U.S. Department of 

Transportation

Federal Railroad 

Administration

Slab Track Field Test and Demonstration 

Program for Shared Freight and High-Speed 

Passenger Service

Office of Research

and Development

Washington, DC 20590

DOT/FRA/ORD-10/10 Final Report

August 2010
NOTICE

This document is disseminated under the sponsorship of the 

Department of Transportation in the interest of information 

exchange. The United States Government assumes no liability for 

its contents or use thereof.

NOTICE

The United States Government does not endorse products or 

manufacturers. Trade or manufacturers’ names appear herein 

solely because they are considered essential to the objective of this 

report.
i

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 

collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson 

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

August 2010

3. REPORT TYPE AND DATES COVERED

Technical Report

4. TITLE AND SUBTITLE

Slab Track Field Test and Demonstration Program for Shared Freight and High-Speed 

Passenger Service

5. FUNDING NUMBERS

RR19/HG272

6. AUTHOR(S)

Dingqing Li

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

U.S. Department of Transportation

Research and Innovative Technology Administration

John A. Volpe National Transportation Systems Center

55 Broadway 

Cambridge MA 02142-1093

8. PERFORMING ORGANIZATION 

REPORT NUMBER

DOT-VNTSC-FRA-10-05

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Department of Transportation 

Federal Railroad Administration

Office of Research and Development

Washington, DC 20590

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

DOT/FRA/ORD-10/10

11. SUPPLEMENTARY NOTES 

COTR: Ted Sussman

12a. DISTRIBUTION/AVAILABILITY STATEMENT

This document is available to the public through the FRA Web site at http://www.fra.dot.gov.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

Two types of slab tracks were installed on the High Tonnage Loop at the Facility for Accelerated Service Testing. Direct fixation 

slab track (DFST) and independent dual block track (IDBT) were installed into a 5-degree curve with 4-inch superelevation. The 

total slab track test section was 500 feet (ft) long, which consisted of 250 ft of IDBT and 250 ft of DFST. This program was 

conducted to demonstrate the durability of the slab track for 39-ton axle loads while maintaining the track geometry conditions of 

a Class 9 track. More specifically, the program was carried out to characterize slab track stiffness conditions, to quantify slab 

track dynamic responses and long-term performance under heavy axel load train operation, and to provide the test data for 

validating slab track analysis and design methodologies for shared heavy-freight and high-speed train service.

14. SUBJECT TERMS

Slab track, ballasted track, high-speed train, heavy axle load traffic

15. NUMBER OF PAGES

126

16. PRICE CODE

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

19. SECURITY CLASSIFICATION

OF ABSTRACT

Unclassified

20. LIMITATION OF ABSTRACT

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. 239-18

298-102
ii

METRIC/ENGLISH CONVERSION FACTORS

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE)

1 inch (in) = 2.5 centimeters (cm) 1 millimeter (mm) = 0.04 inch (in)

1 foot (ft) = 30 centimeters (cm) 1 centimeter (cm) = 0.4 inch (in)

1 yard (yd) = 0.9 meter (m) 1 meter (m) = 3.3 feet (ft)

1 mile (mi) = 1.6 kilometers (km) 1 meter (m) = 1.1 yards (yd)

1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE)

1 square inch (sq in, in2) = 6.5 square centimeters (cm2) 1 square centimeter (cm2) = 0.16 square inch (sq in, in2)

1 square foot (sq ft, ft2) = 0.09 square meter (m2) 1 square meter (m2) = 1.2 square yards (sq yd, yd2)

1 square yard (sq yd, yd2) = 0.8 square meter (m2) 1 square kilometer (km2) = 0.4 square mile (sq mi, mi2)

1 square mile (sq mi, mi2) = 2.6 square kilometers (km2) 10,000 square meters (m2) = 1 hectare (ha) = 2.5 acres

1 acre = 0.4 hectare (he) = 4,000 square meters (m2)

MASS - WEIGHT (APPROXIMATE) MASS - WEIGHT (APPROXIMATE)

1 ounce (oz) = 28 grams (gm) 1 gram (gm) = 0.036 ounce (oz)

1 pound (lb) = 0.45 kilogram (kg) 1 kilogram (kg) = 2.2 pounds (lb)

1 short ton = 2,000 pounds 

(lb)

= 0.9 tonne (t) 1 tonne (t) =

=

1,000 kilograms (kg)

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE)

1 teaspoon (tsp) = 5 milliliters (ml) 1 milliliter (ml) = 0.03 fluid ounce (fl oz)

1 tablespoon (tbsp) = 15 milliliters (ml) 1 liter (l) = 2.1 pints (pt)

1 fluid ounce (fl oz) = 30 milliliters (ml) 1 liter (l) = 1.06 quarts (qt)

1 cup (c) = 0.24 liter (l) 1 liter (l) = 0.26 gallon (gal)

1 pint (pt) = 0.47 liter (l)

1 quart (qt) = 0.96 liter (l)

1 gallon (gal) = 3.8 liters (l)

1 cubic foot (cu ft, ft3) = 0.03 cubic meter (m3) 1 cubic meter (m3) = 36 cubic feet (cu ft, ft3)

1 cubic yard (cu yd, yd3) = 0.76 cubic meter (m3) 1 cubic meter (m3) = 1.3 cubic yards (cu yd, yd3)

TEMPERATURE (EXACT) TEMPERATURE (EXACT)

[(x-32)(5/9)] F = y C [(9/5) y + 32] C = x F

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 3 4 5

Inches

Centimeters 0 1 2 3 4 5 6 7 8 9 10 11 12 13

QUICK FAHRENHEIT - CELSIUS TEMPERATURE CONVERSION

 -40° -22° -4° 14° 32° 50° 68° 86° 104° 122° 140° 158° 176° 194° 212°

 

°F

 °C -40° -30° -20° -10° 0 ° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100°

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and 

Measures. Price $2.50 SD Catalog No. C13 10286 Updated 6/17/98
iii

Acknowledgments

This project was jointly funded by the Portland Cement Association (PCA) and the Federal 

Railroad Administration (FRA) under its Next Generation High-Speed Rail Program. David 

Bilow of PCA served as the program manager. Donald Plotkin of FRA, Robert McCown, 

formerly of FRA, and Andrew Sluz and Ted Sussman of the Volpe National Transportation 

Systems Center provided advice during the test program. Mr. Sluz and Mr. Sussman also served 

as contracting officer technical representatives for this project. 

Guidance and contributions were provided from the expert panel members of the Cooperative 

Concrete Slab Track Research and Demonstration Program, suppliers, and other PCA and 

Construction Technology Laboratories personnel, including Steven Chrismer, Nathan Higgins, 

Richard Lanyi, Mohammad Longi, Nicholas Skoutelas, Jan Zicha, Bernard Sonneville, William 

Osler, Shiraz Tayabji, Claire Ball, Hamid Lotfi, William Kucera, and Gene Randich. 

Transportation Technology Center, Inc. (TTCI), employees Kenneth Laine, Mark White, David 

Williams, Ira Kalb, Rick Montoya, and Rachel Anaya contributed significantly to the slab track 

demonstration and testing program. TTCI student intern Matt Aguirre assisted with data 

reduction and analysis.
iv

Contents

Executive Summary........................................................................................................................ 1

1. Introduction............................................................................................................................ 5

1.1 Background...................................................................................................................... 5

1.2 Objective .......................................................................................................................... 6

1.3 Approach.......................................................................................................................... 6

1.4 Scope................................................................................................................................ 7

2. Design and Construction of Slab Track Test Section ............................................................ 8

2.1 HTL and Load Environment............................................................................................ 8

2.1.1 HTL and Section 38 ................................................................................................... 8

2.1.2 Operation and Load Environment at FAST............................................................... 9

2.2 Design and Construction of Slab Track Test Section .................................................... 12

2.2.1 Slab Track Design and Construction ....................................................................... 12

2.2.2 Subgrade .................................................................................................................. 15

2.2.3 Subbase .................................................................................................................... 15

2.2.4 Direct Fixation Slab Track....................................................................................... 17

2.2.5 Independent Dual Block Track ................................................................................ 18

2.2.6 Transitions................................................................................................................ 20

2.2.7 Rail........................................................................................................................... 22

2.2.8 Completion of Slab Track Construction .................................................................. 22

2.3 Design and Construction................................................................................................ 24

2.3.1 Design ...................................................................................................................... 24

2.3.2 Construction Challenges.......................................................................................... 24

3. Track Geometry Performance of Slab Track ....................................................................... 26

3.1 Objective ........................................................................................................................ 26

3.2 Tonnage Accumulation on Slab Track .......................................................................... 26

3.3 Track Geometry Measurement Methods ....................................................................... 26

3.3.1 Top-of-Rail Elevation Survey.................................................................................. 27

3.3.2 Slab Movement Survey............................................................................................ 27

3.3.3 Track Geometry Measurement System.................................................................... 27

3.3.4 Other Measurements................................................................................................ 28

3.4 Initial Track Geometry of Slab Track............................................................................ 29
v

3.4.1 Surface ..................................................................................................................... 29

3.4.2 Gage ......................................................................................................................... 31

3.4.3 Alignment ................................................................................................................ 31

3.5 Track Geometry Maintenance and Change Over Time ................................................. 32

3.5.1 Alignment ................................................................................................................ 32

3.5.2 Gage ......................................................................................................................... 35

3.5.3 Surface of Slab Track and Transitions..................................................................... 36

3.5.4 Cumulative Settlement of Slab Track and Transitions............................................ 36

3.6 Other Observations About the Slab Track Test Section ................................................ 39

4. Slab Track Stiffness Characterization.................................................................................. 40

4.1 Introduction.................................................................................................................... 40

4.2 Vertical Track Modulus Testing .................................................................................... 40

4.2.1 Test Methods............................................................................................................ 40

4.2.2 Test Results and Discussion..................................................................................... 41

4.3 Gage Strength Testing.................................................................................................... 45

5. Dynamic Wheel Load Measurements on Slab Track .......................................................... 49

5.1 Objective ........................................................................................................................ 49

5.2 Test Methods.................................................................................................................. 49

5.2.1 Instrumented Wheelsets........................................................................................... 49

5.2.2 Wayside Load Stations ............................................................................................ 50

5.3 IWS Test Results............................................................................................................ 51

5.3.1 Vertical Wheel Load ................................................................................................ 51

5.3.2 Lateral Wheel Load.................................................................................................. 55

5.4 Wayside Load Station Test Results ............................................................................... 57

5.4.1 Vertical Wheel Load ................................................................................................ 57

5.4.2 Lateral Wheel Load.................................................................................................. 60

6. Deflection of Slab Track Components under HAL ............................................................. 64

6.1 Instrumentation for Deformation Measurement ............................................................ 64

6.1.1 Linear Variable Differential Transformer for Rail-to-Slab Deflection.................... 64

6.1.2 Multidepth Deflectometers for Deformation in Slab, Subbase, and Subgrade........ 65

6.2 Test Results.................................................................................................................... 66

6.2.1 Vertical Rail-to-Slab Deflection .............................................................................. 66
vi

6.2.2 Lateral Rail-to-Slab Deflection................................................................................ 70

6.2.3 Vertical Deformation in Slab, Subbase, and Subgrade Layers................................ 72

7. Subgrade Pressure under Slab Track ................................................................................... 76

7.1 Subgrade Pressure Cell and Installation ........................................................................ 76

7.2 Test Results.................................................................................................................... 77

7.3 Long-Term Use of Subgrade Pressure Cells.................................................................. 79

8. Vibration Attenuation of Slab Track.................................................................................... 81

8.1 Instrumentation for Vibration Measurement ................................................................. 81

8.2 Test Results.................................................................................................................... 82

8.2.1 Analysis in Time Domain ........................................................................................ 82

8.2.2 Analysis in Frequency Domain................................................................................ 86

9. Other Measurements of Slab Track ..................................................................................... 88

9.1 Instrumentation for Strain Measurement ....................................................................... 88

9.2 Test Results.................................................................................................................... 90

9.2.1 Rail Base Bending Strain ......................................................................................... 90

9.2.2 Concrete Surface Strain ........................................................................................... 92

9.2.3 Steel Bar Strain ........................................................................................................ 94

10. Summary and Conclusions .................................................................................................. 98

10.1 Track Geometry Performance of Slab Track ................................................................. 98

10.2 Slab Track Stiffness Characteristics .............................................................................. 98

10.3 Dynamic Wheel/Rail Forces on Slab Track................................................................... 99

10.4 Slab Track Deflection .................................................................................................. 100

10.5 Subgrade Pressure and Deformation under Slab Track ............................................... 100

10.6 Vibration Attenuation .................................................................................................. 100

10.7 Other Performance Parameters.................................................................................... 100

10.8 Additional Notes.......................................................................................................... 101

10.9 Recommendations........................................................................................................ 101

11. References.......................................................................................................................... 102

Appendix A – Report of IDBT Inspection on November 20, 2006.............................................103

Appendix B – Data from January 18, 2007, Test Report............................................................ 112

Abbreviations and Acronyms ..................................................................................................... 114
vii

Illustrations

Figure 1. Test Tracks at TTC......................................................................................................... 8

Figure 2. Tonnage Loop (Slab Track in Section 38) ..................................................................... 9

Figure 3. FAST HAL Train Running on the HTL....................................................................... 10

Figure 4. Distribution of Vertical and Lateral Wheel Loads in the HTL .................................... 11

Figure 5. Distribution of Vertical and Lateral Wheel Loads in Section 38 ................................. 11

Figure 6. Slab Track Plan and Details ......................................................................................... 14

Figure 7. Subgrade Surface for Slab Track Test Section............................................................. 15

Figure 8. Soil Cement Subbase Surface for Slab Track Test Section.......................................... 16

Figure 9. DFST Plan and Details................................................................................................. 17

Figure 10. Construction of DFST Using Top-down Method....................................................... 18

Figure 11. IDBT Plan and Details................................................................................................ 19

Figure 12. Construction of the IDBT Using Top-down Method ................................................. 20

Figure 13. IDBT and DFST Interface Plan and Details............................................................... 20

Figure 14. DFST Transition Design............................................................................................. 21

Figure 15. Base Slab in Transition to the IDBT and DFST Transition ....................................... 22

Figure 16. Views of IDBT (top) and DFST (bottom) following Construction............................ 23

Figure 17. Tonnage Accumulation on Slab Track ....................................................................... 26

Figure 18. TTCI’s Track Geometry Measurement System Attached to an 

Empty Tank Car (left) and TTCI’s Track Loading Vehicle (right) .......................... 28

Figure 19. Initial Rail Surface Elevation Results......................................................................... 29

Figure 20. Initial Track Surface via TGMS................................................................................. 30

Figure 21. Initial Track Gage via TGMS..................................................................................... 31

Figure 22. Initial Track Alignment via TGMS ............................................................................ 32

Figure 23. Hand-String MCO Data Showing Misalignment toward the End of the DFST......... 33

Figure 24. Hand-String MCO Data Showing Correction of Misalignment................................. 33

Figure 25. Change of Track Alignments over Time .................................................................... 34

Figure 26. Lateral (Radial) Movement of the IDBT and DFST Slabs......................................... 35

Figure 27. Change of Track Gage over Time .............................................................................. 35

Figure 28. Change of Track Surface over Time .......................................................................... 36

Figure 29. Cumulative TOR Settlement of Slab Track and Transitions...................................... 38

Figure 30. Fine Sand Deposit and Buildup of Gray Material around IDBT Tie Blocks............. 39
viii

Figure 31. Track Modulus Test Result of Slab Track (IDBT and DFST)................................... 42

Figure 32. In-motion TLV Track Stiffness Test Results ............................................................. 43

Figure 33. Track Modulus Test Result of Transition Track (IDBT and DFST).......................... 44

Figure 34. Track Modulus Test Results of Slab Track (IDBT and DFST) at 169 MGT............. 45

Figure 35. Track Gage Strength Test Results at 2 MGT ............................................................. 47

Figure 36. Track Gage Strength Test Results at 169 MGT ......................................................... 48

Figure 37. Short Test Consist including IWS (2003) .................................................................. 50

Figure 38. Wayside Load Station................................................................................................. 51

Figure 39. Vertical Wheel Loads via IWS (2003)....................................................................... 52

Figure 40. Section 38 (Slab Track) vs. Section 31 (Ballasted Track) 

Vertical Load in 2003 ................................................................................................. 53

Figure 41. Section 38 (Slab Track) Compared with Section 31 (Ballasted Track) 

Vertical Load in 2004 ................................................................................................. 54

Figure 42. Section 38 (Slab Track) Compared with Section 7 (Ballasted Track) 

Vertical Load in 2005 ................................................................................................. 54

Figure 43. Lateral Wheel Loads via IWS (2003)......................................................................... 55

Figure 44. Section 38 (Slab Track) vs. Section 31 (Ballasted Track) Lateral Load in 2003....... 56

Figure 45. Lateral Wheel Loads via IWS (2005)......................................................................... 57

Figure 46. Vertical Wheel Loads via Wayside Load Station (2003): Train Traveling 

in CCW Direction...................................................................................................... 58

Figure 47. Vertical Wheel Loads via Wayside Load Station (2003): Train Traveling 

in the CW Direction .................................................................................................. 59

Figure 48. Vertical Wheel Loads Recorded under FAST Trains from 2003 to 2006.................. 60

Figure 49. Lateral Wheel Loads via Wayside Load Station (2003): Train Traveling 

in the CCW Direction................................................................................................ 61

Figure 50. Lateral Wheel Loads via Wayside Load Station (2003): Train Traveling 

in CW Direction.......................................................................................................... 62

Figure 51. Lateral Wheel Loads Recorded under FAST Trains from 2003 to 2006 ................... 63

Figure 52. Layout of Wayside Transducers for IDBT (also for DFST) ...................................... 64

Figure 53. LVDT for Vertical and Lateral Rail-to-Slab Deflection (IDBT and DFST).............. 65

Figure 54. MDD for Vertical Deformation at Four Different Depths ......................................... 66

Figure 55. MDD before and after Installation in Slab Track....................................................... 66

Figure 56. Vertical Rail-to-Slab Deflection under Short Test Consist Traveling 

in the CCW Direction................................................................................................ 67
ix

Figure 57. Vertical Rail-to-Slab Deflection under Short Test Consist Traveling 

in CW Direction ........................................................................................................ 68

Figure 58. Vertical Rail-to-Slab Deflection under FAST Train (2003–2006)............................. 69

Figure 59. Lateral Rail-to-Slab Deflection under Short Test Consist Traveling 

in CCW Direction ....................................................................................................... 70

Figure 60. Lateral Rail-to-Slab Deflection under Short Test Consist Traveling 

in CW Direction.......................................................................................................... 71

Figure 61. Lateral Rail-to-Slab Deflection under FAST Train (2003–2006).............................. 72

Figure 62. MDD Test Results under Short Test Train Traveling in CCW Direction.................. 73

Figure 63. MDD Test Results under Short Test Train Traveling in CW Direction..................... 74

Figure 64. Subgrade Deformation under FAST Train Traveling in CCW Direction .................. 75

Figure 65. Arrangement of Subgrade Pressure Cells................................................................... 76

Figure 66. Installation of Subgrade Pressure Cells...................................................................... 77

Figure 67. Subgrade Pressure under Short Test Consist.............................................................. 78

Figure 68. Subgrade Pressure under FAST Train........................................................................ 79

Figure 69. Arrangement of Accelerometers for Vibration Measurement.................................... 81

Figure 70. Accelerometers Installed in Slab Track (arrows) and in Transition........................... 82

Figure 71. Vibration Attenuation from Rail-to-Slab (Short Consist in CCW Direction)............ 83

Figure 72. Rail Vibration in Transitions (Short Consist in CCW Direction) .............................. 83

Figure 73. Vibration Attenuation from Rail-to-Slab (Short Consist in CW Direction)............... 84

Figure 74. Rail Vibration in Transitions (Short Consist in CW Direction)................................. 84

Figure 75. Vibration Attenuation from Rail to Slab .................................................................... 85

Figure 76. Rail Vibration in Transitions...................................................................................... 86

Figure 77. Vibration Attenuation in Frequency Domain from Rail to Slab ................................ 87

Figure 78. Arrangement of Strain Gages on Slab Surface and Reinforcement Bars................... 89

Figure 79. Strain Gages Installed on Slab Surface and Steel Bar................................................ 89

Figure 80. Rail Bending Strain under Short Test Consist in CCW Direction ............................. 91

Figure 81. Rail Bending Strain under Short Test Consist in CW Direction (2003) .................... 92

Figure 82. Slab Surface Strains under Short Test Consist in CW Direction ............................... 93

Figure 83. Strains of Top Steel Bars under Short Test Consist in CCW Direction..................... 95

Figure 84. Longitudinal Strains of Bottom Steel Bars................................................................. 96

Figure 85. Lateral Strains of Bottom Steel Bars.......................................................................... 97
x

Tables

Table 1. Milestones of Slab Track Construction ......................................................................... 22

Table 2. Slab Track Test Section Defined by Fastener/Tie Location Number............................ 27

Table 3. Allowable Track Geometry Limits Used in Slab Track Testing ................................... 30
1

Executive Summary

Although slab track for high-speed rail (HSR) has been used for decades in Europe and Japan, its 

use in North America has been limited. With the growth of urban areas and increased congestion 

on highways and airports, more HSR passenger service may be needed. 

