1. The Influence of Ballast Fouling on Track Settlement
A Rampersad, TB George, R Mokoena, MB Mgangira and PJ Gräbe
37th Annual Southern African Transportation Conference,
Pretoria, South Africa, 9 – 12 July 2018
Presented by Ashiel Rampersad

2. Outline of Presentation
Background and Objectives
Literature Review
Material characterization
Test Program (Box Testing)
Results and discussions
Conclusions and recommendations
Acknowledgments
CSIR
University of Pretoria

3. What is Ballast Fouling?
Ballast fouling refers to the changing of composition of the ballast layer and becoming a much finer grain size distribution.
Fouling commonly occurs due to the degradation or breakage of ballast aggregates.
Contamination of ballast could also result from cargo material spillages such as coal dust/fines

4. Background
Over R200 billion has been allotted to the South African Railway industry to expand its rail infrastructure in order to create capacity and to increase cargo volumes.
The increase in future rail demand will result in an increase of coal, iron ore and general freight rail capacity by 44, 57 and 113 % respectively.
This increase in railway capacity will render the supporting track materials to more frequent cyclic loadings, leading to the degradation of ballast particles.
Current local practice is to use a visual assessment score (rated as new, good, fair, poor, unserviceable) to assess the condition of ballast.
There are currently no standards for a critical level of fouled ballast for which maintenance should occur.

5. Objectives
To relate the track settlement with the degree of ballast contaminated with coal dust using a large scale box test apparatus.
To identify a critical level of contamination in which ballast maintenance should be done.
MTS® Hydraulic Actuator

6. Literature Review
Limited research relating ballast fouling and track settlement in a South African context.
Ballast Breakdown and Grading
Selig & Waters (1994) showed that ballast breakdown accounts for the majority of fouling material (76%) followed by infiltration of sub-ballast (13%).
Anbazhagan et. al. (2012) reviewed the impact of ballast gradation as a form of fouling. It was found that poorly graded ballast is more favourable for drainage but may not be favourable for stability and settlement.
Box Testing (Settlement)
Han & Selig (1997): Box tests – settlement increased rapidly for wet clay for percentages above 20%.
Kashani et al. (2017) studied the effect of fouled ballast and moisture content on plastic settlement of ballast under cyclic loading. A 3% increase in water content quadruples the rate of settlement (15% fouled).

7. Literature Review Shear Strength
Huang et. al. (2009): Direct Shear Box - 15% of dry coal dust and 25% of wet coal dust (OMC) showed the highest reduction in shear strength. Identified the loss of contact between ballast particles (affecting ballast strength and track stability)
Qian et. al. (2014): Large Scale Triaxial Testing - Permanent strain doubled at Fouling Index of 40 when compared to clean ballast.
Critical ballast phases: clean, partially fouled and heavily fouled

8. Material Characterization
Railway Ballast
Crushed Quartzite (Afrisam Ferro quarry)
Characterized according to Transnet S406 (1998) specifications
Ballast grading compared to Transnet specifications (1998) for heavy haul lines

9. Transnet S406 specification (1998)
Material Characterization
Railway Ballast (Continued)
Material physical properties of ballast
Parameter
Ballast result
Test method / Equation
Transnet S406 specification (1998)
ACV Dry
21.6
SANS 3001 AG10
None
10% FACT Dry (kN)
181
Flakiness Index (%)
8.1
SABS 1083
≤ 30 %
LA Abrasion (%)
23.0
ASTM C131
≤ 22 %
Mill Abrasion (%)
5.7
Transnet S406
≤ 7 %
Soundness (%)
4.3
ASTM C88
≤ 5 %
Percentage voids
43.8
≥ 40 %
Void ratio
0.78 -
Relative density
2.632
SANS 3001 AG20
≥ 2.5
ACV: Aggregate crushing value, FACT: Fines aggregate crushing test, LA: Los Angeles

10. Material Characterization
Fouling Material
Coal dust obtained from Anglo-American Coal Plant
No standards for comparison of the fouling material
Coal Dust Material Properties
Parameter
Test Method / Equation
Coal Dust Result
Bulk density (kg/m3)
TMH 1 Method B9
770
Bulk relative density
SANS 3001 AG21
1.83
Void content (%)
ASTM C1252
57.8
Void ratio
1.37

11. Material Characterization
Fouling Material
Analysis using Scanning Electron Microscope (SEM)
SEM images showed equant, irregular and discoidal shapes
Particles are of medium sphericity between angular and round
200 x
500 x
1 000 x x

12. Material Characterization
Fouling Material
An Energy Dispersive X-ray Spectroscopy (EDS) image shows the distribution of elements on the particle
Predominant elements: Carbon, oxygen, silicon and aluminium
Iron, calcium, potassium and sulphur were detected in lower quantities
Combined layered image of Coal Dust (EDS)

