfpcf

COMPACTION TEST RESULTS

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Triaxial (Unconsolidated-Undrained) Tests


•• ServoServo--pneumatic test framepneumatic test frame used as UTM• 2 in. in diameter by 4 in. high specimens

Train Wheel LoadTrain Wheel Load

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Triaxial Test Results

The internal friction angle (φ) of the coal dust is approximately 1.8o, almost equal to zero for such undrained conditions


C.P.=6 psiC.P.=4 psiC.P.=2 psiUnconfined

2Shear Stress

(psi)

Normal Stress (psi)

2 4 6 8 10

1

1,8

1°

τmax = cohesion (c) + σn tan φ00

Unconfined Compressive Strength, Qu = 3 psi Very Low!

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C.P. = 2 psiC.P. = 4 psiC.P. = 6 psiUnconfined

QuQu = 3.5 psi= 3.5 psi

OMC = 35%OMC = 35%

SHEAR STRENGTH TEST RESULTS – COAL DUST

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Axial Strain, %

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MC = 23 % DD = 103.5 pcfQu = 53 psi

MC = 26 % DD = 98 pcfQu = 32 psi

Dupont Clay – Opt. Moisture = 24%

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MC = 23 % DD = 103.5 pcfQu = 53 psi

MC = 26 % DD = 98 pcfQu = 32 psi


MC = 26 % DD = 98 pcfQu = 32 psi

MC = 35 % DD = 54 pcfQu = 3.5 psi

Coal DustOpt. Moisture = 35%

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Axi

al S

tres

s, p

si

MC = 23 % DD = 103.5 pcfQu = 53 psi

MC = 26 % DD = 98 pcfQu = 32 psi


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MC = 23 % DD = 103.5 pcfQu = 53 psi

MC = 26 % DD = 98 pcfQu = 32 psi


MC = 26 % DD = 98 pcfQu = 32 psi

MC = 35 % DD = 54 pcfQu = 3.5 psi

Coal DustOpt. Moisture = 35%

Approximately10 times lowerthan weak DuPont Clayat optimummoisture content

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Direct Shear (Shear Box) Tests


Coal dust samples at different water contentsdifferent water contents sheared horizontally in a 3.94 in. x 3.94 in. (100mm x 100mm)shear box under different normal loads;different normal loads; relation between the normal stress and shear stress established

Normal Force

Constant Speed Shear Displacement

Fixed Upper Box

Normal Force

Constant Speed Shear Displacement

Fixed Upper Box

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Direct Shear Test Results


Moisture Content

(%)

Internal Friction Angle, Φ (Degrees)

tan Φ Cohesion Intercept,

C (psi)

33 34.1 0.68 1.1135 33.53 0.66 1.2337 31.83 0.62 1.1339 27.22 0.51 1.0741 21.91 0.4 1.0143 19.23 0.35 0.81

Drained Drained ConditionsConditions-- grain to grain grain to grain contact friction contact friction

47% decrease in 47% decrease in shear strengthshear strength

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Direct shear tests were conducted at the University of Illinois on both clean and coal dust fouled ballast samples of granite aggregate

Comparison of test results can provide better understanding of fouling mechanisms

CLEAN AND COAL DUST FOULED BALLAST BEHAVIOR

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Clean Granite Ballast Sample (AREMA No. 24) from Clean Granite Ballast Sample (AREMA No. 24) from Gillette, WY and commonly used in Powder River BasinGillette, WY and commonly used in Powder River Basin


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Specific gravity 2.62Unit weight 93 pcfCompacted Air Voids 43%

Percent Passing

in. mm %

2.5 63.5 1002 50.8 82

1.5 38.1 181 25.4 0

Sieve Size

Granite

Gradation

Dmax = 2.5 in.

Dmin = 1 in.

D50 = 1.77 in.

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Large Direct Shear Equipment


12 in. x 12 in.12 in. x 12 in.square boxsquare box

66--in. deep lower boxin. deep lower box33--in. deep upper boxin. deep upper box

up to 30up to 30--kip loadingkip loading

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Direct shear box test procedureObtain 54 lbs. (24.5 kg) of ballast aggregateCompact ballast sample into lower box using two lifts

Use vibratory compactor on top of a flat plexiglas compaction platform and compact until no noticeable movement of particles is observed


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Direct shear box test procedure (continued)Obtain prescribed weight of coal dust and water

Spread coal dust over compacted ballast and shake down the coal dust using vibratory compactor. Place upper ring on and align ring with the lower box.


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Direct shear box test procedure (continued)Place box and ring assembly into shearing apparatus

Three normal pressures (25, 35, and 45 psi) were used; Shearing rate: 0.48 in./min; Maximum strain recorded: 15%


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Direct Shear Tests Results

Coal dust fouling fines content: 0%, 5%, 15%, and 0%, 5%, 15%, and 25% by weight of ballast25% by weight of ballast

Coal dust moisture state: Dry and wet (35% OMC) Dry and wet (35% OMC)

25% coal dust by weight 25% coal dust by weight completely filled the voids in the clean ballast structure – ““fully fouledfully fouled”” stagestage

Any coal dust fouling beyond this percentage should Any coal dust fouling beyond this percentage should be considered as heavily fouled ballast as aggregate be considered as heavily fouled ballast as aggregate to aggregate contact is lost to aggregate contact is lost