In some cases, economic and practical limitations may require passenger and freight trains to 

share at least some segments of the same tracks and right-of-way (ROW), but conventional track 

structures may not be adequate for both types of train services. Conventional track structures 

may not be capable of retaining the tight tolerances required for HSR service while 

simultaneously withstanding heavy axle load (HAL) freight traffic without incurring excessive 

rates of track degradation. To address the needs of both types of rail traffic, an alternative track 

structure may be necessary to ensure adequate stability and reliability. 

In 2000, the Portland Cement Association (PCA) initiated a research program entitled 

Cooperative Slab Track Research and Demonstration Program for Shared Freight and HighSpeed Passenger Service. The objective of the program was to advance concrete slab track 

technology and to demonstrate the capability of slab track to provide a low maintenance and safe 

track structure for shared HSR and HAL freight on U.S. railroads. 

A major part of the cooperative research and demonstration program was the Slab Track Field 

Testing and Demonstration Program for Shared Freight and High-Speed Passenger Service 

project, which was carried out from July 2003 to July 2006 by the Transportation Technology 

Center, Inc. (TTCI), a wholly owned subsidiary of the Association of American Railroads

(AAR), in Pueblo, CO. The program was jointly funded by PCA and the Federal Railroad 

Administration (FRA). 

This testing program was undertaken to demonstrate the durability of slab track for 39-ton axle 

loads while maintaining the track geometry conditions of a Class 9 track. More specifically, the 

testing program was completed to characterize slab track stiffness conditions, to quantify its 

dynamic responses and long-term performance under HAL operation, and to provide test data for 

validating slab track analyses and design methodologies developed for shared HAL freight and 

HSR service.

In July 2003, two types of slab track—direct fixation slab track (DFST) and independent dual 

block track (IDBT)—were installed on the High Tonnage Loop (HTL) at the Facility for 

Accelerated Service Testing (FAST), Transportation Technology Center (TTC), in Pueblo, 

Colorado. The slab track test section in the HTL is in a 5-degree curve with 4-inch 

superelevation. The total slab track section is 500 ft long, consisting of 250 ft of IDBT and 250 

ft of DFST. The transition from each slab to the ballasted track is in the spiral, from the 5-degree 

curve to tangent track. 

The train at FAST consists of 60–80 39-ton axle load cars and runs on the HTL (2.7 miles (mi)) 

lap-by-lap at 40 miles per hour (mph). The direction of train traffic is generally 50 percent 

clockwise (CW) and 50 percent counterclockwise (CCW). In addition, the slab track test section 

was located in a bypass at FAST, which subjected it to roughly 50 percent of total traffic for the 

3 years (yr) of the testing program.
2

The testing program was concluded in the summer of 2006. For 3 yr, a total of 170 million gross 

tons (MGT) of HAL traffic was accumulated on the slab track test section, exceeding the target 

tonnage of 150 MGT. Various measurements were conducted during the 3 yr of testing and 

monitoring to quantify the slab track responses and performance under HAL train operations. 

The following sections give the main conclusions drawn from this testing program.

Track Geometry Performance of Slab Track

The slab track test section on the HTL was demonstrated capable of supporting HAL train 

operations while maintaining the track geometry conditions for Class 9 track. Little track 

geometry degradation was measured after 3 yr of testing and 170 MGT of accumulated traffic. 

No track geometry maintenance was required for surface, alignment, gage, or crosslevel of the 

slab track test section. From the beginning of the testing program until its completion, there was 

little cumulative settlement and little lateral movement of the slab track. 

The surface condition of the slab track was superior to the adjacent ballasted track; however, 

several spot-tamping operations were done in the transition areas to smooth out cumulative 

differential track settlement that accumulated in the ballasted transitions.

Slab Track Stiffness Characteristics 

When measured after the construction of the slab track test section, the IDBT showed an average 

track modulus of 3,000 pound/inch/inch (lb/in/in), whereas the DFST showed an average track 

modulus of 2,100 lb/in/in. These values, especially for the DFST, were lower than originally 

expected. Extremely resilient rubber boots and pads were used in each slab track design.

During the 3-year period, the increase in track modulus for the DFST was moderate, but the 

increase for the IDBT was significant. This increase was caused by the gradual deposit of fine 

sand blowing into spaces between the IDBT components. This was determined during the IDBT 

inspection in November 2006. This process caused an increase in track modulus by limiting the 

deflection of the block ties within the rubber boots. Under the action of passing trains, some of 

the sand in the IDBT was flushed out when mixed with rainwater. This left a fine gray deposit 

around the block ties. Although the IDBT track modulus increased between 2003 and 2006, the

laboratory measured an IDBT pad removed during the inspection, which indicated that the pad 

stiffness was still within tolerance. 

In terms of lateral gage strength, both the IDBT and the DFST slab tracks showed more uniform 

lateral gage strength or stiffness than the adjacent ballasted track. For the DFST, there was a 

significant decrease in gage strength in terms of delta gage (delta gage = loaded gage – unloaded 

gage) measured. From 2 to 169 MGT, delta gage measured under track loading vehicle test 

loads (33-kilopound vertical wheel load and 18-kilopound lateral wheel load) increased an 

average of 0.3 to 0.5 in. For the DFST, rubber pads were installed at the rail-slab interface. 

Extremely resilient pads such as those used in the DFST may be of concern under HAL 

operations. For the IDBT, little gage strength degradation in terms of delta gage was seen, 

although unloaded track gage increased an average of 56.8–57.1 in, with the maximum being 

57.2 in. Compared with the DFST, the resilience of the rubber boots and pads used in the IDBT 
3

had less influence on gage strength or stiffness because of their location at the tie and slab 

interface. 

Dynamic Wheel/Rail Forces on Slab Track 

Because of superior track geometry and resilient pads and boots, the slab track test sections 

generated lower dynamic vertical and lateral wheel loads than the ballasted track test section of 

the same curvature and speed superelevation. The maximum vertical load generated in the slab 

track was 58 kilopounds (kip) as compared with 73 kip generated on the ballasted track with the 

same curvature and speed superelevation. The maximum lateral wheel load generated in the slab 

track was 20 kip as compared with 24 kip in the ballasted track. Note, the slab track test section,

located in a 5-degree curve with 4-inch superelevation, is underbalanced at the nominal train 

operating speed of 40 mph on the HTL; for example, higher vertical wheel loads are applied on 

the high rail than on the low rail.

Slab Track Deflection Response

Slab track deflection occurred primarily between the rail and the concrete slabs due to the 

resilient pads (DFST) or rubber boots/pads (IDBT). Only a small amount of deformation was 

recorded from the underlying subbase and subgrade layers. 

Higher dynamic wheel loads and lower track stiffnesses correspond to larger rail-to-slab 

deflections regardless of the slab track type. For the DFST, the maximum vertical rail-to-slab 

deflection was 0.25 in and the maximum lateral rail-to-slab deflection was 0.1 in, both recorded 

on the high rail. For the IDBT, the maximum vertical rail-to-slab deflection was 0.15 in and the 

maximum lateral rail-to-slab deflection was 0.07 in, again measured on the high rail.

For the DFST from 2003 to 2006, little increase in vertical rail-to-slab track deflection was 

measured. However, an increasing trend was observed of lateral rail-to-slab deflection, which 

appeared consistent with the trend of decreasing gage strength for the DFST. For the IDBT from 

year 2003 to 2006, the general trends for both vertical and lateral rail-to-slab deflections 

measured were decreasing, particularly for the deflections measured on the high rail. These 

results appear to be consistent with the increase in track stiffness for the IDBT slab track.

Subgrade Pressure and Deformation under Slab Track 

The maximum subgrade pressure generated under HAL vehicles was 12 pounds per square inch 

(psi), well below the compressive strength of the subgrade soil at the test site (above 50 psi). 

The relatively low subgrade pressure with respect to the soil strength explains the small amount 

of subgrade deformation generated under the HAL train operation. Under the slab track test 

section, the maximum deformation recorded in the subbase or subgrade was less than 0.06 in.

Vibration Attenuation 

In the slab track test section, vibration attenuation was achieved using rubber pads (DFST) or 

rubber boots/pads (IDBT). The vibration measurements showed significant vibration attenuation 

from the rail to the slab regardless of slab track type. Under HAL train operations at 40 mph, the 

maximum acceleration recorded on the rails ranged between 10 and 25g (absolute value) 
4

whereas the maximum acceleration recorded on the slab ranged between 0.4 and 2g (absolute 

value). On average, attenuation was achieved by a factor of 20. 

Vibration measured on the rails showed no obvious trend between the transitions and the slab 

tracks as well as between high and low rails. Analysis of vibration attenuation in frequency 

domain showed the attenuation of vibration energy across the entire spectrum. 

Slab Track Construction

Design of slab track must adequately account for geologic variations that affect the support of 

the structure. Neither slab track nor ballasted track can bridge or span variations in track support 

like that of a bridge. State of the art ballasted track design procedures require similar data on 

local soil conditions and geology, so this should not be viewed as an additional cost of slab track 

over ballasted track, but rather the cost of building a structure to reduce life-cycle cost by 

reducing future maintenance expense. In a similar manner, the subgrade stabilization completed 

as part of this test should also be conducted for the construction of a state of the art ballasted 

track. 

Slab track construction challenges range from tight tolerances of 1/8 in required to achieve the 

desired track Class 9 compliance, to environmental challenges associated with 

expansion/contraction of the rail. Rail bracing to fight rail movement from expansion and 

contraction was found to be a critical element during the construction of the slab track. 

Adequate bracing was found to be the only way to maintain rail position. An attempt to use 

white paint to reduce the thermal gain of the rail was not found to be effective.

Other Performance Parameters

No rail defect was recorded in the slab track test section for a total of 170 MGT of HAL traffic, 

nor was any weld defect or failure reported for the 14 thermite welds used. For comparison 

purposes, the average weld life in similar 5-degree curves of the HTL is approximately 80 MGT. 

In addition, only a small amount of rail wear and no corrugation were observed in the test 

sections. 

Recommendations

The slab track test section remains in the HTL, and it is planned to remain in track until a reason 

to remove the slab exists, such as a new test, performance problems, or any other concern. As 

the slab track test section continues to be subjected to HAL train operations, it is recommended 

that its performance monitoring continue in terms of track geometry conditions. Future gage 

strength testing is also recommended to determine if gage strength of the DFST may further 

degrade under HAL. Testing of rubber boots or pads in either IDBT or DFST slab for a possible 

temperature increase under train operation or a change of resilient property over time may 

provide further insight regarding their eventual life under HAL train operation. Finally, the 

recommendation is that a test section of slab track be installed in revenue service with shared 

heavy freight and HSR operations.
5

1. Introduction

1.1 Background

Although slab track for HSR has been used for decades in Europe and Japan, its use in the 

United States has been limited. Additional HSR passenger service may be needed in North 

America as urban areas grow and congestion on highways and airports increases. In some cases, 

economic and practical limitations may require passenger and freight trains to share at least some 

segments of the same tracks and ROW. Conventional track structures, however, may not be 

adequate for both types of train services. 

Conventional track structures may not be capable of retaining the tight tolerances required for 

HSR service while simultaneously withstanding HAL freight traffic without incurring excessive 

rates of track degradation. To address the needs of both types of rail traffic, an alternative track 

structure may be necessary to ensure adequate stability and reliability.

In 2000, the Portland Cement Association (PCA) initiated a research program entitled 

Cooperative Slab Track Research and Demonstration Program for Shared Freight and HighSpeed Passenger Service. The objective of the program was to demonstrate concrete slab 

performance under HAL load with Class 9 standards. The research program was planned and 

carried out in the following three phases:

Phase 1: Literature review, development of design methodology, and life-cycle cost study. 

As a result of the Phase 1 study (Tayabji and Bilow, 2001), the DFST and the IDBT forms 

were selected for full-scale laboratory and field demonstration tests. Phase 1 was completed 

by PCA and its subsidiary, Construction Technology Laboratories (CTL).

Phase 2: Laboratory demonstration tests of slab track. Phase 2 demonstrated the ability of 

DFST and IDBT in a laboratory environment to pass the stress and fatigue tests required for 

39-ton axle loads (Ball, 2004). Phase 2 was completed by CTL.

Phase 3: Field slab track demonstration tests from July 2003 to July 2006. Tests were 

funded primarily by FRA and conducted at TTC in Pueblo, Colorado, by TTCI. Phase 3 was 

completed by PCA, FRA, and TTCI. 

This report summarizes the results and findings of Phase 3.
6

1.2 Objective

An extensive slab track testing program was designed and started in July 2003 on the HTL at the 

TTC’s FAST. The target tonnage for the 3-year testing program was 150 MGT, but the actual 

accumulated total tonnage at the end of July 2006 was 170 MGT. During the 3 yr of testing and 

monitoring, various measurements were conducted to demonstrate the durability of the slab track 

for 39-ton axle loads while maintaining the track geometry conditions of a Class 9 track. More 

specifically, the testing program was designed to:

 Quantify slab track performance

 Quantify the actual load environment and the corresponding vibration behavior of the 

slab track

 Quantify stress and deformation behaviors of individual slab track and subgrade 

components

 Quantify slab track stiffness characteristics

As part of the slab track demonstration and testing program, the project was also intended to: 

 Demonstrate that a slab track can be built to HSR track tolerances (Class 9 track)

 Validate the slab track design procedures developed in Phase 1 and the laboratory 

tests completed in Phase 2 (this task was completed by PCA and CTL)

1.3 Approach

The testing program was designed to achieve the previously stated objectives and included static 

and dynamic measurements and both short- and long-term monitoring. Some measurements 

were conducted using onboard transducers on test vehicles while other measurements were 

performed using transducers installed in the slab track (wayside transducers). The following is a 

list of measurements and monitoring conducted throughout the testing program:

 Track geometry and track geometry change over time

 Vertical track modulus and stiffness

 Lateral track gage strength

 Dynamic vehicle/track interaction in terms of wheel/rail forces measured via 

instrumented wheelsets (IWS)

 Vertical and lateral rail forces measured using wayside load station

 Rail-to-slab vertical and lateral deflections

 Vertical deformation in slab, subbase, and subgrade
7

 Subgrade pressure

 Vibration attenuation from rail to slab

 Rail bending strain, strains of slab surface, and steel reinforcement bars

 Maintenance records

1.4 Scope

The slab track test section in the HTL is in a 5-degree curve with 4-inch superelevation. The 

total slab track section is 500 ft long, including 250 ft of the IDBT and 250 ft of the DFST. The 

transition from each slab track to the ballasted track is in a spiral from the 5-degree curve to the 

tangent. 

Although the 500-foot slab track test section was designed, constructed, and maintained as 

Class 9 track, the transitions and the rest of the HTL are Class 4 track. The slab track test section 

represented a track condition considered severe for Class 9 track because Class 9 track would 

generally not be built in a 5-degree curve and its proximity to Class 4 track was a factor. In 

addition, a 36-ton axle load is considered HAL in revenue service on North American railroads 

whereas the nominal axle load of the train operating on the HTL at FAST is 39 tons. Although 

not the focus of this testing, performance of fasteners was examined as necessary for slab track. 

In this report, the results, discussions, and conclusions presented are based on the testing of the 

slab track for the duration of 3 yr (July 2003–July 2006) and for a total accumulated traffic of 

170 MGT. At the time of this writing, the slab will remain in track until a reason to remove it 

develops, such as new testing space needs, operational safety, or another concern or need 

develops.
8

2. Design and Construction of Slab Track Test Section

2.1 HTL and Load Environment

2.1.1 HTL and Section 38

The HTL is located at FAST and is one of the several tracks used at TTC for advanced testing. 

Figure 1 shows the HTL and other test tracks at TTC.

Figure 1. Test Tracks at TTC

The HTL is a test loop 2.7 mi long and is used primarily for track component reliability, wear, 

and fatigue research under HAL traffic. As Figure 2 shows, the HTL is divided into test 

sections, which generally correspond to tangents, spirals, curves (three 5-degree curves and one

6-degree curve), and turnouts. Several experiments are currently being conducted in this loop, 

such as rail performance, weld performance, evaluation of ties and fasteners, frogs, turnouts, 

ballast, and subgrade. 

The slab track test section has a 5-degree curve with 4-inch superelevation and is located in the 

bypass track in Section 38. Section 38 is approximately 510 ft long. Section 37 and Section 39 

are adjacent to Section 38 and are in spirals to the tangents. The two transitions from the slab to 

the ballasted track are located in these two spirals. Note, Section 31 and Section 7 of the HTL 

have the same curvature and superelevation as Section 38 and are used for comparisons as

ballasted track with Section 38, including the slab track. As ballasted track, Section 31 has 

mixed concrete and wood ties whereas Section 7 has only wood ties.
9

3

37

38

39

40

41

2

1

33

32

31

30

28 27

26

25

23 24

9

8

7

6

5

4

36

29

35

2

8

B

35 B

Figure 2. Tonnage Loop (Slab Track in Section 38)

2.1.2 Operation and Load Environment at FAST

Figure 3 shows the test train at FAST running through the slab track test section on the HTL. 

The train at FAST generally consisted of three or four locomotives and 60–80 loaded freight 

cars. Each car weighed 315,000 lb. The nominal axle load of the freight cars is 39 tons, whereas 

the nominal axle load of the locomotives is 32 tons. Axle spacing is 72 in for the freight cars and 

108 in for the locomotives. The train runs at a nominal speed of 40 mph and generally operates 

from late night to early morning of the next day, accumulating approximately 1 MGT each night. 

The lapse time between the last freight car and the first locomotive is roughly 2.3 min. 

Depending on the annual operating budget provided by the AAR and FRA, trains at FAST 

generate 100–150 MGT per year, with roughly a 50/50 split between traffic on the mainline and 

the bypass during the 3 yr of the slab track testing program (July 2003–July 2006). Additionally, 

the traffic at FAST is scheduled such that approximately 50 percent is accumulated with the train 

running CW, while the other 50 percent is accumulated with the train running CCW.

In addition to the HAL trains at FAST, short test trains (consists) are often put together with 

several HAL freight cars and an instrumentation coach car. These short test trains are intended 

for various testing purposes and experiments within the FAST program.
10

Figure 3. FAST HAL Train Running on the HTL

Figure 4 shows the distributions of vertical and lateral wheel loads recorded in the HTL by using 

IWS installed under a freight car at FAST. Figure 5 shows the results recorded for Section 38.

These results were recorded before the slab track was built into this section. Section 5 describes 

how the IWS technology is used to measure wheel and rail forces. The results shown in Figure 4

and Figure 5 were obtained at 40 mph in both the CW and CCW directions and were part of the 

load environment data provided to PCA and CTL for analysis and design of the slab track test 

section in the HTL. 

The distributions of wheel loads shown in these two figures provide a range of wheel loads—the 

maximum and minimum wheel loads that are generated under 39-ton axle loads. For example, in 

Section 38, vertical wheel loads varied between 15 and 70 kip, while lateral wheel loads varied 

between -5 and 30 kip. More importantly, these distribution results indicate how often each load 

level would occur in the HTL or Section 38. For example, in Section 38, when the train operated

in the CW direction, the median vertical wheel load on the high rail (outside rail) was 43 kip 

while the medium vertical wheel load on the low rail (inside rail) was 35 kip. Note, at 40 mph 

with 4-inch superelevation, Section 38 has a 2-inch underbalanced condition, meaning more 

vertical load would be carried on the high rail than on the low rail.
11

Figure 4. Distribution of Vertical and Lateral Wheel Loads in the HTL

Figure 5. Distribution of Vertical and Lateral Wheel Loads in Section 38

Vertical Force - HTL Loop

40mph, CW

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

10 20 30 40 50 60 70

Vertical (kips)

Cummulative Percent

Leading Axle - Inside Rail Leading Axle - Outside Rail

Vertical Force - HTL Loop

40mph, CCW

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

10 20 30 40 50 60 70

Vertical (kips)

Cummulative Percent

Leading Axle - Outside Rail Leading Axle - Inside Rail

Lateral Force - HTL Loop

40mph, CW

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-5 0 5 10 15 20 25 30

Lateral (kips)

Cummulative Percent

Leading Axle - Inside Rail Leading Axle - Outside Rail

Lateral Force - HTL Loop

40mph, CCW

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-5 0 5 10 15 20 25 30

Lateral (kips)

Cummulative Percent

Leading Axle - Outside Rail Leading Axle - Inside Rail

Figure 5

Vertical Force - Section 38

40mph, CW

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

10 20 30 40 50 60 70

Vertical (kips)

Cummulative Percent

Leading Axle - Inside Rail Leading Axle - Outside Rail

Vertical Force - Section 38

40mph, CCW

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

10 20 30 40 50 60 70

Vertical (kips)

Cummulative Percent

Leading Axle - Outside Rail Leading Axle - Inside Rail

Lateral Force - Section 38

40mph, CW

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-5 0 5 10 15 20 25 30

Lateral (kips)

Cummulative Percent

Leading Axle - Inside Rail Leading Axle - Outside Rail

Lateral Force - Section 38

40mph, CCW

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

-5 0 5 10 15 20 25 30

Lateral (kips)

Cummulative Percent

Leading Axle - Outside Rail Leading Axle - Inside Rail
12

2.2 Design and Construction of Slab Track Test Section

Although the focus of this report is on the performance testing of the slab track, this section gives 

a description of the design and construction of the slab track in the HTL. Additional information 

about the design and construction of the slab track can be found in the following references: 

 Kucera et al., 2003

 Lotfi and Oesterle, 2005

 Bilow and Li, 2005

2.2.1 Slab Track Design and Construction

PCA and CTL (Lotfi and Oesterle, 2005) completed the design of the slab track test section, 

including structural analysis, concrete mix design, slab profile, and reinforcing design. TTCI 

designed the actual layout of the test section based on the existing alignment and grade 

conditions of Section 38. 