13. Material Characterization
Sample Preparation
Ballast
Washed and dried to remove fines
Quartered to obtain a representative sample (SANS 3001)
Box Test
Loaded in three layers, compacted using a tamping rod (AASHTO T19)
Coal dust placed above the bottom layer at 5% moisture (to simulate the first wash of fines)
Coal dust
Quartering of ballast

14. Box Test
Schematic diagram
Box test setup

15. Box Test Use of under sleeper pads (USP) Used USP Unused USP
Placed between the concrete block and ballast
Provides increased load spread through the sleepers onto the ballast
Reduction in stresses within the ballast layer
Contributes to the reduction in ballast breakdown and settlement (Gräbe, 2016)
Used USP
Unused USP

16. Box Test Quantification of the degree of fouling Fouling Index (FI)
Percentage Void Contamination (PCV)
Feldman and Nissen: Parameters needs to be calculated after compacting the fouling material. Does not accurately represent field conditions.
Fouling Index (FI)
Misinterpretation of the actual degree of fouling if materials with significantly different specific gravities were used.
Void Contamination Index (VCI)
e b / f = Void ratio of clean ballast / fouling material
G sb / sf = Specific gravity of clean ballast / fouling material
M b / f = Dry mass of clean ballast / fouling material

17. Box Test Performance Testing Initial settlement Final testing
Metal Box: 500 x 500 x 200 mm
Concrete block: 200 x 150 x 150 mm
MTS® hydraulic actuator
Applies a continuous cyclic load with no rest period on the ballast
The piston with a loading plate pushes down onto the concrete block
The Linear Variable Differential Transformer (LVDT) sensors measure the vertical displacement
Initial settlement
A vertical load of 6 kN at 10 Hz frequency for cycles
Initial testing at 20 Hz showed excessive vibrations
Final testing
A vertical load of 13 kN at 10 Hz frequency for cycles
These conditions simulate a 26 tonne axle on the ballast (typical heavy haul line in South Africa)
Results were sampled at 100 Hz

18. Ballast Settlement Results
Large Scale Box Test (Settlement results)
Quantify the effect of fouling material (coal dust) on the rate of settlement of ballast
The settlement increases with an increase of fouling (VCI)
The sudden dips in the settlement can be attributed to the movement and breaking of the individual ballast particles
Box test settlement of fouled ballast

19. Ballast Settlement Results
Large Scale Box Test (Settlement results)
The results show an increase in settlement of between 11.7 and 40.2 % VCI per 10 % increase in coal contamination.
The critical limit of 25 % VCI is noted as the point of change in gradient.
Total settlement per VCI of fouling

20. Ballast Settlement Results
Rate of ballast settlement and breakage / movement points
Provides an indication of rate of settlement and the occurrences (at cycles) of ballast breakage / movement
Gradient of settlement
Average settlement: ≈ cycles / 1 mm settlement
Closeness of data (Coefficient of Variation): Standard deviation / Mean = 36%
Ballast breakage / movement
Most frequently at beginning of test
Rate of ballast settlement and breakage / movement points
VCI (%)
Gradient of settlement
Ballast breakage / movement occurrence (at cycles)
1 mm settlement per x number of cycles
Observed between cycles
40 000
20 000 and
≈ 8 000 and
8.4
20 000
60 000 and
≈ 0 to 8 000 and
16.9
60 000
≈ 0 to 10 000 and 22 000
25.3
35 000
30 000 and
≈ 0 to
33.8
30 000
20 000 and
≈ 0 to 18 000

21. Conclusions
The material characterization and the response of fouled ballast in terms of settlement has been quantified in this study
It is noted that there has been no previously published results relating ballast fouling to track settlement in a South African context.
The following conclusions can be drawn:
The influence of fouled ballast does have a significant effect on track settlement
Results indicated an increase in settlement of between 11.7 and 40.2% per 10% increase in coal contamination for a VCI up to 33.8%. The results are based on ballast samples with 5.0% moisture content.
The study does not generalize track settlement for all aggregates and fouling materials but focusses only on quartzite and coal dust respectively.
The results of the study pertain to only specific materials and gradings, as well as to specific test conditions that have been applied.

22. Recommendations
The study has confirmed that for quartzite ballast fouled with coal dust, the track does settle with an increase in fouling content.
The study is a work-in-progress and it is recommended that further research is done to address the following:
The use of alternate ballast and fouling materials to broaden the scope
The use of varying moisture contents
To incorporate track instability limits to determine the VCI in which maintenance is to be done

23. Thank you
Questions?
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