Comparisons of Railroad Track

and Substructure Computer

Model Predictive Stress Values

and In-Situ Stress Measurements

By: Dr. Jerry G. Rose, Ph.D., PE

Bei Su, MSCE and

Frank Twehues, EIT

Earth Pressure Cell

Measures Predicts Tekscan Sensor

Computer

Geokon Pressure

Cell

Ballast

Subballast/HMA

Wooden Tie

Subgrade

Geokon Pressure

Cell

Tekscan Sensor

Tekscan Sensor

Geokon Pressure Cell

Pressure Cell

Tekscan Sensor

• Geokon Model 3500-2

• 9 in. Diameter

• Strain Gage

• Snap-Master

• Thermistor

Pressure Cell

Cell

Placement

on Asphalt

Pressure Cell

Junction Box

Battery

Pressure Cell Measurement Configuration

View of Tekscan Sensors

Tekscan Measurement

Configuration

•Matrix-based array of

force sensitive cells

•Silver conductive electrodes

•Pressure sensitive ink –

Conductivity varies

•Crossing of ink – strain gauge

Traditional Track Structure

Track Structure With Asphalt Underlayment

– 5-10 feet beyond crossing

– Typical highway dense-graded

base mix

– 0.5% higher asphalt content

Installation of HMA Underlayment by Back-Dumping

Installation of HMA Underlayment Using Paver

HMA

ballast

subballast4 in.

4 in.

12 in.

4 in.

8 in.

8 in.

clay subgrade

10 ft350 ft350 ft

Pueblo, Colorado Longitudinal Section

Existing Conditions at Transportation Technology Center, Pueblo, Colorado

Conway, Kentucky Longitudinal View

Existing Conditions at Conway, Kentucky

clay subgrade

9 in.

8 in.

9 in.

5 in.HMA

ballast

1000 ft 1000 ft

Calibration Test Configuration Using the

Satec Universal Testing Machine.

0

5

10

15

20

25

7 8 9 10 11 12 13 14 15 16 17

Time (s)

HM

A C

om

pre

ssiv

e S

tress (

psi)

Four 6-Axle Locos

Initial 5 Cars

8 in. ballast

5 in. HMA

0

5

10

15

20

4 5 6 7 8 9 10 11 12 13 14 15

Time (s)

HM

A C

om

pre

ssi

ve

Str

ess (

psi

)Four 6-Axle Locos

Initial 5 Cars

8 in. ballast

8 in. HMA

Representative Dynamic

Compressive Stress on

HMA Layer Measured for

Empty Coal Train on CSX

Transportation Mainline

at Conway, KY

0

5

10

15

20

2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5

Time (s)

Co

mpre

ssiv

e S

tre

ss (

ps

i)

subgrade surfaceHMA surface

Dynamic Compressive Pressures Measured on TTCI Test Track

Comparison of the KENTRACK Predictive Values (KPV)

Versus In-Track Data (ITD) for the CSX Mainline at Conway, Kentucky

Thickness

Ballast/HMA

inches

Vertical

Compressive Stress

on Ballast

KPV/ITD, psi

Vertical

Compressive Stress

on HMA

KPV/ITD, psi

Vertical

Compressive Stress

on Subgrade

KPV/ITD, psi

10 / 5 47.9 / 21 / 16 13.6 / -

10 / 8 48.7 / 22 / 15 11.7 / -

Comparison of the KENTRACK Predictive Values (KPV)

Versus In-Track Data (ITD) at TTCI in Pueblo, Colorado

Thickness

Ballast/HMA

inches

Vertical

Compressive Stress

on Ballast

KPV/ITD, psi

Vertical

Compressive Stress

on HMA

KPV/ITD, psi

Vertical

Compressive Stress

on Subgrade

KPV/ITD, kPa

12 / 4 43.5 / - 11.7 / 14.9 8.3 / 8.0

8 / 8 47 / - 21.9 / 14.9 8.2 / 7.7

286,000

lb

62,000

lb

180

lb

13 - 17

psi

2 - 4

psi

6

psi

100 - 200+

psi

Vertical Pressure on Asphalt Surfaces for Various Loadings

In Track Placement During First Test

Scale in PSI

Typical Pressure Distribution

Plot from Tekscan System

Scale in PSI

Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.

Scale in PSI

Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.

Scale in PSI

Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.

Scale in PSI

Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.

Scale in PSI

Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.

Scale in PSI

Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.

Scale in PSI

Figure 5.1: This represents a typical pressure distribution between a steel tie plate and the rail. There is very little contact area. The sensor has a 1200 psi capacity and the red areas indicate saturation zones. The force applied at these areas could and probably are much higher than the 1200 psi recorded and that would lower the overall force recorded.

Scale in PSI

This represents a typical pressure distribution

between a steel tie plate and the rail.

Rail

Mylar Teflon

Tekscan

Sensor

Teflon

Mylar

Rubber Bladder

Tie Plate

Scale in PSI

This represents a typical pressure distribution between a machined

steel tie plate and the rail with an included rubber bladder.