Figure 6 shows the overall plan view of the slab track test section in the HTL. As shown, this 

test section is located in Section 38 (bypass) and includes 250 ft of the IDBT slab track and 

250 ft of the DFST slab track. The 250-foot length for each slab was regarded as sufficient to 

ensure that the wayside instrumentation (Sections 5–9) located near the middle of each slab 

would not be impacted by the effect of adjacent ballasted tracks. As mentioned earlier, Section 

38 is a 5-degree curve and has a 4-inch superelevation. At the end of the IDBT and the DFST, a 

25-foot transition zone was installed between the slab track and the existing ballasted track. 

Figure 6 also shows the typical cross-sections of the DFST and the IDBT. The rails are fastened 

directly to the slab on the DFST, which is supported on a 6-inch layer of soil cement1subbase 

and the underlying subgrade. The rails are supported by two independent block ties on the IDBT 

that are supported by the slab, the soil cement subbase, and the subgrade. The Amtrak 

Construction Standards for Class 9 Track (with an allowable speed of 200 mph) were used for 

the construction of the slab track test section. More specifically, the following tolerances were

used for the construction of the slab track in the HTL:

 Surface limit (deviation at midordinate of 62-foot chord) 1/8 in

 Deviation in crosslevel 1/8 in

 Alignment limit (deviation at midordinate of 62-foot 

chord)

1/8 in

 Gage limit +1/16–3/32 in

 

1

See Subbase for a definition of soil cement.
13

To meet the tight construction tolerances, a top-down construction method was used for the 

installation of the slab track test section. The top-down construction procedure requires 

establishing the accurate position (alignment, gage, surface, and crosslevel) of the rails to the 

tolerances listed above, then building the rest of the track from the rails down to the fastening 

and to the casting of the reinforced concrete slab on the prebuilt soil cement subbase and 

subgrade. In the succeeding sections, descriptions are given regarding how each component of 

the slab track, including subgrade, subbase, IDBT, and DFST concrete slab were built. 

Additional information can be found in a paper by Kucera et al. (2003).
14

Figure 6. Slab Track Plan and Details
15

2.2.2 Subgrade

To prepare for the slab track construction, the existing ballasted track was removed. The 

subgrade was then graded to the proper line and elevation. The subgrade soil consists of silty 

sand (PI = 5.9, LL = 18.5). Soil moisture content varied between 5 and 12 percent. The surface 

of the subgrade was recompacted at an optimum moisture content of 10.5 percent. The modulus 

of the soil was above 10,000 psi with compressive strength above 50 psi. The subgrade soil was 

considered as strong as track foundation support. Figure 7 shows the final prepared subgrade 

surface. Note, from the IDBT to the DFST, the subgrade has a slight downhill grade 

(0.4 percent).

Figure 7. Subgrade Surface for Slab Track Test Section

2.2.3 Subbase

The subbase is a 6-inch soil cement layer. This layer was installed by mixing 5 percent of 

cement (based on soil weight) with the soil from the borrow area (the same silty sand) and was 

compacted at an optimum moisture content of 12.5 percent. Compaction was specified to be 

98 percent of the maximum (modified Proctor), with the maximum being 118 pounds per cubic 

foot (pcf). The target compressive strength was 700 psi, with subsequent cores showing actual 

strength between 780 and 840 psi. Figure 8 shows several pictures of the construction of the test 

section and the final surface of the soil cement layer.
16

Figure 8. Soil Cement Subbase Surface for Slab Track Test Section
17

2.2.4 Direct Fixation Slab Track

Figure 9 illustrates the plan and details of the DFST test section. The concrete slab is 1 ft thick, 

10 ft 6 in wide, and built with 5,000 psi strength concrete. The Acoustic Loadmaster DF 

fasteners, manufactured by Advanced Track Products, Inc., are spaced at 2-foot intervals and are 

used to anchor the rails to the slab by four anchor bolts. For the DFST, track resilience and 

damping are provided primarily through the rubber pads installed between the fastener plates and 

the slab surface. As a reference, the laboratory test at CTL (Ball, 2004) showed 0.22 in of 

deflection under 39-kilopound vertical load, resulting from pad deformation.

Figure 9. DFST Plan and Details
18

Figure 10 shows construction of the DFST. As shown, the reinforced concrete was cast in place 

with the rails and fasteners already established in position, using the top-down construction 

method. The positions of the rails were set up using a fixture known as the iron horse, used to 

support the rails and fasteners and adjusted to obtain proper surface, alignment, crosslevel, and 

gage of the rails. The iron horse fixtures were provided by Amtrak and are shown being spaced 

at 10-foot intervals along the track in Figure 10.

Note, before the construction of the DFST, the rails were painted white to reduce the effect of 

sunlight on the rail temperature. This practice, however, was not followed later during the 

construction of the IDBT.

Figure 10. Construction of DFST Using Top-down Method

2.2.5 Independent Dual Block Track

Figure 11 shows the plan and details of the IDBT test section. The IDBT, also known as low 

vibration track (LVT), consists of a 7.75-inch-thick reinforced bottom concrete slab (Phase 1

slab) 10 ft 6 in wide and built with 5,000 psi strength concrete, two independent block ties, and a 

self-compacting, unreinforced concrete slab (Phase 2 slab). The IDBT block ties were supplied 

by Permanent Way Corporation. The rails were fastened to the block ties using a fastening 

system provided by Sonneville International Corporation. For the IDBT, track resilience and 

damping were provided primarily through the rubber boots as well as the pads installed inside 

rubber boots. For reference, the laboratory test in CTL (Ball, 2004) showed 0.16 in of deflection 

under a 39-kilopound vertical load due mainly to the rubber boot and pad deformation.
19

Figure 11. IDBT Plan and Details

To construct the IDBT test section, the reinforced base slab (Phase 1 slab) was cast first. Then 

the precast block ties fitted with rubber boots and pads were set in place above the bottom slab 

together with the fastenings and the rails using the iron horse fixtures. The self-compacting 

concrete (Phase 2 slab) was poured around the block ties. Figure 12 shows the construction of 

the IDBT.
20

Figure 12. Construction of the IDBT Using Top-down Method

2.2.6 Transitions

The IDBT and DFST slab track sections were connected directly and their interface was detailed 

to provide continuous steel reinforcement. Figure 13 shows the interface plan and details 

between the IDBT and the DFST.

Figure 13. IDBT and DFST Interface Plan and Details
21

To accommodate the difference in track modulus between the slab track and the adjacent 

ballasted track, a 25-foot-long transition zone was designed and built. The transition was 

designed to have a 1-foot-thick reinforced concrete slab with upturned curbs to retain the ballast, 

a 12-inch ballast layer, and concrete ties. Figure 14 shows the plan and details of the DFST 

transition design (note, the IDBT has the same transition design as the DFST).

Figure 14. DFST Transition Design

Figure 15 shows the 25-foot base slab built in the transition to the IDBT test section and the final 

view of the transition track to the DFST test section. Note, from the end of each slab (IDBT or 

DFST), there are 18 concrete ties (over a distance of 36 ft) with Pandrol clips before all ties 

become wood ties in either Section 37 or Section 38. 
22

Figure 15. Base Slab in Transition to the IDBT and DFST Transition

2.2.7 Rail

The rails installed on the slab track test section were new 136 RE rails. They were installed as 

continuous welded rails. This was accomplished by welding (thermite welds) 80-foot rails. 

Altogether, there were 14 field welds in the slab track test Section 38. 

2.2.8 Completion of Slab Track Construction

The construction of the 500-foot slab track test section in the HTL was completed on July 22, 

2003. The slab track was built within Amtrak’s Class 9 track construction tolerances, with one 

exception: alignment toward the end of the DFST slab exceeded the allowable limit of 0.5 in for 

Class 9 track. Further discussion of this is continued in Alignment.

Because the slab track was built, it has been maintained in compliance with FRA’s Class 9 track 

safety standards. Note, the adjacent ballasted track and transitions were built and are maintained 

in compliance with FRA’s Class 4 track safety standards. Table 1 lists the completion of the 

major milestones for the slab track construction. Figure 16 shows the final views of the two slab 

tracks following their construction in Section 38.

Table 1. Milestones of Slab Track Construction

Task Date in 2003 Completed

Existing track removal April 14

Subgrade preparation April 15–24

Soil cement subbase April 24

IDBT Phase 1 concrete May 14

IDBT and DFST transition slab May 16–23

DFST slab June 13

IDBT Phase 2 concrete June 30

Final rail welding July 22
23

Figure 16. Views of IDBT (top) and DFST (bottom) following Construction
24

2.3 Design and Construction

2.3.1 Design

Adequate design and proper construction procedures are critical to the success of any DFST 

project. Direct fixation track is structurally more complex than traditional ballasted track, 

therefore, making the direct fixation system more sensitive to variations in subgrade and 

substructure. Neither ballasted track nor direct fixation track can bridge voids or subgrade 

support variations because of natural geological variations. Whereas ballasted track allows 

railroad engineers to repair structurally inadequate track sections during maintenance, direct 

fixation systems must be designed and constructed to accommodate local variations in track 

support conditions. This will ensure adequate long-term performance and attain the main benefit 

of direct fixation track: reducing future maintenance costs.

Reduced life-cycle costs for direct fixation track structures necessarily rely on knowledge of 

local geology and subgrade properties to ensure proper design for adequate long-term 

performance. The site investigation defines the subgrade properties and variability. These 

variations must be accounted for during design of the structural cross section, including concrete 

thickness and reinforcing steel details. The same information is required to achieve a structurally 

adequate ballasted track design using the AAR design procedure. This expense should,

therefore, not increase the cost of a direct fixation project over ballasted track. The one 

exception is where state of practice design procedures is not utilized and the age-old process is 

used to construct track regardless of site conditions using standard ballast and subballast 

thicknesses. In this case, the small design savings are far offset by the large maintenance costs 

required to repair structurally inadequate track sections. 

Uniform track support conditions are often difficult to achieve. Engineers use various 

construction and soil stabilization methods to improve the shallow subgrade soil properties and 

reduce the variability often associated with the subgrade surface as completed for the 

construction of the test section. The specific details for any subgrade improvement method will 

be site-specific but should be utilized for both direct fixation and ballasted track.

2.3.2 Construction Challenges

Construction of DFST for high-speed applications is a challenge due to the required tight 

tolerances on the order of 1/8 in. Construction processes to achieve such tight tolerances are 

complicated by environmental changes such as temperature, precipitation, humidity, and blown 

debris. Several studies have shown improved methods of constructing slab for transportation 

applications such as slipform paving. Because of the short test section that was built, this 

specialized construction procedure was not used.

Expansion and contraction of the rail due to temperature changes is an impediment to the 

construction of direct fixation track for high-speed applications. Mitigation of rail thermal heat 

gain using a light-colored paint was attempted but was not adequately successful to be repeated 

during the construction process. Using the top-down construction process (previously described) 

made achieving Class 9 construction standards possible but still difficult. Bracing the iron 

horses is required to maintain rail position. Class 9 construction standards were generally 

achieved. One exception was at the end of the slab where the curvature of the track that 
25

extended beyond the end of the slab was modified shortly after construction to achieve Class 9 

standards. Adjustment of direct fixation track following construction can generally be made 

within small tolerances as allowed by the fasteners, but the degree of adjustment required during 

construction may not be available in direct fixation fasteners. 
26

3. Track Geometry Performance of Slab Track

3.1 Objective

From the inception of slab track performance testing and monitoring, track geometry condition 

has been one of the main performance parameters measured. The objective of track geometry 

measurements is to quantify and demonstrate whether the slab track test section can withstand 

39-ton axle load traffic while maintaining the track geometry conditions of a Class 9 track.

3.2 Tonnage Accumulation on Slab Track

The trains at FAST started to operate on the slab track on July 30, 2003. Figure 17 shows the 

tonnage accumulation history for the slab track test section. Over a period of 3 yr, a total of 

170 MGT was accumulated, exceeding the 150 MGT target originally set for the program. 

Because slab track performance monitoring includes how track geometry might degrade with

traffic, tonnage accumulation history is shown in Figure 17 before track geometry performance 

results are discussed.

8/1/2003 2/1/2004 8/1/2004 2/1/2005 8/1/2005 2/1/2006 8/1/2006 

Accumulated MGT

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

Figure 17. Tonnage Accumulation on Slab Track

3.3 Track Geometry Measurement Methods

Several measurement methods were used to monitor how the geometry of the slab track would 

change due to the HAL traffic. The following sections describe the measurement methods used.
27

3.3.1 Top-of-Rail Elevation Survey

Surface elevations of both rails were measured by using a digital level at every third fastener/tie 

location throughout the slab track test section and its transitions. Fastener and tie locations are 

numbered CCW at FAST on each HTL section. The slab track section is defined by the 

fastener/tie location numbers shown in Table 2.

Table 2. Slab Track Test Section Defined by Fastener/Tie Location Number

Begin-Section 38 Begin-DFST DFST-IDBT Interface End-IDBT End-Section 38

1 5 129/130 254 258

Top-of-rail (TOR) elevation surveys were performed at 0, 0.5, 2, 5, 9, 22, 62, and 169 MGT. 

Surveys were conducted more frequently during the early phase following the construction of the 

slab track than during the later phase of the testing program. As will be presented later in this 

section, the slab track test section (either DFST or IDBT) experienced less than a 0.3-inch 

elevation change over an accumulated traffic of 169 MGT. 

3.3.2 Slab Movement Survey

For each slab track, two reference points were fixed to the slab surface. The reference points 

were used to monitor how much the DFST and IDBT slabs would move from the beginning to 

the end of the testing program. The movements of the slabs were measured in terms of elevation 

change as well as lateral position change. The lateral position change was defined by the radial 

distance change of the reference points with respect to their permanent benchmarks installed in 

the field. 

3.3.3 Track Geometry Measurement System

TTCI’s track geometry measurement system (TGMS) was used to measure track geometry 

conditions of the slab track. This system is an inertia/laser-based noncontact measurement 

system purchased from Imagemap, Inc. The system has been used extensively on the test tracks 

at TTC as well as on revenue service tracks for various research and testing projects. The system 

is portable, which means it can be installed onto the trucks of various vehicles. At the early 

phase of the slab track project, this system was attached to an empty freight vehicle (tank car). 

Later, the system was moved and installed on TTCI’s track loading vehicle (TLV) 

(see Figure 18).
28

Figure 18. TTCI’s Track Geometry Measurement System 

Attached to an Empty Tank Car (left) and TTCI’s Track Loading Vehicle (right)

The TGMS measured track geometry conditions during track geometry testing as defined by the 

parameters, including the following (note, the abbreviation given for each parameter in 

parentheses):

 Curvature (TGCU)

 Superelevation (TGSE)

 Surface of left and right rails (TGSL, TGSR)

 Alignment of left and right rails (TGAL, TGAR)

 Crosslevel (TGXL)

 Gage (TGGI)

For the slab track testing, FRA’s Track Safety Standards were used to determine if the slab track 

test section (Class 9) and the adjacent transitions (Class 4) were in compliance with the 

standards.

3.3.4 Other Measurements

In addition to TOR, the slab movement determined by survey, and track geometry was obtained 

using hand-string midchord offset (MCO) measurement to determine track alignment.
29

3.4 Initial Track Geometry of Slab Track

3.4.1 Surface

Figure 19 shows the initial TOR elevation survey results for both rails in the test section. As 

illustrated, a 4-inch superelevation exists between the outside (high) and inside (low) rails. As 

mentioned in Subgrade, a slight downhill grade (0.4 percent) exists from the IDBT to the DFST. 

Figure 19 illustrates that the slab track test section (both the IDBT and the DFST) had a very 

smooth surface condition. In contrast, the surface condition in the transitions showed more 

variation. Initial TOR elevation results were used to calculate the settlement of the slab track test 

section by subtracting later TOR elevation survey results from the reference values.

0 MGT

Fastener #

300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40

Relative Elevation (in.)

5

10

15

20

25

30

35

40

Inside rail top

Outside rail top # 4 (DFST)

 # 254 (IDBT)

 # 129/130 (center)

Figure 19. Initial Rail Surface Elevation Results

Figure 20 shows the track surface conditions (surface of left and right rails as well as crosslevel) 

obtained with the TGMS. The data shown were obtained on December 1, 2003, although track 

geometry measurements were also taken on July 30, 2003, immediately following the 

construction of the IDBT. The data collected on July 30, 2003, were not shown because the 

newly applied white paint on the rails of the IDBT interfered with the laser signal of the TGMS, 

which caused noise in the recorded data. Nonetheless, between the measurements on July 30 and 

December 1, only a small amount of traffic (2 MGT) accumulated, as shown in Figure 17.

Figure 20 shows that the slab track test section had a very smooth surface and little crosslevel 

deviation, consistent with the results shown in Figure 19. The surface of the transitions, 

however, is not as smooth but is still well within the allowable limits shown in Table 3.
30

Distance (ft)

2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700

Cross-level (in.)

-1.0

-0.5

0.0

0.5

1.0

TGXL 

CCW Direction (Dec. 1, 2003)

2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700

Surface (in.)

-1.0

-0.5

0.0

0.5

1.0

TGSL 

TGSR 

DFST IDBT

Figure 20. Initial Track Surface via TGMS

Table 3. Allowable Track Geometry Limits Used in Slab Track Testing

Parameter Class 4 Class 9

Gage -0.5 in/+1.0 in -0.5 in/+0.75 in

Gage—rate of change (31 ft) 0.5 in

Alignment (62 ft MCO) ±1.5 in ±0.5 in

Surface (62 ft MCO) ±2.0 in ±0.75 in

Crosslevel ±1.25 in

Crosslevel variation (62 ft) ±1.75 in ±1.5 in
31

At or near the end of each slab (IDBT or DFST), track geometry deviation in terms of MCO 

often appeared at a larger magnitude than in the middle part of the slab track. This was due to 

the proximity of the Class 4 track and because a rougher spot in a transition within 62 ft would 

make the MCO data appear larger, solely because of the way that the data were calculated. 

3.4.2 Gage

Figure 21 shows the initial gage results for the slab track test section and the adjacent ballasted 

track. As illustrated, the initial track gage met the allowable limits shown in Table 3. There 

were no exceptions in wide or narrow gage or in excessive rate of change within 31 ft.

Distance (ft)

2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700

Gage (in.)

-1.0

-0.5

0.0

0.5

1.0

DFST IDBT

CCW Direction (Dec. 1, 2003)

Figure 21. Initial Track Gage via TGMS

3.4.3 Alignment

Figure 22 shows the initial alignment results for the slab track and the adjacent ballasted track 

along with the curvature measurement results. Near the end of the DFST, alignment deviation 

exceeded the allowable limit of 0.5 in for Class 9 track (Table 3). This misalignment was caused 

by a change of track from Class 9 to Class 4 and a change of track curvature from the DFST slab 

track (5 degrees) to the ballasted track in test Section 37 (spiral). This misalignment was later 

corrected and will be discussed in Alignment.
32

Distance (ft)

2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700

Curvature (deg.)

-6

-5

-4

-3

-2

-1

0

CCW Direction (Dec. 1, 2003)

2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700

Alignment (in.)

-1.0

-0.5

0.0

0.5

1.0

TGAL 

TGAR 

DFST IDBT

Figure 22. Initial Track Alignment via TGMS

3.5 Track Geometry Maintenance and Change over Time

3.5.1 Alignment

Figure 22 shows that because of the misalignment measured near the end of the DFST, the track 

in Section 37 (spiral) and a part of the DFST track were realigned on April 21, 2004, using 

TTCI’s production tamper. To facilitate the alignment adjustment toward the end of the DFST, 

the bolts of 10 fasteners for both high and low rails were loosened. The slots of the DFST plates 

are such that they can allow some lateral movement of rails (roughly 0.5 in either way). The 

production tamper was then used to line the track from the ballasted track in test Section 37 to 

the DFST slab track by using the best fit as determined by the tamper.

Figure 23 shows the 62-foot-hand-string MCO results obtained just before the alignment work. 

As illustrated, the maximum MCO near the end of the DFST was approximately 5.88 in. 

Because the hand-string MCO data included the curvature component, a subtraction of 5 in

(MCO because of a 5-degree curve) in the DFST gives a maximum misalignment of 0.88 in. 

This is similar to the results shown in Figure 22 using the TGMS.
33

MCO Data Prior to Alignment Work (April 21, 2004)

Section # - Fastener #

sec 38-40sec 38-39sec 38-38sec 38-37sec 38-36sec 38-35sec 38-34sec 38-3sec 38-32sec 38-31sec 38-30sec 38-29sec 38-28sec 38-27sec 38-26sec 38-25sec 38-24sec 38-23sec 38-2sec 38-21sec 38-20sec 38-19sec 38-18sec 38-17sec 38-16sec 38-15sec 38-14sec 38-13sec 38-12sec 38-11sec 38-10

sec 38-9sec 38-8sec 38-7sec 38-6sec 38-5sec 38-4sec 38-3sec 38-2sec 38-1

sec 37-182sec 37-181sec 37-180sec 37-179sec 37-178sec 37-17sec 37-176sec 37-175sec 37-174sec 37-173sec 37-172sec 37-171sec 37-170

2 ft4 ft6 ft8 ft

10 ft12 ft14 ft

62' MCO

4.00

4.25

4.50

4.75

5.00

5.25

5.50

5.75

6.00

DFST Section 37

Figure 23. Hand-String MCO Data Showing Misalignment toward the End of the DFST

The hand-string MCO measurement was repeated after the alignment work. Figure 24 shows the 

measured results. The alignment work corrected the misalignment shown in Figure 22 and 

Figure 23. Immediately after the alignment work, the maximum alignment deviation was less 

than 0.2 in.