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Shear Stress (psi)

Normal Stress (psi)

Clean

5% Dry

5% Wet

15% Dry

15% Wet

25% Dry

25% Wet

*R2 ranges from 0.97 to 0.99

Fully fouled with Fully fouled with wet coal dustwet coal dust

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Condition Fouling % * Cohesion, c (psi) φ (rad.) φ (deg.) Max Shear Stress, τmax = c+ σNtan(φ) Regression Coef, R2

Clean 0 15.24 1.022 45.6 τmax = 15.24+σNtan(43.9°) 0.99

5 13.96 0.991 43.9 τmax = 13.96+σNtan(43.9°) 0.99

15 13.46 0.773 36.2 τmax = 13.46+σNtan(36.2°) 0.99

25 10.90 0.688 36.6 τmax = 10.90+σNtan(36.6°) 0.97

5 8.89 0.963 44.7 τmax = 8.89+σNtan(44.7°) 0.99

15 11.12 0.731 37.7 τmax = 11.12+σNtan(37.7°) 0.99

25 5.10 0.744 34.5 τmax = 5.102+σNtan(34.5°) 0.97* percentage by ballast weight

Dry

Wet (OMC)

Moisture Content

(%)

Internal Friction Angle, Φ (Degrees)

tan Φ Cohesion Intercept,

C (psi)

33 34.1 0.68 1.1135 33.53 0.66 1.23

Similar to the friction Similar to the friction angle of coal dust itself angle of coal dust itself

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Mechanical properties of representative coal dust coal dust samples obtained from the Powder River Basin samples obtained from the Powder River Basin (PRB) joint line(PRB) joint line in Wyoming were determined for the first time through laboratory testing at the Univ. of Illinois

Coal Dust Liquid Limit = 91% Coal Dust Liquid Limit = 91% –– VERY HIGH! VERY HIGH! Coal Dust Optimum Moisture Content (OMC) = 35% Coal Dust Optimum Moisture Content (OMC) = 35% ––much higher than typical weak soils!much higher than typical weak soils!Coal Dust can absorb and hold a lot of water when Coal Dust can absorb and hold a lot of water when compared to clays and siltscompared to clays and siltsTriaxialTriaxial Shear Strength of Coal Dust at OMC = 3 psi Shear Strength of Coal Dust at OMC = 3 psi ––VERY LOW! VERY LOW! Coal Dust friction angle at OMC = 33.5Coal Dust friction angle at OMC = 33.5oo indicated a indicated a large REDUCTION with increasing moisture content large REDUCTION with increasing moisture content

SUMMARY AND CONCLUSIONS

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SUMMARY AND CONCLUSIONS

Large-sized direct shear (shear box) laboratory tests conducted at the Univ. of Illinois on granite ballast on granite ballast samples also obtained from the Powder River samples also obtained from the Powder River Basin (PRB) joint lineBasin (PRB) joint line in Wyoming to investigate the strength and deformation characteristics of both clean (new) and fouled ballast at various stages

The highest shear strength values were obtained from the The highest shear strength values were obtained from the clean clean ballast ballast at all applied normal stress levelsat all applied normal stress levels

When ballast samples were fouled, the shear strength always When ballast samples were fouled, the shear strength always decreased. decreased. Wet (35% OMC) coal dust fouling Wet (35% OMC) coal dust fouling resulted in the resulted in the lower lower ballast shear strengths ballast shear strengths than dry coal dust fouling. than dry coal dust fouling.

For the fully fouled case with 25% wet coal dust by weight of For the fully fouled case with 25% wet coal dust by weight of ballast, internal friction angle and cohesion obtained were ballast, internal friction angle and cohesion obtained were equivalent to those properties of the wet coal dust itselfequivalent to those properties of the wet coal dust itself

Even more drastic strength reductions can be realized when Even more drastic strength reductions can be realized when dry coal dust is subjected to inundation and 100% saturation dry coal dust is subjected to inundation and 100% saturation

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Effect of First Time Saturation Effect of First Time Saturation (6 in. accumulation)(6 in. accumulation)

Dry Coal Dust that has never been saturated canDry Coal Dust that has never been saturated canhave higher strength propertieshave higher strength propertieshold excessive moisture when it rains or snowshold excessive moisture when it rains or snows

When dry coal dust is wetted, this results in a When dry coal dust is wetted, this results in a drastic loss of strengthdrastic loss of strengthU

ncon

fined

Com

pres

sive

Str

engt

h, Q

u

Moisture Content

UnsoakedSpecimen

OMC

SoakedSpecimen

Unc

onfin

ed C

ompr

essi

ve S

tren

gth,

Qu

Moisture Content

UnsoakedSpecimen

OMC

SoakedSpecimen

CONDITIONS OF 2005 DERAILMENTS

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Burlington Northern Santa Fe(BNSF) Railroad Co.

Mr. Henry Lees with BNSF

Kivanc Avrenli at UIUC

ACKNOWLEDGEMENTSACKNOWLEDGEMENTS

41UIUC RAILROADENGINEERING

www.BCR2A.ORGJune 29 - July 2, 2009

EFFECT OF COAL DUST ON RAILROAD BALLAST …s/fall08/Tutumluer - 10_10...Direct shear box test...

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