Scale in PSI

This represents a typical pressure distribution between

a polyurethane plastic tie plate and the rail.

0

50

100

150

200

250

300

350

400

450

500

5 Tie

s Bef

ore

Senso

r

4 Tie

s Bef

ore

Senso

r

3 Tie

s Bef

ore

Senso

r

2 Tie

s Bef

ore

Senso

r

1 Tie

Bef

ore

Sen

sor

Dire

ctly A

bove

Sen

sor

1 Tie

s Pas

t Sen

sor

2 Tie

s Pas

t Sen

sor

3 Tie

s Pas

t Sen

sor

4 Tie

s Pas

t Sen

sor

5 Tie

s Pas

t Sen

sor

Lead Wheel Position

Avera

ge P

ressu

re (

psi) Positioning of Lead Wheel

with Respect to Sensor

Snapshot of the Lead Wheel

Directly above the Sensor Lead Wheel Over

Sensor F = 20985 lbf, P = 437 psi

0

100

200

300

400

500

600

700

10 T

ies Bef

ore

Sen

sor

8 Tie

s Bef

ore

Senso

r

6 Tie

Bef

ore

Sen

sor

4 Tie

s Bef

ore

Senso

r

2 Tie

s Bef

ore

Senso

r

Dire

ctly A

bove

Sen

sor

2 Tie

s Pas

t Sen

sor

4 Tie

s Pas

t Sen

sor

6 Tie

s Pas

t Sen

sor

8 Tie

s Pas

t Sen

sor

10 T

ies Pas

t Sen

sor

Lead Wheel Position

Avera

ge P

ressu

re (

psi)

Positioning of Lead Wheel

with Respect to Sensor

Snapshot of the Lead Wheel

Directly above the Sensor

Lead Wheel Over

Sensor F = 25372 lbf, P = 529 psi

Rear Tires of Tractor of a 151,000 lb Loaded Coal Truck on Concrete

Crossing of Kentucky Coal Terminal, Mile Post 6.6. May 25, 2004

9842 lb

72.93 in^2

135 psi

Front Tire of a CSXT Suburban on Asphalt Parking Lot in Ashland Oil

Company. May 25, 2004

1652 lb 75 PSI

22.15 in^2

Rear Tire of a CSXT Suburban on Asphalt Parking Lot in Ashland Oil Company.

May 25, 2004

2197 lb 81 PSI

27.15 in^2

Mylar Teflon

Tekscan

Sensor

Teflon

Mylar

Tire Tread

Asphalt Surface

FINDINGS

• KENTRACK -- utilized to predict stresses in the track structure and foundation

• Earth Pressure Cells -- provide direct measurement of

pressures (stresses) in the track structure and foundation

• Computer Predictions -- compare favorably with Pressure Cell Measurements at the ballast/subballast and subballast/subgrade interfaces

• Pressure Cells -- technique presently being developed for tie/ballast interface pressure measurements

FINDINGS

• KENTRACK -- utilized to predict stresses in the track structure and foundation

• Earth Pressure Cells -- provide direct measurement of pressures (stresses) in the track structure and foundation

• Computer Predictions -- compare favorably with Pressure Cell Measurements at the ballast/subballast and subballast/subgrade interfaces

• Pressure Cells -- technique presently being developed for tie/ballast interface pressure measurements

FINDINGS

• KENTRACK -- utilized to predict stresses in the track structure and foundation

• Earth Pressure Cells -- provide direct measurement of pressures (stresses) in the track structure and foundation

• Computer Predictions -- compare favorably with Pressure Cell Measurements at the ballast/subballast and subballast/subgrade interfaces

• Pressure Cells -- technique presently being developed for tie/ballast interface pressure measurements

FINDINGS

• KENTRACK -- utilized to predict stresses in the track structure and foundation

• Earth Pressure Cells -- provide direct measurement of pressures (stresses) in the track structure and foundation

• Computer Predictions -- compare favorably with Pressure Cell Measurements at the ballast/subballast and subballast/subgrade interfaces

• Pressure Cells -- technique presently being developed for tie/ballast interface pressure measurements

Findings (conti.)

• Tekscan Sensors -- technology developed for using them for track pressure measurements at the rail/plate and plate/tie interfaces – Sensors are thin and non-intrusive

– Repeatability is very good - consider loads applied, loading rate, and surrounding material

– Calibration is very important consideration

– Thin rubber bladder must be used on steel tie plates

– Shim stock is necessary

– Wide range of track related applications

Findings (conti.)

• Tekscan Sensors -- technology developed for using them for track pressure measurements at the rail/plate and plate/tie interfaces

– Sensors are thin and non-intrusive

– Repeatability is very good - consider loads applied, loading rate, and surrounding material

– Calibration is very important consideration

– Thin rubber bladder must be used on steel tie plates

– Shim stock is necessary

– Wide range of track related applications

Potential Tekscan Applications

• Superelevation – Curve design

• Impact pressures – diamonds

-- bridge approaches

• Plates, Pads, Fastenings & Ties

• ? ? ? ? ?

Acknowledgements