MCO Data Following Alignment Work (April 26, 2004)

Section # - Fastener #

sec 38-40sec 38-39sec 38-38sec 38-37sec 38-36sec 38-35sec 38-34sec 38-3sec 38-32sec 38-31sec 38-30sec 38-29sec 38-28sec 38-27sec 38-26sec 38-25sec 38-24sec 38-23sec 38-2sec 38-21sec 38-20sec 38-19sec 38-18sec 38-17sec 38-16sec 38-15sec 38-14sec 38-13sec 38-12sec 38-11sec 38-10

sec 38-9sec 38-8sec 38-7sec 38-6sec 38-5sec 38-4sec 38-3sec 38-2sec 38-1

sec 37-182sec 37-181sec 37-180sec 37-179sec 37-178sec 37-17sec 37-176sec 37-175sec 37-174sec 37-173sec 37-172sec 37-171sec 37-170

2 ft4 ft6 ft8 ft

10 ft12 ft14 ft

62' MCO

4.00

4.25

4.50

4.75

5.00

5.25

5.50

5.75

6.00

DFST Section 37

Figure 24. Hand-String MCO Data Showing Correction of Misalignment
34

After this adjustment on April 21, 2004, no further alignment work was done on the slab track. 

Nevertheless, alignment conditions toward the ends of the slab track (DFST and IDBT) degraded 

somewhat over time, due to more severe track conditions in the transition areas, such as the 

change of the Class 9 track to the Class 4 track and the change from a 5-degree curve to the 

spirals. 

Figure 25 shows the comparison of track alignments recorded on December 1, 2003, and May 

18, 2006 (at 162 MGT), just before the end of the testing program. For the slab track itself 

(DFST or IDBT), alignment changed very little. Alignment change or degradation, as mentioned 

above, occurred primarily at the transitions. The misalignment correction conducted on April 21, 

2004, caused the reduction of alignment deviation near the end of the DFST.

Because of the tough alignment transition and the way that MCO is calculated, higher 

magnitudes of alignment deviations can be seen at the ends of the DFST and IDBT, regardless of 

accumulated MGT. Nevertheless, both slab track types (DFST or IDBT) were able to maintain 

Class 9 alignment conditions throughout the testing program.

Distance (ft)

2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700

Alignment Right (in.)

-1.0

-0.5

0.0

0.5

1.0

CCW Direction

Alignment Left (in.)

-1.0

-0.5

0.0

0.5

1.0

Dec. 1, 2003

May 18, 2006

DFST IDBT

Figure 25. Change of Track Alignments over Time
35

Figure 26 shows the survey results obtained at 0 and 169 MGT, with the difference (delta) 

indicating lateral movements of the IDBT and DFST concrete slabs. As described earlier, four 

reference marks were set up on the surface of the concrete slabs, as shown in Figure 26. Lateral 

movement of each reference point was quantified by the distance change between a reference 

point and its permanent benchmark installed in the field. Very small lateral movements (less 

than 0.3 in) of the concrete slabs were recorded from the beginning to the end of the testing 

program.

Figure 26. Lateral (Radial) Movement of the IDBT and DFST Slabs

3.5.2 Gage

Figure 27 shows the comparison of gage test results from the beginning to the end of the test 

program. Only a small amount of gage degradation was on the slab tracks with most occurring at 

the ends. The allowable limits shown in Table 3 (wide gage, narrow gage, and rate of change) 

were not exceeded throughout the testing program. The test section never required gage 

correction during the test period.

Distance (ft)

2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700

Gage (in.)

-1.0

-0.5

0.0

0.5

1.0

Dec. 1, 2003

May 18, 2006

DFST IDBT

CCW Direction

Figure 27. Change of Track Gage over Time
36

3.5.3 Surface of Slab Track and Transitions

Figure 28 shows the comparison of surface test results from the beginning to the end of the 

testing program. As shown, the surface of the slab tracks (DFST and IDBT) is superior to that of 

the adjacent ballasted track. Larger deviations at the ends of the slabs were caused by the 

rougher track in transitions.

Distance (ft)

2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700

Right Surface (in.)

-1.0

-0.5

0.0

0.5

1.0

CCW Direction

Left Surface (in.)

-1.0

-0.5

0.0

0.5

1.0

Dec. 1, 2003

May 18, 2006

DFST IDBT

Figure 28. Change of Track Surface over Time

3.5.4 Cumulative Settlement of Slab Track and Transitions

During the testing program, the ballasted transitions to the slab tracks (IDBT and DFST) were 

given spot tamping and surfacing several times to smooth out the differential settlements 

accumulated between the slab track and the adjacent ballasted track.

To illustrate the differential settlement between the slab track and its transitions, Figure 29 shows 

the cumulative settlements measured from the TOR and their transitions. The settlement is 

calculated as the difference in TOR elevation taken between various MGT levels shown in each 

graph and the initial elevation data shown in Figure 19.

Before considering cumulative settlement results associated with the slab track (IDBT and 

DFST) and its adjacent transitions, one needs to realize that the absolute magnitudes of 

settlement at any MGT level and at any locations were small, as shown in Figure 29. The 

maximum settlement or rise of the slab track was less than 0.3 in, and the maximum settlement 

or rise of the ballasted transition track was only around 0.6 in. With respect to the allowable 

limits of track geometry surface parameters shown in Table 3, the magnitudes of the settlement 

shown in Figure 29 are of lesser significance as far as the safety allowance is concerned.
37

Within the above context, the following section describes spot tamping and surfacing work done 

in the transitions and discusses several issues related to the surface conditions of the slab track 

and transitions.

The slab track transitions experienced much larger settlement than the slab track. During the 

3 yr of the testing program, several spot tamping operations were performed to smooth out the 

differential settlement in the transition areas. In the transition of the DFST slab track, spot 

tamping work was performed twice with ballast added and the track actually lifted, a procedure 

called design-lift tamping. In the transition of the IDBT, this design-lift tamping procedure was 

never used; conventional spot tamping was performed several times.

The DFST settled roughly 0.1 in during the testing program. Almost all of the DFST settlement 

occurred within the first 0.5 MGT of traffic. This result could be anticipated as the track shakes 

down during construction. The relative uniformity of the initial settlement and lack of 

appreciable settlement after 0.5 MGT is indicative of quality foundation construction. The IDBT

actually rose 0.1–0.3 in, which was caused by fine sand that was gradually blown into the 

cavities between the IDBT tie blocks and cavities of the IDBT Phase 2 slab. Further discussion 

of this issue is provided in the next section.

In the last graph of Figure 29 (settlement at 169 MGT), the elevation changes of the four 

reference points installed on the slab surface are also shown. As illustrated, the vertical 

movement of the IDBT and DFST slabs was very small. It can be concluded that little settlement 

existed from the subbase and subgrade layers because the total settlement seen from the TOR or 

the slab surface was minor.
38

Settlement at 0.5 MGT

Fastener #

300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40

Settlement (in.)

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Inside rail surface

Outside rail surface

IDBT

DFST

Center

Settlement at 2 MGT

Fastener #

300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40

Settlement (in.)

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Inside rail

Outside rail

DFST

IDBT

 Center

Settlement at 5 MGT

Fastener #

300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40

Settlement (in.)

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Inside Rail

Outside Rail

Settlement at 9 MGT

Fastener #

300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40

Settlement (in.)

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

DFST

IDBT

 Center

Inside Rail

Outside Rail

Settlement at 62 MGT

Fastener #

300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40

Settlement (in.)

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Inside Rail

Outside Rail

 Center

IDBT

DFST

Settlement at 169 MGT

Fastener #

300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 -20 -40

Settlement (in.)

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Inside rail surface

Outside rail surface

Slab surface

 Center

DFST

IDBT

Figure 29. Cumulative TOR Settlement of Slab Track and Transitions
39

3.6 Other Observations about the Slab Track Test Section

The observations below are directly or indirectly related to track geometry performance of the 

slab track:

1. As mentioned in Rail, there were 14 field thermite welds in the slab track test section. 

None failed during the testing program for a total of 170 MGT as compared with the 

average life of 80 MGT for welds installed in similar 5-degree curves in the HTL.

2. There were no surface defects observed for the rails in the slab track test section. Rail 

wear due to 170 MGT of HAL traffic was insignificant. No corrugation development 

was observed.

3. On the basis of the feedback from train locomotive engineers at FAST, ride quality over 

the slab track test section was superior to that of the rest of the HTL. 

After a few million gross tons into the testing program, fine windblown sand and buildup of a 

gray material was observed around tie blocks on the IDBT slab surface. Figure 30 shows the 

fine sand deposit and gray material around the ties.

Figure 30. Fine Sand Deposit and Buildup of Gray Material around IDBT Tie Blocks

This buildup of gray material resulted from fine windblown sand gradually getting into the gaps 

of the IDBT components. Rainwater had direct access to the gaps as well. Under train 

operation, dirty water was observed flushing out of the boots following a rainfall. As a result, a 

gray material built up around block ties over time.

Although it was a gradual process, the fine sand deposited in the IDBT was considered to be the 

cause of the cumulative rise of TOR elevation of the IDBT, as Figure 29 indicates. The sand 

also caused an increase in track modulus (Figure 34) and a small change in dynamic rail 

deflection (refer to Figure 58) of the IDBT slab track during the 3 yr of testing. This issue will 

be discussed in Section 4 and Section 6.
40

4. Slab Track Stiffness Characterization

4.1 Introduction

One advantage of concrete slab track is that vertical and lateral track stiffness can be optimized 

by specifying elastomeric pad stiffness to match anticipated vehicle traffic. For this project, 

assuming a rather stiff subgrade, a finite element program was used to optimize slab element and 

pad stiffness for heavy freight loading (Lotfi and Oesterle, 2005). Characterization of slab track 

stiffness was accomplished through the measurements of vertical track modulus and lateral gage 

strength. Vertical track modulus or stiffness is an important property for a slab track. Track 

response behavior under dynamic wheel loads and its long-term performance is directly 

dependent on this property. 

The slab track test section in the HTL is built on a soil cement subbase and a firm subgrade as 

previously described in Section 2. As such, its resilience is derived from the rubber pads 

installed between rails and the slab (DFST) or from the rubber boots and pads between block ties 

and the slab (IDBT). One of the critical elements of the design process is to design a pad 

resilient enough vertically to spread the vehicle load over numerous fasteners, minimizing the 

load on individual components, yet stiff enough to control lateral movement of the rail and gage 

spreading. The design for this application resulted in a rather soft pad with relatively low 

vertical stiffness as seen in Figure 31. An area of concern was the amount of pad compression 

under full wheel load. Repetitive axle passes could result in elastomer heating and degradation 

of its load bearing/spreading characteristics. 

Measurement of lateral gage strength or stiffness can give a direct indication of lateral track 

response performance, particularly for the DFST, where resilient pads are used directly at the 

rail-slab interface. Although an elastic fastening system is always used in a slab track design, 

track gage spreading or lateral rail movement under dynamic wheel loading may be of concern 

with resilient pads. 

4.2 Vertical Track Modulus Testing

4.2.1 Test Methods

For a railroad track, track modulus is used as a measure of vertical stiffness of the rail foundation 

and is defined as the supporting force per unit length of rail per unit vertical deflection under a 

vertical load as determined by Equations 1 and 2 (Selig and Waters, 1994):

u = k4/3/(64EI)1/3 (1)

k = P/Y (2)

where u = track modulus (in the unit lb/in/in)

P = vertical wheel test load

Y = deflection
41

E = Young’s modulus of rail

I = moment of inertia of rail cross section

In Equations 1 and 2, the ratio of load over deflection (k) is known as track stiffness. Because of 

often nonlinear behavior of the load-deflection relationship, track modulus or the stiffness is 

often determined between two testing loads in terms of Equations 3 and 4 (Selig and Li, 1994):

u = ((P2-P1)/(y2-y1))4/3/(64EI)

1/3 (3)

k = (P2-P1)/(y2-y1) (4)

where P2 = heavy test load (often 40 kip)

P1 = seating test load (often 10 kip)

y2 = deflection under heavy test load

y1 = deflection under seating load

For the slab track test section in the HTL, vertical track modulus and stiffness were measured 

using two different methods: (1) static track modulus testing, and (2) in-motion track stiffness 

testing using TTCI’s TLV.

In a static track modulus test, static vertical wheel loads are applied on the rails, and the 

corresponding rail deflections (difference in elevation change for targets on the rails) are 

measured. Equations 3 and 4 are then used to calculate track modulus.

For in-motion track stiffness testing, a continuous track deflection profile is measured under a 

moving test load using TTCI’s TLV (Li et al., 2004). For a given constant vertical test load 

(e.g., 40 kip), lower track deflection indicates higher track stiffness. A continuous track 

deflection profile also gives an indication of how uniform or variable track stiffness is along a 

track. 

4.2.2 Test Results and Discussion

Figure 31 shows the test results of static track modulus for the entire slab track test section 

obtained at 2 MGT. During this test, track modulus measurements were taken at every sixth

tie/fastener location along the slab track. Track modulus was determined from the deflection 

measured between two test load levels (10 and 40 kip) as described above. 

As Figure 31 illustrates, track modulus was quite uniform for each of the IDBT and DFST slab 

tracks. For the IDBT, track modulus was about 3,000 lb/in/in, while for the DFST, track 

modulus was about 2,100 lb/in/in. These results were surprisingly lower than originally 

expected, especially for the DFST. It was expected that track modulus of the slab track test 

section would be much higher than 3,000–4,000 lb/in/in, which is the range for the ballasted 

track in the HTL. The original design intended to match the conventional track stiffness. An 
42

inaccurate estimate of subgrade/foundation modulus (Lotfi and Oesterle, 2005) resulted in the 

low as constructed track moduli. 

The test results shown in Figure 31 were independently verified by other measurements 

conducted at the same time, such as vertical track deflection test results under dynamic wheel

loads, and TLV in-motion track stiffness test results, presented in the following section.

Track Modulus at 2 MGT

Tie/Fastener #

260 240 220 200 180 160 140 120 100 80 60 40 20 0

Track Modulus (lb/in/in)

0

2000

4000

6000

8000

DFST

IDBT

 Center

Figure 31. Track Modulus Test Result of Slab Track (IDBT and DFST)

Figure 32 shows vertical track stiffness test results of in-motion testing, obtained by the TLV on 

December 8, 2003, at 2 MGT of traffic level. Figure 32 shows a continuous vertical track 

deflection profile along the slab track (Section 38) and the adjacent ballasted track in Section 37 

and Section 39, obtained under a constant wheel load of 40 kip. As illustrated, the DFST showed 

an average deflection of 0.2 in while the IDBT showed an average deflection of 0.15 in. The 

results shown in Figure 32 are consistent with the results shown in Figure 31—the DFST 

exhibited higher deflection or lower track modulus than the IDBT. Note, in this in-motion test, 

the consist was traveling in the CCW direction. As such, the results of the DFST appeared

before the test results of the IDBT. Also, the deflection results as shown come from offset-based 

measurements and are not the exact deflections generated under the test load (Li et al., 2004).

Figure 32 also shows that deflections generated in the DFST were higher than those in the 

adjacent ballasted track, indicating that the DFST was more resilient than the adjacent ballasted 

track. The IDBT presented track deflections (or track stiffness) similar to the adjacent ballasted 

track. Nevertheless, both slab tracks (DFST or IDBT) showed more uniform track stiffness than 

the adjacent ballasted track.
43

TLV In-motion Vertical Stiffness, CCW Direction, Dec. 8, 2003 (2 MGT)

Distance (ft)

600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 Vertcal Deflcetion @ 40 kips (in)

0.0

0.1

0.2

0.3

0.4

DFST

IDBT

Figure 32. In-motion TLV Track Stiffness Test Results

Figure 32 shows that immediately adjacent to the DFST or IDBT (the 25-foot transition area),

track deflections were significantly lower than those of the slab tracks or the ballasted track 

nearby. As described in Section 2, the 25-foot transition was built with a base slab underlying 

the ballast layer and included concrete tie; therefore, it should be much stiffer than the adjacent 

ballasted track. This is indicated by the test results shown in Figure 32.

The issue was that the design and installation of the 25-foot transitions did not achieve their 

objective in providing a gradual stiffness transition from the ballasted track to the stiffer slab 

track. Because the slab track was either more resilient than or equally resilient to the ballasted 

track, the installation of these two transitions became unnecessary at least in terms of track 

stiffness. 

Figure 33 shows the actual track modulus test results for the two 25-foot transition areas. As 

illustrated, these transition areas had average track moduli between 4,600 and 5,000 lb/in/in, 

significantly higher than the modulus of either slab track and also higher than the track modulus 

for the ballasted track on the HTL (3,000–4,000 lb/in/in).
44

Average Track Modulus at Transition (2 MGT)

Track Modulus (lb/in/in)

0

2000

4000

6000

8000

IDBT Transition DFST Transition

Figure 33. Track Modulus Test Result of Transition Track (IDBT and DFST)

Toward the end of the testing program at 169 MGT, static track modulus was measured again for 

the entire slab track test section. Because the test results from the first test indicated very 

uniform track stiffness along each slab track (IDBT or DFST), track modulus measurements 

were taken only at every 12th tie/fastener location during the second test.

Figure 34 shows the test results obtained at 169 MGT. For comparison purposes, the test results 

obtained at 2 MGT are also included in Figure 34. The track modulus for the IDBT increased 

noticeably. As compared with 3,000 lb/in/in measured at 2 MGT, track modulus of the IDBT 

measured at 169 MGT varied between 5,900 and 10,000 lb/in/in; this became an issue of concern 

because a track with a modulus higher than 10,000 lb/in/in may not be capable of 

accommodating large, dynamic vehicle-track interactions. Why did this increase occur? It was 

first considered that the measurements might be in error, but the analysis of the other test results 

and observations proved the validity of the track modulus test results of the IDBT at 169 MGT.

The track modulus test results measured for the DFST at 169 MGT showed an increase from that

measured at the beginning of the program (2 MGT). As compared with the early average of 

2,100 lb/in/in, track modulus measured at 169 MGT was 3,000 lb/in/in, which is nearly a 

50 percent increase in stiffness. A concern was that the elastomer stiffened and became more 

brittle, but no tests were performed to determine the stiffness. 

The test results shown in Figure 34 were also corroborated by the track vertical deflection results 

presented in Section 6. Under dynamic wheel loads, the magnitude of vertical deflections 

between the rail base and the concrete slab resulting from the rubber boots and pads decreased 

over time from the early test to the test conducted toward the end of the testing program.
45

Track Modulus at 169 MGT

Tie/Fastener #

260 240 220 200 180 160 140 120 100 80 60 40 20 0

Track Modulus (lb/in/in)

0

2000

4000

6000

8000

10000

12000

169 MGT (2006)

2 MGT (2003)

 Center

DFST

IDBT

Figure 34. Track Modulus Test Results of Slab Track (IDBT and DFST) at 169 MGT

As discussed in Section 3, a small but cumulative rise of the rail elevations was caused by fine 

windblown sand depositing in the space between the IDBT components. This process also 

would cause an increase in track modulus by limiting the deflection of the block ties within the 

rubber boots. The fine sand would also be flushed out with rainwater under train operation,

resulting in the gray material near the dual blocks noted during visual inspections. 

4.3 Gage Strength Testing

Lateral track gage strength testing was conducted several times throughout the testing program 

as part of track stiffness characterization testing for the slab track. Track gage strength is 

essentially the rail restraint capacity of ties and fasteners in maintaining proper track gage under 

wheel loads.

During a TLV gage strength test, constant 18-kilopound lateral and 33-kilopound vertical wheel 

loads are applied to each rail of the track (gage-spreading load). The collected data provide

information of unloaded gage, loaded gage, and delta gage (delta gage = loaded gage – unloaded 

gage). Unloaded track gage gives an indication of unloaded track geometry conditions, while 

loaded and delta gage characterize lateral gage strength or stiffness at the rail-tie interface 

provided by the fastening. In terms of delta gage, higher magnitudes would indicate lower gage

strength or lower gage stiffness. 

Figure 35 shows track gage strength test results obtained at 2 MGT, including unloaded gage, 

loaded gage, and delta gage. The maximum loaded track gage for the slab track was 

approximately 57 in. The unloaded gage test results were similar to those measured using 

TTCI’s TGMS (see Section 3.3.3). The delta gage results indicated more uniform lateral gage 

strength or stiffness for the IDBT and DFST than for the adjacent ballasted track. Between the 

DFST and IDBT, the former showed larger delta gage and indicated lower lateral track stiffness 
46

at the rail-fastener interface for the DFST. This was consistent with vertical track stiffness test 

results—for instance, the DFST also had lower vertical track stiffness than the IDBT. In 

addition, resilient rubber pads used in the DFST are installed at the rail-slab interface, which 

directly affects lateral gage strength or stiffness. On the other hand, resilient rubber boots/pads 

in the IDBT are installed at the tie block-slab interface, therefore, having less effect on the lateral 

gage strength or stiffness.

The DFST also showed larger gage spreading (lower gage stiffness) than the adjacent ballasted 

track. Again, this was consistent with the comparison of vertical track stiffness between the 

DFST and the adjacent ballasted track section. Therefore, in the case of the DFST, where 

vertical track stiffness is determined primarily by the elastic rubber pads, lateral gage strength is 

also determined by the stiffness characteristics of those pads. 

The IDBT showed delta gage similar to the adjacent slab track, although it was more uniform. In 

the case of the IDBT, rubber boots and pads were again installed between tie blocks and the 

concrete slab, which made gage strength less affected. Gage strength of the IDBT was mainly 

affected by the rail fastening system installed between rails and tie blocks (see Figure 11).
47

TLV Gage Strength, CCW Direction, Dec. 8, 2003 (2 MGT)

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600

Unloaded & Loaded Gage (in.)

56.0

56.5

57.0

57.5

58.0

Unloaded

Loaded

Distance (ft)

300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600

Delta Gage (in.)

0.0

0.2

0.4

0.6

0.8

DFST

IDBT

Figure 35. Track Gage Strength Test Results at 2 MGT

Two additional gage strength tests were conducted later in the testing program: one at 106 MGT 

and another at 169 MGT. Figure 36 shows the test results obtained at 169 MGT. Both DFST 

and IDBT showed more uniform lateral gage strength or stiffness than the adjacent ballasted 

track.

For the DFST, there was a significant increase of delta gage or decrease of lateral gage strength 

or stiffness. As compared with the test results obtained at 2 MGT, there was little increase in 

unloaded track gage, but there was a significant increase in loaded track gage. Compared with

the early 0.3 in of delta gage generated under the TLV test load (33 kip vertical and 18 kip 

lateral), delta gage increased to an average of 0.5 in (between 0.4 and 0.6 in) at 169 MGT. Note,

this increase was also observed to be 0.4 in during measurement at 106 MGT. This gradual 

decrease in gage strength seems to support the concern that the rubber pads used in the DFST 

might be too soft under 39-ton axle load operation. Under a gage spreading lateral wheel load, a 

rail supported on a soft pad would generally move more laterally than a rail supported on a stiff 

pad. However, the gage widening ratio (GWR) is within the allowed limit based on FRA’s 

Track Safety Standards for Class 9 track.
48

There was little increase in delta gage due to 169 MGT of traffic for the IDBT. Some change 

was noted in unloaded track gage. From 2 to 160 MGT, unloaded track gage increased from 

56.8 to 57.1 in. This slight increase was consistent with the gage change measured with the 

TGMS (Figure 27). Note that for the IDBT, the gage strength or stiffness is determined 

primarily by the elastic fastening system, which showed little degradation over time. The rubber 

boots and pads installed between tie blocks and the concrete slab would have little effect on the 

gage strength.

12300 12400 12500 12600 12700 12800 12900 13000 13100 13200 13300 13400 13500 13600

Loaded and Unloaded Gage (in.)

56.0

56.5

57.0

57.5

58.0

TLV Gage Strength, CCW Direction, June 16, 2006 (169 MGT)

Loaded

Unloaded

Distance (ft.)

12300 12400 12500 12600 12700 12800 12900 13000 13100 13200 13300 13400 13500 13600

Delta Gage (in.)

0.0

0.2

0.4

0.6

0.8

DFST

IDBT

Figure 36. Track Gage Strength Test Results at 169 MGT
49

5. Dynamic Wheel Load Measurements on Slab Track

5.1 Objective

One of the major measurements under the slab track testing program was that of dynamic wheel 

loads on the slab tracks as generated under train operations at FAST. Dynamic wheel loads were 

measured several times throughout the testing program to quantify slab track performance in 

terms of vehicle-track interaction and the load environment of the slab track test section.

Because of the superior track geometry of the slab tracks, dynamic vehicle track interaction 

levels were expected to be lower than those generated in the ballasted track sections in the HTL. 

It was necessary to quantify the slab track load environment to interpret slab track responses 

such as stress and deformation of slab track components. 

5.2 Test Methods

Dynamic wheel loads were measured using two different methods. One method involved the use 

of TTCI’s IWS, and the other involved the use of strain gage circuits installed on the rails 

(wayside load stations). The following section provides a brief description of each method. 

5.2.1 Instrumented Wheelsets

TTCI’s IWS technology was used every year as part of the testing program at FAST to measure 

wheel/rail forces for the entire HTL. An IWS can measure vertical and lateral wheel loads at 

wheel-rail contact points along the track while the test train runs at a given operating speed. 

During the IWS testing, data were collected at a sampling rate of 500 hertz (Hz) with an 

antialiasing low-pass filter at 100 Hz. For IWS testing on the HTL, data also included the signal 

of automated location detector (ALD) markers placed at various track locations to define and 

identify various test sections.

An IWS test often uses a short test train. For example, Figure 37 shows a short test train 

(consist) used in July–August 2003, immediately after the construction of the slab track test 

section. This short train was made up of a locomotive, an instrumentation coach, an empty tank 

car, and two HAL freight cars. The leading truck of the first freight car was equipped with a pair 

of IWS. The data acquisition system was housed in the instrumentation coach.
50

Figure 37. Short Test Consist including IWS (2003)

A major advantage of using an IWS is that it provides load measurements for the entire HTL, 

thereby providing test data for vehicle response comparison from section to section. In this 

section, IWS test results from several HTL sections, Section 7 and Section 31 (refer to Figure 2), 

are used for comparison between the slab track and the ballasted track sections of the same 

curvature and superelevation. 

5.2.2 Wayside Load Stations

In addition to using IWS technology, strain gages were installed on the rails to measure wheel 

loads generated on the slab tracks. For each slab track (IDBT and DFST), strain gages were 

installed on the high and low rails at the center of each slab and were calibrated to measure both 

vertical and lateral wheel loads. During each measurement, data were collected with each 

passing train. The sampling rate was 2,048 Hz with a 256-hertz low-pass filter.

Figure 38 shows the wayside load station installed at the center of the IDBT. As mentioned, the 

load stations were installed on both high and low rails; thus, four load stations were used for the 

slab track test section. During the testing program, wheel-rail forces were measured at three

different MGT levels: 

 0.6 MGT—July 30 and August 1, 2003

 65 MGT—January 24 and 25, 2005

 169 MGT—June 5 and 6, 2006

During each test, data were recorded under normal train operation at 40 mph. In addition, data 

were collected under the short test consist during the first test, conducted in July and 

August 2003.
51

Figure 38. Wayside Load Station

As with IWS data, wayside load station data were used to quantify slab track performance. 

Additionally, the data were used as the basis to interpret slab track responses such as stress and 

deformation, which were measured using the wayside transducers at the same locations. It was 

necessary to quantify the slab track load environment to understand slab track response. 

5.3 IWS Test Results

As mentioned, IWS testing was conducted annually from 2003 to 2005. No IWS testing was 

performed in 2006 under the FAST testing program before this report was prepared in 

August 2006. The actual IWS tests were conducted on the dates listed below; together with the 

measurements from the wayside load stations, they provided extensive results to achieve the 

objectives listed earlier.

 July 30, 2003 (0.6 MGT)

 July 16, 2004 (33 MGT)

 August 4, 2005 (117 MGT)

5.3.1 Vertical Wheel Load

Figure 39 shows the vertical wheel loads measured using IWS in July 2003 when the short test 

train ran over the slab track and the adjacent ballasted track. The results included the runs in 

both the CCW and CW directions on the HTL. In the CCW direction, the left wheel (VA 35) 

was on the low rail whereas the right wheel (VB 35) was on the high rail. In the CW direction, 

the left wheel was on the high rail and the right wheel was on the low rail.

As Figure 39 indicates, dynamic wheel loads varied throughout the slab track and the adjacent 

ballasted track due to car-body rocking action at 40 mph. Nevertheless, it is obvious that the slab 

track test section (either IDBT or DFST) showed lower magnitudes of dynamic forces than the 

adjacent ballasted track. In addition, the IWS data signals in the slab track test section were not 
52

as noisy as those in the adjacent ballasted track, indicating dynamic wheel loads with lower 

impact components (lower frequency responses).

Because the slab track test section is in a 5-degree curve with 4-inch superelevation, the average 

vertical wheel load was always higher on the high rail than on the low rail due to unbalanced 

speed at 40 mph.

CCW, 40 mph (A-left wheel, B-right wheel)

Distance (ft)

13000 13100 13200 13300 13400 13500 13600 13700 13800 13900 14000

Vertical Load (kips)

20

30

40

50

60

70 ALD

VA 35

VB 35

DFST IDBT

CW, 40 mph (A-left wheel, B-right wheel)

Distance (ft)

2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400

Vertical Load (kips)

20

30

40

50

60

70

ALD

VB 35

VA 35

IDBT DFST

Figure 39. Vertical Wheel Loads via IWS (2003)

Figure 40 shows the comparison of vertical wheel loads on the high rail in terms of statistical 

values (maximum, minimum, average, and standard deviation) between Section 38 (slab track) 

and Section 31 (ballasted track). As previously shown in Figure 2, Section 31 is the mainline 

track and is adjacent to Section 38. During the IWS testing conducted in July and August 2003, 

the test runs were on both the mainline track and the bypass track, thus providing data for direct 

comparison between Section 38 and Section 31, which have the same curvature and 

superelevation.

As Figure 40 shows, in either the CCW or the CW direction, the dynamic wheel loads (in terms 

of maximum, minimum, and standard deviation) were always higher on the ballasted track than 

on the slab track. Note that larger values of standard deviation, maximum, and the difference 

between maximum and minimum all correspond to larger dynamic wheel-track interactions.
53

Vertical Wheel Load (High Rail, 2003, CCW, 40 mph)

Section 31 Section 38

Kips

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75 Min 

Average 

Max 

StdDev 

Vertical Wheel Load (High Rail, 2003, CW, 40 mph)

Section 31 Section 38

Kips

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70 Min 

Average 

Max 

StdDev 

Figure 40. Section 38 (Slab Track) vs. Section 31 (Ballasted Track) Vertical Load in 2003

Similar test results were obtained in 2004 and 2005. For example, Figure 41 shows the 

comparison of vertical wheel loads between Section 38 (slab track) and Section 31 (ballasted 

track) from the tests conducted in 2004. Again, regardless of the direction of the test train 

operation on HTL, the dynamic wheel loads (in terms of maximum, minimum, and standard 

deviation) were always higher on the ballasted track than on the slab track.

In 2005, the IWS test was conducted on the HTL for a test train running only on the bypass. No 

IWS data were recorded for Section 31 on the mainline track. Figure 2 in Section 2 of this report

shows ballasted track in test Section 7 as having the same curvature and superelevation as that in 

Section 38. Therefore, a direct comparison was made between Section 38 and Section 7 

(Figure 42). Because an additional ALD marker was placed at the IDBT and DFST interface, the 

statistical values were obtained separately between the two slab tracks.

Again, for either slab track (IDBT or DFST), the vehicle-track interaction was lower on the slab 

track test section than on the ballasted track. For either train running direction, the ballasted 

track generated larger dynamic wheel loads than the slab track. No significant differences were 

observed between IDBT and DFST in terms of dynamic vertical wheel loads.
54

Vertical Wheel Load (High Rail, 2004, CCW, 40 mph)

Section 31 Section 38

Kips

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75 Min 

Average 

Max 

StdDev 

Vertical Wheel Load (High Rail, 2004, CW, 40 mph)

Section 31 Section 38

Kips

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70 Min 

Average 

Max 

StdDev 

Figure 41. Section 38 (Slab Track) Compared 

with Section 31 (Ballasted Track) Vertical Load in 2004

Vertical Wheel Load (High Rail, 2005, CCW, 40 mph)

Section7 DFST IDBT

Kips

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75 Min 

Average 

Max 

StdDev 

Vertical Wheel Load (High Rail, 2005, CW, 40 mph)

Section7 DFST IDBT

Kips

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70 Min 

Average 

Max 

StdDev 

Figure 42. Section 38 (Slab Track) Compared 

with Section 7 (Ballasted Track) Vertical Load in 2005
55

5.3.2 Lateral Wheel Load

Figure 43 shows the lateral wheel loads measured in 2003 using IWS when the test train ran over 

the slab track at 40 mph. The results on both the high and low rails are shown for the CCW and 

CW running directions of the test train. As expected, the high rail experienced higher lateral 

wheel loads than the low rail. The maximum lateral force was recorded in the CW direction and 

was about 20 kip. Adjacent to the slab track are spirals (Section 37 and Section 39) to the 

tangent track; therefore, lateral wheel loads decreased due to reduced curvature.

On the high rail, lateral wheel load varied from the minimum to the maximum, indicating 

significant dynamic lateral vehicle track interaction beyond just a constant steady vehicle curving 

action. In the case of only steady curving action, lateral wheel load appears to be more 

consistent through the body of a curve.

CCW, 40 mph (A-left wheel, B-right wheel)

Distance (ft)

13000 13100 13200 13300 13400 13500 13600 13700 13800 13900 14000

Lateral Load (kips)

-5

0

5

10

15

20

25

ALD

LA 35

LB 35

DFST IDBT

CW, 40 mph (A-left wheel, B-right wheel)

Distance (ft)

2400 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400

Lateral Load (kips)

-5

0

5

10

15

20

25

ALD

LB 35

LA 35

IDBT DFST

Figure 43. Lateral Wheel Loads via IWS (2003)

Figure 44 shows the comparison of lateral forces in terms of statistical values (minimum, 

average, maximum, and standard deviation) between Section 38 (slab track) and Section 31 

(ballasted track). Although not as significant, especially in the CW running direction of the test 

train, the slab track test section still generated lower dynamic lateral wheel loads than the 

ballasted track with the same curvature and superelevation.
56

Lateral Wheel Load (High Rail, 2003, CCW, 40 mph)

Section 31 Section 38

Kips

-5

0

5

10

15

20

25

30

Min 

Average 

Max 

StdDev 

Lateral Wheel Load (High Rail, 2003, CW, 40 mph)

Section 31 Section 38

Kips

-5

0

5

10

15

20

25

30 Min 

Average 

Max 

StdDev 

Figure 44. Section 38 (Slab Track) vs. Section 31 (Ballasted Track) Lateral Load in 2003

In the IWS tests conducted in 2004 and 2005, lateral forces measured on the high rail showed 

some significant lateral vehicle-track interaction at the transition areas, particularly when the test 

consist was exiting the slab track test section. 

Figure 45 shows the test results obtained in 2005 for the test train traveling at 40 mph in both 

directions. As illustrated, lateral forces in the slab track did not change much from the data 

collected in 2003; however, at the ends of the slab track, there was significant variation of lateral 

wheel load (mainly on the high rail). The maximum lateral wheel load was about 27 kip. The 

variation was even more obvious when the test consist was exiting the slab track, regardless of 

the running direction on the slab track.

Similar trends of lateral wheel load variation in the transitions were observed in the IWS test data 

obtained in 2004, although they were not as large as in the data collected in 2005. A careful 

examination of the test results obtained in 2003 (shown in Figure 43) also indicated larger lateral 

forces in the transition areas, especially at the exit transition.

Therefore, the misalignment and its growth in the transition areas (report Section 4) had a 

significant effect on lateral vehicle-track interaction and should be a track geometric parameter 

that requires extra attention.
57

CCW, 40 mph (A-left wheel, B-right wheel), 2005

Distance (ft)

11900 12000 12100 12200 12300 12400 12500 12600 12700 12800 12900

Lateral Load (kips)

-5

0

5

10

15

20

25 ALD

LA 35

LB 35

DFST IDBT

CW, 40 mph (A-left wheel, B-right wheel), 2005

Distance (ft)

1700 1800 1900 2000 2100 2200 2300 2400 2500 2600 2700

Lateral Load (kips)

0

10

20

30

ALD

LB 35

LA 35

IDBT DFST

Figure 45. Lateral Wheel Loads via IWS (2005)

5.4 Wayside Load Station Test Results

As described earlier, four wayside load stations were installed for the IDBT and DFST to 

measure vertical and lateral wheel loads on both the high and low rails located at the center of 

each slab. Unlike IWS load measurements along a track under the same wheels, the wayside 

load stations measure load variations at the same track locations due to passes of various axles.

5.4.1 Vertical Wheel Load

Figure 46 shows the vertical wheel loads measured under the short test consist (see Figure 37) in 

August 2003. The results were collected when the test consist was traveling at 40 mph in the 

CCW direction. As mentioned earlier, the train was made up of a locomotive, an instrumentation 

coach, an empty tank car, and two HAL freight cars. The vertical wheel loads recorded on both 

rails showed obvious variation of axle loads from vehicle to vehicle in this short test consist.

As expected, the vertical wheel load recorded on the high rail was higher than on the low rail due 

to unbalanced operating speed. The maximum dynamic vertical wheel load was 55 kip and was 

recorded at the IDBT load station. The maximum vertical wheel load recorded at the DFST load 

station was 47 kip.
58

DFST Vertical Force - 8/1/2003

CCW 40 mph, Short Consist

-10

0

10

20

30

40

50

60

8 9 10 11 12 13 14

Time (sec.) Force (kips)

High Rail Low Rail

IDBT Vertical Force - 8/1/2003

CCW 40 mph, Short Consist 

-10

0

10

20

30

40

50

60

12 13 14 15 16 17 18

Time (sec.) Force (kips)

High Rail Low Rail

Figure 46. Vertical Wheel Loads via Wayside 

Load Station (2003): Train Traveling in CCW Direction

Figure 47 shows the vertical wheel loads measured when the short test consist was traveling at 

40 mph in the CW direction. Again, the vertical wheel load recorded on the high rail was higher 

than on the low rail. The maximum dynamic vertical wheel load was 50 kip and was recorded at 

the DFST load station. The maximum vertical wheel load recorded at the IDBT load station was 

47 kip.

Note, the vertical wheel loads shown in Figure 46 and Figure 47 will be used to interpret 

dynamic track responses such as vertical deformation recorded under the same short test consist 

presented in later sections.
59

IDBT Vertical Forces - 8/1/2003

CW 40 mph, Short Consist

-10

0

10

20

30

40

50

60

10 11 12 13 14 15 16

Time (sec.) Force (kips)

High Rail Low Rail

DFST Vertical Forces - 8/1/2003

CW 40 mph, Short Consist

-10

0

10

20

30

40

50

60

14 15 16 17 18 19 20 21

Time (sec.) Force (kips)

High Rail Low Rail

Figure 47. Vertical Wheel Loads via Wayside 

Load Station (2003): Train Traveling in the CW Direction

The actual measurements under train operation at FAST were taken three times in July through 

August 2003 and once in January 2005 and June 2006. To deal with greater amounts of data 

generated under each train, the data were processed to get the statistical values (maximum, 

minimum, average, and standard deviation) from all peak values obtained under all train passes 

from each of the three tests.

Figure 48 shows the statistical results for all three tests conducted in three different years. All 

data were recorded when the trains at FAST were running in the CCW directions. As shown 

from 2003 to 2006, no obvious increase existed of vehicle-track interaction for the vertical loads 

recorded on both the high and low rails in terms of these statistical values for either the DFST or 

the IDBT.
60

DFST High Rail Vertical Forces

0

10

20

30

40

50

60

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Force (kips)

Min Avg Max Std Dev

DFST Low Rail Vertical Forces

0

10

20

30

40

50

60

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Force (kips)

Min Avg Max Std Dev

IDBT High Rail Vertical Forces

0

10

20

30

40

50

60

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Force (kips)

Min Avg Max Std Dev

IDBT Low Rail Vertical Forces

0

10

20

30

40

50

60

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Force (kips)

Min Avg Max Std Dev

Figure 48. Vertical Wheel Loads Recorded under FAST Trains from 2003 to 2006

5.4.2 Lateral Wheel Load

Figure 49 shows the lateral wheel loads measured under the short test consist on August 1, 2003. 

The results were obtained when the test consist was traveling at 40 mph in the CCW direction. 

The lateral wheel loads recorded on both rails showed variations due to change of axle loads 

from vehicle to vehicle. Generally, higher axle loads would generate higher lateral wheel loads. 

The leading axle of each truck also generated higher lateral wheel load than the trailing axle. 

Under this run, the maximum lateral wheel load was close to 16 kip, recorded on the high rail in 

the IDBT.
61

DFST Lateral Force - 8/1/2003

CCW 40 mph, Short Consist

-4

-2

0

2

4

6

8

10

12

14

16

8 9 10 11 12 13 14

Time (sec.) Force (kips)

High Rail Low Rail

IDBT Lateral Force - 8/1/2003

CCW 40 mph, Short Consist

-4

-2

0

2

4

6

8

10

12

14

16

12 13 14 15 16 17 18

Time (sec.) Force (kips)

High Rail Low Rail

Figure 49. Lateral Wheel Loads via Wayside 

Load Station (2003): Train Traveling in the CCW Direction

Figure 50 shows the lateral wheel load recorded when the test train was traveling at 40 mph in 

the CW direction. The maximum lateral wheel load was 13 kip, recorded on the high rail from 

the DFST and IDBT load stations. 

From the IWS test results (Figure 43 and Figure 45), lateral wheel loads generated on the high 

rail were generally higher than on the low rail. This was true in terms of wayside load station 

data shown in Figure 49 and Figure 50. However, a wayside load station measures lateral wheel 

loads only at a given track location; therefore, the difference in lateral wheel loads between the 

high and low rails may not be as large as that shown over the length of a given track segment. 
62

IDBT Lateral Forces - 8/1/2003

CW 40 mph, Short Consist

-4

-2

0

2

4

6

8

10

12

14

16

10 11 12 13 14 15 16

Time (sec.) Force (kips)

High Rail Low Rail

DFST Lateral Force - 8/1/2003

CW 40 mph, Short Consist

-4

-2

0

2

4

6

8

10

12

14

16

14 15 16 17 18 19 20 21

Time (sec.) Force (kips)

High Rail Low Rail

Figure 50. Lateral Wheel Loads via Wayside 

Load Station (2003): Train Traveling in CW Direction

Figure 49 and Figure 50 show the lateral wheel loads generated under the short test train. As 

mentioned, lateral wheel loads were also recorded every year under normal FAST train 

operation. For each FAST train pass, hundreds of axles passed by each load station. The data 

recorded were processed to obtain the statistical values (maximum, minimum, average, and 

standard deviation) from all peak values acquired under all train passes from each of the three 

tests.
63

Figure 51 shows the statistical results for all three tests conducted in 2003, 2005, and 2006. As 

shown, there was an increase of lateral wheel loads on both the high and low rails from the test 

conducted in 2003 to the one conducted in 2005. From 2005 to 2006, the trend was not quite 

obvious. As mentioned, lateral wheel loads on the low rail were generally lower than those on 

the high rail.

DFST High Rail Lateral Forces

0

4

8

12

16

20

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Force (kips)

Min Avg Max Std Dev

DFST Low Rail Lateral Forces

0

4

8

12

16

20

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Force (kips)

Min Avg Max Std Dev

IDBT High Rail Lateral Forces

0

4

8

12

16

20

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Force (kips)

Min Avg Max Std Dev

IDBT Low Rail Lateral Forces

0

4

8

12

16

20

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Force (kips)

Min Avg Max Std Dev

Figure 51. Lateral Wheel Loads Recorded under FAST Trains from 2003 to 2006

Finally, although test results are not presented in terms of single wheel, net axle, and truck side 

L/V ratios, no exceptions were in terms of vehicle-track interaction safety limits based on FRA’s 

Track Safety Standards for Class 9 track.
64

6. Deflection of Slab Track Components under HAL

This section presents test results of dynamic deflection responses of slab track components under 

HAL train operation. The slab track test section was instrumented to measure the following 

dynamic track responses:

 Vertical and lateral rail-to-slab deflections

 Vertical deformation of concrete slab, soil cement subbase, and subgrade

Dynamic deformation was expected to occur primarily between the rails and the concrete slab, 

with less deformation expected from the subbase and subgrade layers because of the resilience of 

the slab track test section that was provided mainly from the rubber pads (DFST) or the rubber 

boots/pads (IDBT) and the firm subbase layer and subgrade.

6.1 Instrumentation for Deformation Measurement

6.1.1 Linear Variable Differential Transformer for Rail-to-Slab Deflection

Field instrumentation was set up for measuring vertical and lateral rail deflections relative to the 

concrete slab. In the case of the DFST, rail-to-slab deflection essentially reflects the deformation 

due to direct-fixation rail fastenings and pads installed between the rail base and the concrete 

slab. In the case of the IDBT, rail-to-slab deflection reflects the deformation due to the rail 

fastening between the rail base and the block ties. More importantly, it reflects the deformation 

due to rubber boots and pads installed between the tie blocks and the concrete slab (Phase II slab 

for IDBT).

Linear variable differential transformers (LVDTs) were used to measure vertical and lateral railto-slab deflections under train operation. Like all other wayside transducers, rail-to-slab

deflection transducers (LVDTs) were used for both the high and low rails near the center of each 

slab (IDBT or DFST); however, because of the space required for each transducer, the wayside 

transducers were not all positioned in the same manner at the same locations. Figure 52 shows 

the actual layout of most wayside transducers for the IDBT (also for the DFST).

Figure 52. Layout of Wayside Transducers for IDBT (also for DFST)
65

Figure 53 shows the LVDT transducers installed on both the IDBT and the DFST to measure 

vertical and lateral rail-to-slab deflections under dynamic wheel loads. As shown, the reference 

plates were set up on the slab surface so that the deflection could be measured between the rail 

base and these references using LVDT transducers.

Similar to the wayside load stations, all wayside transducers including rail-to-slab deflection 

transducers used a sampling rate of 2,048 Hz with an antialiasing low-pass filter of 256 Hz.

Figure 53. LVDT for Vertical and Lateral Rail-to-Slab Deflection (IDBT and DFST)

6.1.2 Multidepth Deflectometers for Deformation in Slab, Subbase, and Subgrade

Multidepth deflectometers (MDD) were installed at four locations by CTLGroup technicians. 2 

These locations were near the high and low rails of the IDBT and DFST (see Figure 52 for

locations relative to other wayside transducers). For each location, a hole was drilled 10 ft deep 

through the concrete slab, subbase, and subgrade following the slab track construction. An

MDD fixture with four deformation transducers was installed in each hole to measure vertical 

deformation at four different depths.

Figure 54 shows the layout of four MDD transducers in each hole. These transducers were 

intended to measure vertical deformation under dynamic wheel loads at four different depths in 

the concrete slab layer, the subbase layer, and the subgrade. ML in this figure stands for 

measurement location. The depths of ML1 and ML3 were 5.8 and 2.8 ft, respectively. 

Figure 55 shows before-and-after installation views of the MDD fixtures.

 

2 CTL Group provided the MDD fixtures for the test. Information on the MDD measurement technique can be 

found at www.CTLgroup.com.
66

Figure 54. MDD for Vertical Deformation at Four Different Depths

Figure 55. MDD before and after Installation in Slab Track

6.2 Test Results

6.2.1 Vertical Rail-to-Slab Deflection

Figure 56 shows the test results of vertical rail-to-slab deflections for both DFST and IDBT as 

recorded under the short test train traveling at 40 mph in the CCW direction. As illustrated, 

larger vertical deflection was generated in the DFST (0.22 in on the high rail) than in the IDBT 

(0.15 in on the high rail), consistent with the track modulus and stiffness test results shown in 

Figure 31 and Figure 32 (also similar to the laboratory test results listed in Section 2.2.4 and 

Section 2.2.5). The more resilient DFST generated larger rail-to-slab deflection than the IDBT.

Slab

Subbase

Subgrade

Anchor
67

Both track stiffness and actual load environment need to be taken into account when interpreting 

deflection results. As a result of larger vertical wheel loads on the high rail than on the low rail, 

the deflection generated from the high rail was generally greater.

DFST Vertical Deflection - 8/1/2003

CCW 40 mph, Short Consist

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

8 9 10 11 12 13 14

Time (sec.)

Deflection (in.)

High Rail Low Rail

IDBT Vertical Deflection - 8/1/2003

CCW 40 mph, Short Consist

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

12 13 14 15 16 17 18

Time (sec.)

Deflection (in.)

High Rail Low Rail

Figure 56. Vertical Rail-to-Slab Deflection 

under Short Test Consist Traveling in the CCW Direction

The overlapping effects of two adjacent axles under each truck. For the vertical wheel loads 

shown in Figure 46 and Figure 47, axles under the same truck were essentially independent of 

each other in terms of dynamic wheel loads generated under each wheel. For the dynamic railto-slab deflection, most deflection did not return when the dynamic loading of the following 

wheel under the same truck occurred.
68

Figure 57 shows the vertical rail-to-slab deflection test results for both IDBT and DFST under 

the short test train when it was traveling in the CW direction. The trends of test results were 

similar to those recorded in the test run of the CCW direction (Figure 56); however, vertical rail 

deflections in DFST were larger (0.25 in) than those shown in Figure 56 (0.22 in). This was due 

to the higher generated vertical dynamic wheel loads when the short test train was traveling in 

the CW direction as shown in Figure 46 and Figure 47.

IDBT Vertical Deflection - 8/1/2003

CW 40 mph, Short Consist

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

10 11 12 13 14 15 16

Time (sec.)

Deflection (in.)

High Rail Low Rail

DFST Vertical Deflection - 8/1/2003

CW 40 mph, Short Consist

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

14 15 16 17 18 19 20 21

Time (sec.) Deflection (in.)

High Rail Low Rail

Figure 57. Vertical Rail-to-Slab Deflection 

under Short Test Consist Traveling in CW Direction
69

In addition to the measurements taken under the short test train in 2003, rail-to-slab deflections 

were measured under HAL train operations at FAST in the CCW direction. The dates listed 

below indicate when rail-to-slab deflections were measured. These dates were basically the same

as those for all other measurements obtained via the wayside load stations. 

 July 30 and August 1, 2003 (0.6 MGT)

 January 24 and 25, 2005 (65 MGT)

 June 5 and 6, 2006 (169 MGT)

Figure 58 shows the statistical results (minimum, average, maximum, and standard deviation) 

obtained from each of the three tests conducted from 2003 to 2006. The statistical values were 

based on the peak values corresponding to all passing wheels from each test conducted.

Again, the DFST exhibited larger vertical rail deflections than the IDBT. Only a minor increase 

of rail deflection for the high rail from 2003 to 2006 for the DFST was observed and even less 

for the low rail. The smaller deflection recorded on the low rail in January 2005 was due to 

lower dynamic vertical wheel loads (see Figure 48). Not only should track stiffness be taken into 

account but dynamic wheel loads should also be considered to interpret deflection results.

DFST High Rail Vertical Deflection

0.00

0.05

0.10

0.15

0.20

0.25

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Deflection (in.)

Min Avg Max Std Dev

DFST Low Rail Vertical Deflection

0.00

0.05

0.10

0.15

0.20

0.25

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Deflection (in.)

Min Avg Max Std Dev

IDBT High Rail Vertical Deflection

0.00

0.05

0.10

0.15

0.20

0.25

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Deflection (in.)

Min Avg Max Std Dev

IDBT Low Rail Vertical Deflection

0.00

0.05

0.10

0.15

0.20

0.25

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Deflection (in.)

Min Avg Max Std Dev

Figure 58. Vertical Rail-to-Slab Deflection under FAST Train (2003–2006)
70

For the IDBT, both the high and low rails showed a gradual decrease of vertical rail-to-slab

deflections, especially if taking into account the vertical wheel loads recorded at the same time 

(see Figure 48). This trend was consistent with the gradual increase in track modulus or track 

stiffness for the IDBT (refer to Section 4). 

6.2.2 Lateral Rail-to-Slab Deflection

Figure 59 shows the test results of lateral rail-to-slab deflections for both the DFST and the 

IDBT obtained under the short test train traveling at 40 mph in the CCW direction. The 

maximum lateral rail-to-slab deflection was close to 0.06 in for both the IDBT and the DFST. In 

general, the lateral deflections were larger on the high rails than on the low rails due to higher 

lateral rail forces generated. Again, to interpret lateral rail deflection results shown in Figure 59, 

the lateral wheel loads shown in Figure 49 need to be considered. For example, in the CCW run 

shown in this example, lateral wheel loads generated on the DFST were actually lower than those 

on the IDBT.

DFST Lateral Deflection - 8/1/2003

CCW 40 mph, Short Consist

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

8 9 10 11 12 13 14

Time (sec.)

Deflection (in.)

High Rail Low Rail

IDBT Lateral Deflection - 8/1/2003 CCW 40 mph, Short Consist

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

12 13 14 15 16 17 18

Time (sec.) Deflection (in.)

High Rail Low Rail

Figure 59. Lateral Rail-to-Slab Deflection 

under Short Test Consist Traveling in CCW Direction
71

Figure 60 shows the test results recorded when the short test train was traveling in the CW 

direction. The maximum lateral rail-to-slab deflection was 0.1 in for the DFST and close to 

0.08 in for the IDBT. Again, the lateral rail deflections generated on the high rail were larger 

than those on the low rail, reflecting higher lateral wheel loads on the high rail.

IDBT Lateral Deflection - 8/1/2003

CW 40 mph, Short Consist

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

10 11 12 13 14 15 16

Time (sec.)

Deflection (in.)

High Rail Low Rail

DFST Lateral Deflection - 8/1/2003

CW 40 mph, Short Consist

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

14 15 16 17 18 19 20 21

Time (sec.) Deflection (in.)

High Rail Low Rail

Figure 60. Lateral Rail-to-Slab Deflection 

under Short Test Consist Traveling in CW Direction

Figure 61 shows the statistical values of lateral rail-to-slab deflections obtained from the three 

tests conducted in 2003, 2005, and 2006. The statistical values were obtained from peak values 

corresponding to all passing wheels for the HAL trains at FAST, recorded in each of the three 

tests conducted.
72

The DFST again generated larger lateral rail-to-slab deflections than the IDBT. The high rail 

always exhibited larger deflection than the low rail for both tracks due to higher lateral wheel 

loads.

From 2003 to 2006, the general trends of lateral rail-to-slab deflection were increasing and 

appeared consistent with the trend of decreasing gage strength for the DFST (Section 4).

During that same period, the general trends of lateral rail-to-slab deflections were decreasing, 

particularly for the deflections measured on the high rail for the IDBT. As shown in Figure 58, 

these trends were consistent with those of vertical rail-to-slab track deflections.

DFST High Rail Lateral Deflection

0.00

0.02

0.04

0.06

0.08

0.10

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Deflection (in.)

Min Avg Max Std Dev

DFST Low Rail Lateral Deflection

0.00

0.02

0.04

0.06

0.08

0.10

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Deflection (in.)

Min Avg Max Std Dev

IDBT High Rail Lateral Deflection

0.00

0.02

0.04

0.06

0.08

0.10

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Deflection (in.)

Min Avg Max Std Dev

IDBT Low Rail Lateral Deflection

0.00

0.02

0.04

0.06

0.08

0.10

2 MGT 67 MGT 169 MGT

8/1/2003 1/28/2005 6/6/2006 Deflection (in.)

Min Avg Max Std Dev

Figure 61. Lateral Rail-to-Slab Deflection under FAST Train (2003–2006)

6.2.3 Vertical Deformation in Slab, Subbase, and Subgrade Layers

Although four locations were instrumented with MDD and each location had four transducers to 

measure deformation at four different depths, only a few MDD transducers performed properly 

(outputting data signals). Fortunately, those were enough to verify what was already known. 

Only small deformation occurred from the layers underneath the concrete slab.
73

Figure 62 shows the MDD data that were collected under the short test train traveling at 40 mph 

in the CCW direction. For the DFST, the MDD data included the subgrade deformation (ML3 in 

Figure 54, or approximately 2.8 ft from the subgrade surface) under both rails. For the IDBT, 

the MDD data included the subbase deformation under the low rail (inside rail) and the subgrade 

deformation at two depths (ML3 and ML1 in Figure 54, or 2.8 and 5.6 ft from the subgrade 

surface) under the high rail (outside rail).

As shown, under HAL wheel loads, the maximum deformation in the subbase and subgrade 

(2.8 ft) was less than 0.06 in while the subgrade deformation at a depth of 5.8 ft was only 0.01 in.

DFST MDD - 8/1/2003

CCW 40 mph, Short Consist 

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

7 8 9 10 11 12 13 14 15

Time (sec.)

Vertical Deformation (in.)

Subgrade ML3, Inside Rail Subgrade ML3, Outside Rail

IDBT MDD - 8/1/2003

CCW 40 mph, Short Consist

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

12 13 14 15 16 17 18 19

Time (sec.) Vertical Deformation (in.)

Subbase, Inside Rail Subgrade, ML3, Outside Rail Subgrade, ML1, Outside Rail

Figure 62. MDD Test Results under Short Test Train Traveling in CCW Direction
74

Figure 63 shows the MDD test results that were recorded when the short consist was traveling at 

40 mph in the CW direction. Again, vertical deformation of less than 0.06 in was in the subbase 

and subgrade at 2.8 ft and less than 0.01 in at the subgrade depth of 5.6 ft.

As discussed earlier, two adjacent wheels under each truck overlapped each other in terms of 

rail-to-slab deflection response. In terms of subbase and subgrade deformation—as Figure 62

and Figure 63 show—four adjacent wheels under two closely adjacent trucks can be considered 

as one load cycle, especially if all four axles have similar weights. 

IDBT MDD - 8/1/2003

CW 40 mph, Short Consist

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

10 11 12 13 14 15 16 17

Time (sec.)

Vertical Deformation (in.)

Subbase, Inside Rail Subgrade ML3, Outside Rail Subgrade ML1, Outside Rail

DFST MDD - 8/1/2003

CW 40 mph, Short Consist

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

14 15 16 17 18 19 20 21

Time (sec.)

Vertical Deformation (in.)

Subgrade ML3, Inside Rail Subgrade ML3, Outside Rail

Figure 63. MDD Test Results under Short Test Train Traveling in CW Direction
75

MDD data were also recorded as part of the wayside measurements conducted in 2003, 2005, 

and 2006. Little change was observed as far as subbase and subgrade deformation recorded from 

those MDD transducers that worked. For example, Figure 64 shows the MDD test results 

obtained in the subgrade at two different depths (2.8 and 5.6 ft) under the train operation at 

FAST in June 2006. As illustrated, less than 0.06 in was recorded at the subgrade depth of 2.8 ft

and less than 0.015 in, at 5.6 ft.

Figure 62 through Figure 64 show that, because of the insignificant deformation, no statistical 

analysis was performed for the test data collected under trains at FAST from 2003 to 2006.

IDBT High Rail MDD - 6/6/2006

CCW 40 mph, FAST Train

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

15 35 55 75 95

Time (sec.)

Vertical Deformation (in.)

Subgrade ML3 Subgrade ML1

Figure 64. Subgrade Deformation under FAST Train Traveling in CCW Direction
76

7. Subgrade Pressure under Slab Track

Subgrade pressure was measured under the slab track testing program to quantify the load 

distribution under the concrete slab and the soil cement subbase layer during HAL train 

operation. Pressure transmitted to the subgrade was expected to be well below the subgrade soil 

strength because of the rigid concrete slab and the stiff subbase layer. 

7.1 Subgrade Pressure Cell and Installation

Pressure cells made by Geokon (model 3500) were used for subgrade pressure measurements. 

For each type of slab track (IDBT or DFST), six pressure cells were installed at the central area 

of each slab. Figure 65 shows the general arrangements of six pressure cells on the subgrade 

surface. As illustrated, three cells were arranged across the track under a tie. The three other 

cells were arranged across the track in the crib (between fasteners). Figure 52 shows the relative 

positions of these six pressure cells with respect to other wayside transducers.

Figure 65. Arrangement of Subgrade Pressure Cells

To install a pressure cell on the subgrade surface, a hole was dug through the finished subbase 

soil cement layer following its final compaction. Silica sand was applied to the hole to provide a 

uniform bearing for the pressure cell. After the pressure cell was placed and positioned on the 

subgrade surface, more silica sand was applied to cover it. Finally, the track crew added newly 

mixed soil cement to the holes in a single layer, and a hand compactor was used to compact the 

soil cement above the pressure cell. Figure 66 illustrates the procedure of installing the subgrade 

pressure cells. 

Subgrade pressure data under HAL train operation were collected using the same data 

acquisition system as for other wayside transducers, the same data sampling rate of 2,048 Hz,

and the same antialiasing low-pass filter of 256 Hz.

Although subgrade pressure data were collected three times (in July through August 2003, 

January 2005, and October 2005), the data collected in 2005 was determined later that it could 

not be considered reliable because of significant drifting of pressure readings in some pressure 

cells.
77

Figure 66. Installation of Subgrade Pressure Cells

7.2 Test Results

Figure 67 shows the subgrade pressure test results under the short test consist traveling at 

40 mph. The data were obtained in both CCW and CW directions in August 2003. For the 

DFST and IDBT, three pressure transducers were installed under the tie and three others, under 

the crib.

As shown, the maximum subgrade pressure under HAL vehicles was 12 psi, recorded under the 

outside (high) rail in the IDBT. For the DFST, the maximum subgrade pressure was 11 psi, 

recorded under the inside (low) rail. Under this short consist, heavier axle loads generated larger 

subgrade pressures. Regardless, the maximum subgrade pressures generated under HAL traffic 

were well below the compressive strengths of the subgrade soil, which were above 50 psi.

The relatively low subgrade pressure with respect to soil strength explains the small amount of 

subgrade deformation. As with the deformation responses of the subgrade, four adjacent wheels 

under two closely adjacent trucks can be considered as one load cycle as far as subgrade pressure 

is concerned.
78

DFST Pressure Cells (Under Tie) - 8/1/2003

CCW 40 mph, Short Consist

-2

0

2

4

6

8

10

12

14

8 9 10 11 12 13 14

Time (sec.)

Subgrade Pressure (psi)

Inside Middle Outside

DFST Pressure Cells (Under Crib) - 8/1/2003

CCW 40 mph, Short Consist

-2

0

2

4

6

8

10

12

14

8 9 10 11 12 13 14

Time (sec.)

Subgrade Pressure (psi)

Inside Middle Outside

IDBT Pressure Cells (Under Tie) - 8/1/2003

CCW 40 mph, Short Consist

-2

0

2

4

6

8

10

12

14

12 13 14 15 16 17 18

Time (sec.)

Subgrade Pressure (psi)

Inside Middle Outside

IDBT Pressure Cells (Under Crib) - 8/1/2003

CCW 40 mph, Short Consist

-2

0

2

4

6

8

10

12

14

12 13 14 15 16 17 18

Time (sec.)

Subgrade Pressure (psi)

Inside Middle Outside

DFST Pressure Cells (Under Tie) - 8/1/2003 CW 40 mph, Short Consist

-2

0

2

4

6

8

10

12

14

14 15 16 17 18 19 20 21

Time (sec.)

Subgrade Pressure (psi)

Inside Middle Outside

DFST Pressure Cells (Under Crib) - 8/1/2003 CW 40 mph, Short Consist

-2

0

2

4

6

8

10

12

14

14 15 16 17 18 19 20 21

Time (sec.)

Subgrade Pressure (psi)

Inside Middle Outside

DFST Pressure Cells (Under Tie) - 8/1/2003 CW 40 mph, Short Consist

-2

0

2

4

6

8

10

12

14

14 15 16 17 18 19 20 21

Time (sec.)

Subgrade Pressure (psi)

Inside Middle Outside

IDBT Pressure Cells (Under Crib) - 8/1/2003

 CW 40 mph, Short Consist

-2

0

2

4

6

8

10

12

14

10 11 12 13 14 15 16

Time (sec.)

Subgrade Pressure (psi)

Inside Middle Outside

Figure 67. Subgrade Pressure under Short Test Consist
79

Figure 68 shows the statistical values (minimum, average, maximum, and standard deviation) of 

subgrade pressures recorded under the train operation at FAST in 2003. Pressures were obtained

based on the peak values corresponding to all passing wheels recorded during that test. Again, 

the maximum subgrade pressure was lower than 12 psi. In addition, subgrade pressure did not 

vary much from under the tie to under the crib for both the DFST and the IDBT. Across the 

track, the distribution of subgrade pressure appeared to be affected by the distribution of vertical 

wheel load between the two rails, particularly for the IDBT; for instance, higher vertical wheel 

load on the high (outside) rail caused higher subgrade pressure on the high rail side.

DFST Pressure Cells - Under Tie

0

2

4

6

8

10

12

14

Inside Middle Outside

Subgrade Pressure (psi)

Min Avg Max Std Dev

DFST Pressure Cells - Under Crib

0

2

4

6

8

10

12

14

Inside Middle Outside

Subgrade Pressure (psi)

Min Avg Max Std Dev

IDBT Pressure Cells - Under Tie

0

2

4

6

8

10

12

14

Inside Middle Outside

Subgrade Pressure (psi)

Min Avg Max Std Dev

IDBT Pressure Cells - Under Crib 

0

2

4

6

8

10

12

14

Inside Middle Outside

Subgrade Pressure (psi)

Min Avg Max Std Dev

Figure 68. Subgrade Pressure under FAST Train

7.3 Long-Term Use of Subgrade Pressure Cells

Subgrade pressure measurements were also taken under train operations at FAST in January and 

October 2005. A careful examination of the data recorded by some pressure cells showed 

significant reductions in subgrade pressure compared with the readings in 2003. As there were 

no dramatic changes of the slab track or the load environment, which might have explained the 

large reductions, a decision was made not to use the data recorded from the tests conducted in 

2005 to quantify the slab track performance under HAL train operation.
80

One hypothesis for the reduction of the subgrade pressure readings was the gap development 

under the concrete slab. The soil cement that was used to cover a pressure cell might not have 

been compacted to the same stiffness as the soil cement layer installed earlier. Over time, the 

base of the concrete slab might have bridged over some pressure cells, leading to reduced 

readings of subgrade pressure by those cells. Another hypothesis focused on questions of the 

long-term performance of the pressure cells themselves. In fact, no-load (without trains) 

readings were compared among the three tests from 2003 to 2005, and the comparison indicated 

significant changes of no-load readings for most of the cells. This indicated a possible long-term 

performance issue with those cells.
81

8. Vibration Attenuation of Slab Track

As part of the testing program, vibration measurements were taken to quantify the vibration 

environment of the slab track test section as well as how much attenuation was achieved from the 

vibration generated on the rails to the vibration generated on the concrete slab. 

Because of the rigid behavior of the concrete slab, slab track designs must provide adequate 

resilience and damping to attenuate vibration generated at the wheel-rail interface, even though 

the slab track generates lower dynamic vehicle-track interaction forces than conventional 

ballasted track (see Section 5).

8.1 Instrumentation for Vibration Measurement

Accelerometers were used to measure vertical vibrations of the rails and the concrete slab. 

Figure 69 shows the general arrangements of accelerometers installed on each slab track test 

section. As shown, six accelerometers were used: four at the center of each slab (two for the 

rails and two for the slab), and two in the transition for the rails. Again, the sampling rate was 

2,048 Hz with a 256-hertz low-pass filter.

Figure 69. Arrangement of Accelerometers for Vibration Measurement

Figure 70 shows the accelerometers installed on the rail and the slab. On the slab track (IDBT or 

DFST), the accelerometers (shown next to the arrow pointers) were installed on the rail base and

the slab surface near the LVDT transducers used for rail-to-slab deflection measurement (refer to 

Section 6). Accelerometers were installed on the rail base for rail vibration measurement in the 

transitions.

Vibration measurements were taken in July and August 2003 following the construction of the 

slab track.
82

Figure 70. Accelerometers Installed in Slab Track (arrows) and in Transition

8.2 Test Results

8.2.1 Analysis in Time Domain

In Figure 71, the light gray lines show the accelerations recorded on the rails while the black 

lines show the accelerations recorded on the slab surface. As illustrated, for either slab (DFST or 

IDBT), vibration was attenuated greatly from the rails to the concrete slab. Compared with the 

magnitudes of vibration measured from the rails, vibration measured on the slab surface can be 

considered insignificant. Attenuation was achieved by installing rubber pads between the rails 

and the concrete slab in the DFST and installing rubber boots/pads between the block ties and the 

concrete slab in the IDBT. Figure 71 shows the vibration attenuation test results obtained under 

the short test consist traveling 40 mph in the CCW direction.

The vibration recorded on the rails was higher for the DFST than for the IDBT. Regardless of 

the slab track type, no obvious difference can be seen between the vibrations measured on the 

high and low rails. 

Figure 72 shows acceleration test results obtained on the rails in both transition areas. Again, no 

obvious trend can be seen as far as the difference between the high and low rails. As compared 

with the rail vibrations measured in the slab areas, transitions did not measure higher vibration in 

terms of vertical acceleration.

Figure 73 and Figure 74 show the vibration test results obtained when the short consist was 

traveling at 40 mph in the CW direction. The test results were essentially similar to those 

obtained when the short test consist was traveling at 40 mph in the CCW direction (Figure 71

and Figure 72). For example, the test results again showed great attenuation of vibration from 

the rail to the slab by resilient rubber pads (DFST) or rubber boots and pads (IDBT). 
83

Figures 71–74 illustrate that acceleration data was rather noisy, compared with that shown in 

previous sections. In addition, no obvious peaks could be identified that corresponded to 

individual passing wheels, unlike the data recorded using other wayside transducers.

Figure 71. Vibration Attenuation from Rail-to-Slab (Short Consist in CCW Direction)

Figure 72. Rail Vibration in Transitions (Short Consist in CCW Direction)

DFST High Rail Accelerometers - 8/1/2003 CCW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

6 7 8 9 10 11 12 13 14 15 16

Time (sec.)

Acceleration (g)

Rail Slab

DFST Low Rail Accelerometers - 8/1/2003 CCW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

6 7 8 9 10 11 12 13 14 15 16

Time (sec.)

Acceleration (g)

Rail Slab

IDBT Low Rail Accelerations - 8/1/2003 CCW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

10 11 12 13 14 15 16 17 18 19 20

Time (sec.)

Acceleration (g)

Rail Slab

IDBT High Rail Accelerometers - 8/1/2003 CCW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

10 11 12 13 14 15 16 17 18 19 20

Time (sec.)

Acceleration (g)

Rail Slab

DFST Transition Accelerometers - 8/1/2003

CCW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

3 4 5 6 7 8 9 10 11 12 13

Time (sec.)

Acceleration (g)

Low Rail High Rail

IDBT Transition Accelerometers - 8/1/2003

CCW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

13 14 15 16 17 18 19 20 21 22 23

Time (sec.)

Acceleration (g)

Low Rail High Rail
84

DFST High Rail Accelerometers - 8/1/2003 CW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

12 13 14 15 16 17 18 19 20 21 22

Time (sec.)

Acceleration (g)

Rail Slab

DFST Low Rail Accelerometers - 8/1/2003 CW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

12 13 14 15 16 17 18 19 20 21 22

Time (sec.)

Acceleration (g)

Rail Slab

IDBT High Rail Accelerometers - 8/1/2003 CW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

8 9 10 11 12 13 14 15 16 17 18

Time (sec.)

Acceleration (g)

Rail Slab

IDBT Low Rail Accelerometers - 8/1/2003

CW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

8 9 10 11 12 13 14 15 16 17 18

Time (sec.)

Acceleration (g)

Rail Slab

Figure 73. Vibration Attenuation from Rail-to-Slab (Short Consist in CW Direction)

DFST Transition Accelerometers - 8/1/2003

CW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

15 16 17 18 19 20 21 22 23 24 25

Time (sec.)

Acceleration (g)

Low Rail High Rail

IDBT Transition Accelerometers - 8/1/2003 CW 40 mph, Short Consist

-25

-20

-15

-10

-5

0

5

10

15

20

25

6 7 8 9 10 11 12 13 14 15 16

Time (sec.)

Acceleration (g)

Low Rail High Rail

Figure 74. Rail Vibration in Transitions (Short Consist in CW Direction)
85

Figure 71 through Figure 74 show the acceleration results obtained under the short test consist. 

Vibration measurements were also taken under the train at FAST. As a result of hundreds of 

axles under each train, the data recorded were processed to obtain the statistical values. Unlike 

the statistical values calculated for other wayside data recorded under the train, acceleration 

responses were processed to obtain values for the following: 95th percentile, 98th percentile and 

maximum for all positive acceleration data, minimum, 2nd percentile, and 5th percentile for all 

negative acceleration data (Figure 75). Also unlike the statistical values obtained for other 

wayside data in which the basis of the statistical values were all peak values corresponding to 

individual passing wheels, the statistical values for accelerations were calculated based on the 

entire time histories recorded as it was not possible to identify peak acceleration response values 

corresponding to individual passing wheels.

Rail Accelerometers - 8/1/2003

CCW 40 mph, FAST Train 

-25.0

-20.0

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

20.0

25.0

IDBT Rail - Low Rail IDBT Rail - High Rail DFST Rail - Low Rail DFST Rail - High Rail

Acceleration (g)

95% 98% Max 5% 2% Min.

Slab Accelerometers - 8/1/2003

CCW 40 mph, FAST Train

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

IDBT Slab - Low Rail IDBT Slab - High Rail DFST Slab - Low Rail DFST Slab - High Rail

Acceleration (g)

95% 98% Max 5% 2% Min.

Figure 75. Vibration Attenuation from Rail to Slab
86

As a result of the use of the entire time history data as the basis for the statistical values shown in 

Figure 75, a big difference exists between a maximum and a 98th or 95th percentile (e.g., the 

98th percentile is a magnitude larger than 98 percent of the data used in the analysis) or between 

a minimum and a 2nd or 5th percentile.

Nevertheless from the comparisons shown in Figure 75, vibrations, measured on the rails, were 

reduced greatly when they were measured on the slab track regardless of track type or whether 

they were obtained from the high or low rail. The maximum or minimum accelerations ranged 

between 11 and 23g (absolute values) when measured on the rails as compared with between 

only 0.4 and 1.7g when measured on the slab. On average, it can be estimated that from the rail 

to the slab attenuation was achieved by a factor of 20.

Figure 76 shows the statistical values of vibration recorded in the transition to the IDBT. As

mentioned earlier, magnitude vibrations measured on the rails in the transitions were similar to 

those measured in the slab.

Transition Accelerometers - 8/1/2003

CCW 40 mph, FAST Train

-20.0

-15.0

-10.0

-5.0

0.0

5.0

10.0

15.0

20.0

IDBT - Low Rail IDBT - High Rail

Acceleration (g)

95% 98% Max 5% 2% Min.

Figure 76. Rail Vibration in Transitions

8.2.2 Analysis in Frequency Domain

Analysis of vibration attenuation was also performed in frequency domain. Figure 77 shows 

vibration attenuation from the rail to the slab in terms of vibration energy (power spectrum 

density (PSD)) at various frequencies. As shown, vibration energy was reduced across the entire 

spectrum from the rail to the slab. In addition, the large vibration energy measured on the rail at 

higher frequencies (above 100 Hz) was greatly attenuated when it was transmitted to the slab.
87

Figure 77. Vibration Attenuation in Frequency Domain from Rail to Slab

IDBT High Rail

0 50 100 150 200 250 300 350 400

PSD

0

1x106

2x106

3x106

4x106

IDBT Slab Under High Rail

Frequency (Hz)

0 50 100 150 200 250 300 350 400

PSD

0

10x103

20x103

30x103

40x103

PSD

DFST High Rail

0 50 100 150 200 250 300 350 400

PSD

0

2x106

4x106

6x106

8x106

10x106

DFST Slab Under High Rail

Frequency (Hz)

0 50 100 150 200 250 300 350 400

PSD

0

10x103

20x103

30x103

40x103

50x103

60x103
88

9. Other Measurements of Slab Track

Some of the slab track measurements were taken to provide the actual test data to verify the slab 

track analysis and design procedures developed for shared heavy-freight and high-speed train 

service (refer to Introduction). As part of the slab track testing program, the following test data 

were obtained and provided to PCA/CTL for that purpose:

 Rail bending strain at rail base 

 Strain of concrete slab surface

 Strain of steel reinforcement bars used in concrete slab

Unlike the test results presented and discussed in previous sections, those presented here were 

not used directly for quantifying the slab track performance under HAL train operation. 

Therefore, a brief summary of the data is given but the data are not compared with the test data 

obtained using the other wayside transducers. 

9.1 Instrumentation for Strain Measurement

Strain gages for measuring rail bending were installed at the top of rail bases (see Figure 38). For 

each slab track (IDBT or DFST), both high and low rails were instrumented for bending strain 

measurement at the rail base. The rail bending strain gages were installed between two ties and 

fastener supports but were close to them.

On the concrete slab surface of the IDBT or the DFST, three strain gages were installed in the 

longitudinal direction: one on the outside, one in the middle, and one on the inside. In addition, 

one strain gage was installed in the lateral direction in the middle of the slab track. Figure 78

illustrates the locations and orientations of the four strain gages installed on the concrete slab 

surface. Figure 79 shows a pair of strain gages installed on the concrete slab surface at the 

middle location.

Strain gages were used on the top and bottom steel bars (see Figure 9 and Figure 11) instead of 

the steel reinforcement bars used in the concrete slab (Phase 1 slab in the case of the IDBT). As 

shown in Figure 78, four strain gages were used on the top steel bars: three in the longitudinal 

direction and one in the lateral direction. For the bottom steel bars, six strain gages were 

installed: three in the longitudinal direction and three in the lateral direction. Note, the backup 

strain gages shown in Figure 78 were installed in case some did not work. Figure 79 shows 

strain gages installed on steel bars before the concrete was poured to form the slab.

Strain measurements under the HAL train operation at FAST were taken in July and 

August 2003. Again, the sampling rate for collecting data was 2,048 Hz with a 256-hertz lowpass filter. The data were recorded with data collected using the other wayside transducers, as 

discussed in previous sections. 
89

Figure 78. Arrangement of Strain Gages on Slab Surface and Reinforcement Bars

Figure 79. Strain Gages Installed on Slab Surface and Steel Bar
90

9.2 Test Results

Test results obtained under the short HAL test train are presented in three sections: one for rail 

bending strains, one for concrete surface strains, and one for steel reinforcement bar strains. A

positive value indicates tensile strain and a negative value indicates compressive strain. 

Unlike the data signals obtained using the other wayside transducers, the initial offsets of strain 

signals (if present) were not adjusted to zero for the purpose of showing dynamic responses 

due to dynamic wheel loads. This is because a negative initial reading for the concrete slabs 

might indicate a certain amount of compressive stress already applied to the concrete, which 

would help to prevent crack development resulting from the possible tensile stress caused by 

dynamic wheel loads. 

9.2.1 Rail Base Bending Strain

Figure 80 shows the rail bending strain test results obtained under the short test consist when it 

was traveling at 40 mph in the CCW direction. The magnitudes of rail bending strain measured 

on the high and low rails for both the DFST and the IDBT are low as compared with the 

allowable rail bending strain (i.e., allowable bending stress) for the rail steel. As expected, rail 

bases are primarily in tension under dynamic wheel loadings.
91

DFST Rail Bending Strain - 8/1/2003

 CCW 40 mph, Short Consist

-75

-25

25

75

125

175

225

8 9 10 11 12 13 14

Time (sec.) Strain (me)

High Rail Low Rail

IDBT Rail Bending Strain - 8/1/2003

CCW 40 mph, Short Consist

-75

-25

25

75

125

175

225

12 13 14 15 16 17 18

Time (sec.) Strain (me)

High Rail Low Rail

Figure 80. Rail Bending Strain under Short Test Consist in CCW Direction

Figure 81 shows the rail bending strain test results obtained when the short consist was traveling

in the CW direction at 40 mph. The results are similar to those shown in Figure 80 for the test 

run in the CCW direction.
92

IDBT Rail Bendinig Strain - 8/1/2003

CW 40 mph, Short Consist

-75

-25

25

75

125

175

225

10 11 12 13 14 15 16

Time (sec.) Strain (me)

High Rail Low Rail

DFST Rail Bending Strain - 8/1/2003

CW 40 mph, Short Consist

-75

-25

25

75

125

175

225

14 15 16 17 18 19 20 21

Time (sec.) Strain (me)

High Rail Low Rail

Figure 81. Rail Bending Strain under Short Test Consist in CW Direction (2003)

9.2.2 Concrete Surface Strain

Figure 82 shows the strain measurement results for the eight strain gages installed on the slab 

surface (four each for the DFST and IDBT). The top two graphs show the longitudinal strains 

measured on the outside, at the middle, and on the inside for the DFST and IDBT, respectively. 

The bottom graph shows the lateral strain test results obtained at the middle of the slab track for 

both the DFST and the IDBT. 
93

DFST Longitudinal Slab Strain - 8/1/2003

CCW 40 mph, Short Consist

-120

-90

-60

-30

0

30

8 9 10 11 12 13 14

Time (sec.) Strain (me)

Inside Middle Outside

IDBT Longitudinal Slab Strain - 8/1/2003

CCW 40 mph, Short Consist

-40

-30

-20

-10

0

10

12 13 14 15 16 17 18

Time (sec.) Strain (me)

Inside Middle Outside

Lateral Slab Strain - 8/1/2003

CCW 40 mph, Short Consist

-20

-15

-10

-5

0

5

12 13 14 15 16 17 18

Time (Sec.) Strain (me)

IDBT DFST

Figure 82. Slab Surface Strains under Short Test Consist in CW Direction
94

Figure 82 shows that the longitudinal compressive strains were generally larger than the lateral 

compressive strains, particularly for the DFST slab. On the surface of the DFST slab, no tensile 

strain in either the longitudinal or the lateral direction was generated under dynamic wheel loads,

whereas, the surface of the IDBT slab experienced a small amount of tensile strain in either 

orientation. 

As described in Section 2, the DFST slab was reinforced; the entire slab acts as a main structural

layer. For the IDBT, the Phase 1 (base) slab was reinforced; this is the main structural layer 

supporting dynamic wheel loads. The Phase (top) 2 slab was not reinforced; it is used mainly to 

hold independent dual block ties. However, the Phase 2 slab is designed for composite action 

with the roughened Phase 1 slab. The comparison of longitudinal strain test results on the 

surfaces of the DFST and IDBT slabs appeared to reflect the structural difference between these 

two slabs. This may be explained by the construction sequence.

9.2.3 Steel Bar Strain

Figure 83 shows the strain measurement results from the eight strain gages installed on the top 

steel bars (four each for the DFST and the IDBT). The top two graphs show the longitudinal 

strains measured on the outside (under the high rail), at the middle, and on the inside (under the 

low rail) for the DFST and IDBT, respectively. The bottom graph shows the lateral strain test 

results obtained at the middle of the slab track for both the DFST and the IDBT.

Again, longitudinal compressive strains were much larger than lateral compressive strains, 

particularly for the DFST slab. The DFST slab showed larger compressive strains than the IDBT 

slab because the top steel bars of the IDBT slab are in Phase 1 concrete and are closer to the 

neutral axis of the composite section than the top steel bars in the DFST slab. Similarly, in the 

lateral direction, the measured strain from a top steel bar in the DFST was larger than that 

measured from a top bar in the IDBT Phase 1 slab.

Top steel bars for either slab were primarily in the compression mode in the longitudinal 

direction under dynamic wheel loads. For either slab track, the longitudinal direction is the 

major direction as far as the stress state is concerned. The compressive strain or stress in the 

longitudinal direction is expected to be higher than in the lateral direction. Also, concrete 

shrinks during curing, which causes slight compression in the top and bottom longitudinal 

reinforcement. 
95

DFST Longitudinal Top Rebar Strain - 8/1/2003

CCW 40 mph, Short Consist

-160

-130

-100

-70

-40

-10

20

50

80

8 9 10 11 12 13 14

Time (sec.) Strain (me)

Inside Middle Outside

IDBT Longitudinal Top Rebar Strain - 8/1/2003

CCW 40 mph, Short Consist

-80

-60

-40

-20

0

20

40

12 13 14 15 16 17 18

Time (sec.) Strain (me)

Inside Middle Outside

Lateral Top Rebar Strain - 8/1/2003

CCW 40 mph, Short Consist

-15

-10

-5

0

5

10

12 13 14 15 16 17 18

Time (sec.) Strain (me)

IDBT DFST

Figure 83. Strains of Top Steel Bars under Short Test Consist in CCW Direction
96

Figure 84 shows longitudinal strain measurement results for the steel reinforcement bars at the 

bottom of the concrete slabs. As shown in Figure 78, each slab had six strain gages installed on 

the bottom steel bars: three on the longitudinal bars and three on the steel bars. In Figure 84, the 

top graph shows the longitudinal strains measured in the DFST and the bottom graph shows the 

test results obtained in the IDBT.

As expected, the steel reinforcement bars were primarily in the tension mode regardless of the 

slab type (DFST or IDBT). Between the two slabs, the magnitudes of tensile strains were 

basically of the same order.

DFST Bottom Longitudinal Rebar Strain - 8/1/2003

CCW 40 mph, Short Consist

-60

-40

-20

0

20

40

60

80

100

120

8 9 10 11 12 13 14

Time (sec.) Strain (me)

Inside Middle Outside

IDBT Bottom Longitudinal Rebar Strain - 8/1/2003

CCW 40 mph, Short Consist

-60

-40

-20

0

20

40

60

80

100

120

12 13 14 15 16 17 18

Time (sec.) Strain (me)

Inside Middle Outside

Figure 84. Longitudinal Strains of Bottom Steel Bars
97

Figure 85 shows lateral strain measurement results for the steel reinforcement bars at the bottom 

of the concrete slabs. The top graph shows the lateral strains measured in the DFST and the 

bottom graph shows the lateral strains measured in the IDBT.

As seen with the longitudinal strains measured, steel reinforcement bars installed in the lateral 

direction were primarily in the tension mode under dynamic wheel loads. Lateral steel bars 

experienced much lower strain responses than the longitudinal steel bars. As mentioned earlier, 

the major stress in the concrete slab was in the longitudinal direction. 

DFST Bottom Lateral Rebar Strain - 8/1/2003

CCW 40 mph, Short Consist

-10

-5

0

5

10

15

20

25

30

8 9 10 11 12 13 14

Time (sec.) Strain (me)

Inside Middle Outside

IDBT Bottom Lateral Rebar Strain - 8/1/2003

CCW 40 mph, Short Consist

-10

-5

0

5

10

15

20

25

30

12 13 14 15 16 17 18

Time (sec.) Strain (me)

Inside Middle Outside

Figure 85. Lateral Strains of Bottom Steel Bars
98

10. Summary and Conclusions

The Slab Track Field Testing and Demonstration Program for Shared Freight and High-Speed 

Passenger Service project was completed to demonstrate the durability of the slab track for 

39-ton axle loads while maintaining the track geometry conditions for a Class 9 track. More 

specifically, the program was carried out to characterize slab track stiffness conditions, to 

quantify slab track dynamic responses and performance under HAL train operation, and to 

provide test data for validating slab track analysis and design methodologies for shared heavyfreight and high-speed train service.

In July 2003, two types of slab track (DFST and IDBT) were installed on the HTL at TTC. The 

slab track test section was in a 5-degree curve with 4-inch superelevation. It was 500 ft long and

consisted of 250 ft of IDBT and 250 ft of DFST. The transition from each slab to the ballasted 

track was in a spiral from a 5-degree curve to tangent track. 

The testing program concluded in the summer of 2006. Over a period of 3 yr, a total of 170 MGT

of HAL traffic was accumulated on the slab track test section, exceeding the target tonnage of 

150 MGT. During the period of testing and monitoring, various measurements were conducted 

to quantify the slab track responses and performance under HAL train operation. 

10.1 Track Geometry Performance of Slab Track

The slab track test section in the HTL demonstrated its capability of supporting HAL train 

operation while maintaining the track geometry conditions for a Class 9 track. During the 3 yr of 

testing and the 170 MGT of accumulated traffic, little track geometry degradation was measured

and no track geometry maintenance was required for surface, alignment, gage, or crosslevel of 

the slab track test section. From the beginning of the testing program until its completion, there 

was little cumulative settlement and little lateral movement of the slab track. 

An alignment adjustment was done near the end of the DFST slab track following the 

construction of the slab track test section. The misalignment was due to the severe transition 

conditions from a Class 9 slab track to a Class 4 ballasted track and a change of curvature from 

the 5-degree curve to a spiral.

The surface condition of the slab track was superior to that of the adjacent ballasted track. 

Several spot tamping operations were performed in the transition areas to smooth out differential 

track settlement accumulated in the ballasted transitions. 

10.2 Slab Track Stiffness Characteristics 

Both the IDBT and the DFST were built with uniform vertical track stiffness. When measured 

following the construction of the slab track test section, the IDBT showed an average track 

modulus of 3,000 lb/in/in and the DFST showed an average track modulus of 2,100 lb/in/in. 

These values, especially for the DFST, were lower than originally expected and were due to the 

use of extremely resilient rubber boots and pads.
99

The installation of 25-foot transitions became unnecessary at least in terms of track stiffness, as

the slab track test section (DFST or IDBT) was either more resilient than or resilient as the 

adjacent ballasted track. 

During the 3-year period of testing, the increase in track modulus for the DFST was moderate

but the increase for the IDBT was significant. This increase was caused by the gradual deposit of 

fine windblown sand into spaces between the IDBT components as discovered in November 

2006 during the IDBT inspection. This process caused an increase in track modulus by limiting 

the deflection of the block ties within the rubber boots. Some of the deposited sand was flushed 

out when combined with rainwater under passing trains. The flushing process had caused the 

buildup of fine gray material around the block ties. One of the IDBT pads was tested in a 

laboratory following the inspection, and it was determined that the stiffness of the pad was 

within the tolerance limits set by the manufacturer of the IDBT block-tie system. 

In terms of lateral gage strength, both the IDBT and the DFST tracks showed more uniform 

lateral gage strength or stiffness than the adjacent ballasted track. For the DFST, there had been 

a significant decrease in gage strength in terms of delta gage measured by the TLV. From 2 to 

169 MGT, delta gage measured under the TLV test loads (33-kilopound vertical wheel load and 

18-kilopound lateral wheel load) increased from 0.3 to 0.5 in on the average. Extremely resilient 

pads, such as those used in the DFST, may be of concern for HAL operation. With the IDBT, 

there was little gage strength degradation in terms of delta gage, although unloaded track gage 

increased from 56.8 to 57.1 in on the average, with the maximum being 57.2 in. Compared with 

the DFST, resilience of rubber boots and pads used in the IDBT had less of an influence on gage 

strength or stiffness because the boots and pads were installed at the tie-slab interface. 

10.3 Dynamic Wheel/Rail Forces on Slab Track 

Because of superior track geometry and resilient pads and boots, the slab track test section 

generated lower dynamic vertical and lateral wheel loads than the ballasted track of the same 

curvature and superelevation. The maximum vertical load generated in the slab track was 58 kip

as compared with 73 kip generated on a ballasted track. The maximum lateral wheel load 

generated in the slab track was 20 kip as compared with 24 kip in the ballasted track. Note that 

the slab track test section located in a 5-degree curve with 4-inch superelevation was 

underbalanced at the nominal train operating speed of 40 mph on the HTL, meaning that higher 

vertical wheel load was applied on the high rail than on the low rail.

Over the 3 yr of testing, no significant increases were observed in either the vertical or lateral 

dynamic wheel loads, particularly those generated on the high rail. However, lateral wheel loads 

generated at the ends of the slab track (transition areas) increased. IWS test results showed a 

significant increase of lateral wheel load at the ends of the slab test section, particularly when the 

test train was exiting the slab track. With regard to vertical wheel load, the dynamic responses 

were also higher (up to 25 percent) in the transitional areas but did not increase during the three 

tests conducted from 2003 through 2005.
100

10.4 Slab Track Deflection

Slab track deflection occurred primarily between the rail and the concrete slabs due to resilient 

pads (DFST) or rubber boots and pads (IDBT). Only a small amount of deformation was 

recorded from the underlying subbase and subgrade layers. 

Vertical and lateral rail-to-slab deflection test results were consistent with dynamic wheel loads 

and track stiffness test results measured at the same time. Higher dynamic wheel loads and 

lower track stiffness would correspond to larger rail-to-slab deflections regardless of the slab 

track type. For the DFST, the maximum vertical rail-to-slab deflection was 0.25 in and the 

maximum lateral rail-to-slab deflection was 0.1 in, both recorded on the high rail. For the IDBT, 

the maximum vertical rail-to-slab deflection was 0.15 in and the maximum lateral rail-to-slab

deflection was 0.07 in, which was again measured on the high rail.

From 2003 to 2006, little increase measured in vertical rail-to-slab track deflection occurred for 

the DFTS. There was an increasing trend of lateral rail-to-slab deflection, which appeared 

consistent with the trend of decreasing gage strength for the DFST. The general trends for 

vertical and lateral rail-to-slab deflections were decreasing, particularly for the deflections on the 

high rail for the IDBT. These trends appeared to be consistent with the track stiffness increase 

for the IDBT slab track.

10.5 Subgrade Pressure and Deformation under Slab Track 

The maximum subgrade pressure generated under HAL vehicles was 12 psi, well below the 

compressive strength of the subgrade soil. The relatively low subgrade pressure with respect to 

soil strength explains the small amount of subgrade deformation generated under HAL train 

operation. Under the slab track test section, the maximum deformation recorded in the subbase 

or subgrade was less than 0.06 in.

10.6 Vibration Attenuation 

In the slab track test section, vibration attenuation was achieved through use of rubber pads 

(DFST) or rubber boots and pads (IDBT). The vibration measurements showed a large amount 

of vibration attenuation from the rail to the slab regardless of slab track type. Under HAL train 

operations at 40 mph, the maximum acceleration recorded on the rails ranged between 10 and 

25g (absolute value) whereas that on the slab ranged between only 0.4 and 2g (absolute value). 

On average, attenuation was achieved by a factor of 20. 

With regard to vibration measured on the rails, no obvious trends could be identified between the 

transitions and the slab track or between the high and low rails. Analysis of vibration attenuation 

in frequency domain showed the attenuation of vibration energy across the entire spectrum. In 

addition, the large amount of vibrations above 100 Hz was greatly attenuated from that measured 

on the rails to that measured on the concrete slab.

10.7 Other Performance Parameters

For a total of 170 MGT of HAL traffic, no rail defects were recorded in the slab track test 

section, nor were any weld defects or failures reported for the 14 thermite welds used in the test 
101

section. For comparison purposes, the average weld life in similar 5-degree curves in the HTL 

was approximately 80 MGT. In addition, no significant wear of either high or low rails in the 

test section was observed; nor was rail corrugation development noted. According to the 

locomotive engineers who operate the trains at FAST, the slab track test section provided the 

best ride quality of the entire HTL.

10.8 Additional Notes

The results, discussions, and conclusions presented in this report were based on testing of the 

slab track for a 3-year period (July 2003–July 2006) under a total accumulated traffic of 

170 MGT. In September 2006, PCA and FRA gave approval for extending the slab track test for 

another 2 yr, until September 2008.

In addition to the tests presented and discussed in this report, other tests were done on the slab 

track test section. PCA and CTL personnel mapped the cracking of the concrete slabs twice 

throughout the duration of the slab track testing, which showed normal cracking distribution and 

growth for the concrete slab. Ground-penetrating radar testing done for the slab track in 

September 2003 showed no voids or loss of support between the base of the slab and the soil 

cement layer (Smith, 2005).

10.9 Recommendations

As the slab track test section continues to be subjected to HAL train operations at FAST, it is 

recommended that performance monitoring continue in terms of track geometry conditions. Gage 

strength testing is also recommended to determine if gage strength of the DFST may further 

degrade under HAL. For either slab (IDBT or DFST), testing of rubber boots or pads for issues 

such as possible temperature increase under train operation and change of resilient property over 

time may provide further insight regarding their eventual life cycle under HAL train operation. 

Finally, it is recommended that a test section of slab track be installed in revenue service with 

shared heavy-freight and high-speed train operations.
102

11. References

Ball, C.G. (2004). Slab Track Laboratory Test Program. PCA R&D, Serial No. 2795. Portland 

Cement Association, Skokie, IL.

Bilow, D.N., & Li, D. (2005). Concrete Slab Track Test on the High Tonnage Loop at the 

Transportation Technology Center. In Proceedings of the AREMA Annual Conference, Chicago, 

IL.

Kucera, W.P., Bilow, D.N., Ball, C.G., & Li, D. (2003). Laboratory Test Results and Field Test 

Status of Heavy Axle Loads on Concrete Slab Track Designed for Shared High-Speed Passenger 

and Freight Rail Corridors. In Proceeding of the AREMA Annual Conference, October 5–8, 

Chicago, IL.

Li, D., Thompson, R., Marquez, P., & Kalay, S. (2004). Development and Implementation of a 

Continuous Vertical Track-Support Testing Technique. Transportation Research Record: 

Journal of the Transportation Research Board, U.S. National Academies, no. 1863, pp. 68–73.

Li, D., & Yoshino, D. (2003). Review and Evaluation of Track Designs for Joint High-Speed 

Rail and Heavy Freight Operations. Final Report to Office of Research and Development, FRA. 

TTCI, Pueblo, CO.

Lotfi, H.R., & Oesterle, R.G. (2005). Slab Track for 39-Ton Axle Loads, Structural Design.

PCA R&D, Serial No. 2832. Portland Cement Association, Skokie, IL.

Selig, E.T., & Li, D. (1994). Track Modulus: Its Meaning and Factors Influencing It.

Transportation Research Record: Journal of The Transportation Research Board, U.S. National 

Academies, No. 1470, pp. 47–54.

Selig, E.T., & Waters, J.M. (1994). Track Geotechnology and Substructure Management. 

Thomas Telford.

Smith, S. (2005). As-Built Survey of Slab Track Using Ground Penetrating Radar at 

Transportation Technology Center, Pueblo, Colorado. FRA Contract No. DTR-52-02-P-00263, 

Geo-Recovery Systems, Inc., Golden, CO.

Tayabji, S.D., & Bilow, D.N. (2001). Concrete Slab Track State of the Practice. Transportation 

Research Record: Journal of the Transportation Research Board, U.S. National Academies, 

No. 1742, pp. 87–96.
103

Appendix A.

Report of IDBT Inspection on November 20, 2006

Attendees:

David Bilow, Portland Cement Association

Dingqing Li and two to three trackmen, Transportation Technology Center, Inc.

Purpose:

Measurements of the track modulus at 169 MGT indicated that the stiffness of the IDBT test 

section increased from 3,000 psi to a maximum slightly above 10,000 psi and that the average 

dynamic rail deflection decreased from 0.13 to 0.07 in during the 3 yr of operation. In addition, 

when settlement was measured, the IDBT actually rose 0.1–0.3 in during the operation period. It 

is believed that the increase in track modulus and negative settlement were the results of 

windblown sand infiltrating the space between the block-tie components. The inspection was 

conducted to verify this hypothesis and to determine the condition of the elastomeric pad, boots, 

concrete block tie, and concrete surrounding the block cavity.

Inspection:

1. The temperature at 8 a.m. was 44 °F, and it was sunny with a few clouds. The 

temperature increased to about 60 °F in the afternoon.

2. Dingqing Li selected low rail tie numbers 190, 191, 192, and 193 for removal and 

inspection. The track at this location had the highest track modulus, but not much gray 

material was seen surrounding the blocks ties. 

3. The track crew, which consisted of two men and sometimes a third, unclipped the rail’s 

20 ties each way from the ties to be inspected. The ties to be inspected were not 

unclipped. 

4. Two 15-ton rail jacks were placed on each side of tie numbers 187 and 196. Using the 

jacks the rail was raised 2 in. Five more ties were unclipped in each direction, and one 

jack was moved to just west of tie number 191. The rail was than raised a total of 8 in. 

The boots remained attached to the blocks that were raised. 

5. Block numbers 190 and 191 were unclipped and moved from under the rail. 

6. During the inspection of the cavity, sand was found on the sides and bottom. Some of 

the boot, pad, cavity, and block surfaces were wet because the water from earlier rains 

had not evaporated. 

7. The boots were removed from block ties numbers 190 and 191, and more sand was 

found on the wall of the boots and on the bottom. Also, some sand adhered to the 

bottom of the concrete block. The sand was removed from the cavity and the block and 

placed in the boot to be measured later. 

8. The concrete in the cavity and the block tie were in good condition. There was no 

evidence of cracking or spalling. However, the sides of the block ties contained an 

impression of the ribs of the boots. The impression had a depth of 0.085 in as measured 

by TTCI. The boots and pads were in good condition and did not show any signs of 
104

wear and tear. The boots and pads from numbers 190 and 191, together with the sand,

will be shipped to Clair Ball at CTLGroup.

9. Dingqing Li selected high-rail tie numbers 151 and 152 for removal and inspection. The 

track at this location also had a high track modulus and, compared with tie numbers 190 

and 191, these blocks had much more gray material surrounding them. 

10. The track crew unclipped the rails 25 ties each way from the ties to be inspected. The 

ties to be inspected were not unclipped. 

11. Fifteen-ton rail jacks were placed on each side of tie numbers 151 and 152. Using the 

jacks, the rail was raised a total of 8 in. The boots remained attached to the blocks that

were raised. 

12. Blocks 151 and 152 were unclipped and moved from under the rail. 

13. During the inspection of the cavities, sand 1/8-in thick was found on the sides and

bottom.

14. The boots were removed from the block ties, and more sand was found on the wall of the 

boots and on the bottom. Also, 1/8 to 1/4 inch of sand adhered to the bottom of both 

concrete blocks. The amount of sand observed at tie numbers 151 and 152 was more 

than the amount seen at tie numbers 191 and 192. The surfaces of the pads were wet 

because water from earlier rain had not evaporated.

15. The boot for tie number 151 had a 3-inch-long hole at the corner between the bottom and 

the long sidewall of the boot. This boot will be sent to CTLGroup.

16. The concrete in the cavity and the block-tie concrete were in good condition. There was 

no evidence of cracking or spalling. The sides of block numbers 151 and 152, however,

contained an impression of the ribs of the boots similar to that found in block tie 

numbers 190 and 191. 

17. The boots and pads from tie numbers 190 and 191 and the boot from number 151 were 

replaced with new boots and pads from the spare blocks.

18. Each of the four block ties was placed back into the cavity from which it was removed,

and the rails were lowered onto the ties. All four replaced blocks did not seat and 

remained above their correct position by 3 in. A speed crane was used to try and reseat 

block numbers 190 and 191, which helped somewhat, but the blocks still remained above 

their correct position.

19. Following the inspection, the track crew used a locomotive to push down the blocks that 

were raised during the inspection. A tamper was then used to align the rails into proper 

positions. 

Discussion

The sand under the block, both inside and outside the boot, was the cause of the measured rise in 

the IDBT of 0.1 to 0.3 in. The increase in track modulus was likely caused by the volume of 

sand around the block inside the boot. (The volume of sand will be measured when the material 

is inspected at the CTLGroup.) The sand filled up the spaces within the boot, which interfered

with the block tie’s deflection. Additionally, CTL will test a pad removed during the inspection 

to determine if there was any change in pad stiffness.
105

The gray material found around block tie numbers 151 and 152 was caused by a mixture of 

windblown sand, cement particles, and rainwater being pushed out during train operations. The 

cement particles were the result of localized abrasion of the block ties as evidenced by the 

impression of the boot ribs on the sides of the ties. Rainwater mixed with sand and filled any 

voids that remained between the boot and the block.

Figure A1. IDBT Block Tie Numbers 190 through 193

Figure A2. Tie Number 190, Showing Impressions from the Boot Ribs
106

Figure A3. Cavity of Tie Number 190

Figure A4. Inside of Boot for Tie Number 190
107

Figure A5. Tie Number 190 Pad

Figure A6. Outside of Boot Tie Number 190
108

Figure A7. Cavity of Tie Number 151, Showing Sand in the Bottom

Figure A8. Bottom of Tie Number 151
109

Figure A9. Inside of Boot of Tie Number 151

Figure A10. Pad of Tie Number 151
110

Figure A11. Bottom of Tie Number 152

Figure A12. Tie Number 151, Placed Back into Cavity and Not Fully Seated
111

Figure A13. Tie Number 151, Showing Gray Material Discharged from Tie Cavity

Figure A14. Tie Numbers 191, 192, and 193 Not Fully Seated
112

Appendix B.

Data from January 18, 2007, Test Report
113
114

Abbreviations and Acronyms

AAR Association of American Railroads

CCW counterclockwise

CTL Construction Technology Laboratories

CW clockwise

CWR continuous welded rail

DFST direct fixation slab track

FAST Facility for Accelerated Service Testing

FRA Federal Railroad Administration

HAL heavy axle load

HSR high-speed rail

HTL High Tonnage Loop

IDBT independent dual block track

IWS instrumented wheelsets

LVDT linear variable differential transformer

MCO midchord offset

MDD multidepth deflectometers 

MGT million gross ton

PCA Portland Cement Association

PSD power spectrum density

ROW right-of-way

TGMS track geometry measurement system

TLV track loading vehicle

TOR top-of-rail

TTC Transportation Technology Center

TTCI Transportation Technology Center, Inc.