CRC Projects R3.106 and R3.117 studied ballast design and performance through laboratory testing and field trials. Integrated models were developed to assess track drainage, ballast breakage, and deformation using parameters like void contaminant index and plastic strain. Field trials showed geosynthetics and shock mats can improve performance of fresh and recycled ballast. A new design method called SMART systematically analyzes rail tracks based on critical shear strength and deformation criteria.

1. Cooperative Research Centre (CRC) for Rail Innovation
Showcase Event
Thursday 30 September 2010
Integrated Ballast–Formation-Track Design
and Analysis including the Implications of
Ballast Fouling and High Impact Loads
CRC Projects R3.106 - Ballast Design
Buddhima Indraratna
Professor of Civil Engineering
Director, Centre for Geomechanics & Railway Engineering
Faculty of Engineering, University of Wollongong
Other Researchers: Dr Sanjay Nimbalkar; Dr Cholachat
Rujikiatkamjorn, Nayoma Tennakoon (PhD student)
Industry Partners: David Christie and Sandy Pfeiffer (RailCorp); Mike
Martin and Damien Foun (QR), Tim Neville (ARTC)

2. Problems in Rail Track Substructure
Clay Pumping Differential Settlement
Void Clogging Degradation
Coal Fouling Poor Drainage

3. Ballast Fouling
Void Contaminant Index (VCI)
(1+ef) Gs.b Mf
VCI = x x x 100
eb Gs.f Mb
eb = Void ratio of clean ballast
ef = Void ratio of fouling material
Gs-b = Specific gravity of ballast material
Gs-f = Specific gravity of fouling material
Mb = Dry mass of clean ballast
Mf = Dry mass of fouling material
kb  k f
k
k f  VCI  (kb  k f )
100

4. Permeability Test Measurements and Predictions
1.E+00 kb  k f
k
k f  VCI  (kb  k f ) Clay fouled ballast-Theoretical
Hydraulic Conductivity /(m/s)
100
1.E-01
Coal fouled ballast-Theoretical
1.E-02 Clay fouled ballast-Experimental
Coal fouled ballast-Experimental
1.E-03
1.E-04 Hydrulic conductivity of
coal fines
1.E-05
Hydraulic conductivity of
clayey fine sand
1.E-06
0 20 40 60 80 100
Void Contaminant Index,VCI /(%)

5. Seepage model with SEEP-W
4m Total Head =0.5m
Zero pore water
pressure
0.3m
45 o
Clay fouled ballast
Degree of Fouling Hydraulic conductivity
VCI (%) k (m/s) – Lab data
Drainage Criteria – PhD work of Ms. Nayoma Tennakoon
0% 0.3
25% 0.02
50% 0.00012 Free Drainage Q/Qc>50
100% 2.3 x 10-8 Good drainage 5<Q/Qc<50
Acceptable drainage 1<Q/Qc<5
Equivalent Maximum Flow rate ,Qc = 0.4 litres/sec.
Poor Drainage 0.25<Q/Qc<1
(based on an extreme precipitation event of
300mm/hour) Very Poor 0.0005<Q/Qc<0.25
Drainage capacity of the track, Q
Impervious Q/Qc<0.0005

6. Track Drainage Assessment
Shoulder ballast maintenance
requirement
Shoulder
ballast with
0% VCI Shoulder
Shoulder ballast with
ballast with Shoulder ballast 100% VCI
25% VCI with 50% VCI
Poor
Drainage
Poor
(k2,k3,k4) Drainage
(k2,k3,k4) L=0.2m L=0.1m
Min. VCI =
(50,50,50)
Min. VCI =
(50,50,50) Poor
Drainage in
all cases Poor Drainage
(k2,k3,k4)
Min. VCI =
Top ballast layer k4
(25,25,25)
Middle ballast layer k3
Impervious in all
cases
Bottom Ballast layer k2
L
L

7. Performance of ballast upon impact – use of shock mats
Drop Hammer - Impact Testing equipment Weight of drop hammer = 5.81 kN (0.6 t)
Maximum Height = 6 m
Maximum drop velocity = 10 m/s
Dynamic load cell capacity = 1200 kN
Height of the ballast sample = 300 mm
Diameter of the ballast sample= 300 mm
Low confining pressures in track are
similar to rubber membrane encasement

8. Impact Response
Impact force excitation during 1st Blow Impact force excitation during 9th Blow
360 360
Fast Fourier Transform: Fast Fourier Transform:
Low Pass Filter (cut-off frequency 50000 Hz) 320
Low Pass Filter (cut-off frequency 50000 Hz)
320
280 280
Multiple P1 type peaks
240 240
Impact force (kN)
Impact force (kN)
200 Separation between the impactor and sample 200
160 160
120 120 P2 type peak
80 80
40 40
0 0
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18
time (sec) time (sec)
1st Blow 9th Blow
In the application of continuous blows on the same specimen, multiple
instantaneous P1 peaks are followed by a longer duration P2 peak.
It is force P2 that causes predominate ballast damage.
With greater breakage and subsequent compression, P2 peak
becomes more distinct with increasing number of blows.

9. Assessment of ballast breakage during impact
1 Subgrade Position of shock Ballast Breakage
d95i
A type mat Index (BBI)
BBI  A
dmax
B A B
Without shock mat
ge
ka
PSD = particle size distribution ea
br
Stiff - 0.170
Fraction Passing
2.36 = smallest sieve size
um
d95i = d95 of largest
im
ax
sieve size
Soft - 0.080
m
of
ry
With Shock mat
da
Shift in PSD
un
caused by
bo
degradation
Stiff Above ballast 0.145
ry
tra
bi
Ar
Stiff Below ballast 0.129
Initial PSD
0
Final PSD Stiff Above & below 0.091
2.36
0 Sieve Size (mm) 63 ballast
Indraratna et al., 2005 Soft Above ballast 0.045
Soft Below ballast 0.056
Soft Above & below 0.028
ballast

10. Use of Geosynthetics – Process Simulation Testing
Number of load cycles, N
0 100000 200000 300000 400000 500000 600000
0
Fresh ballast (wet)
Recycled ballast (wet)
5
Rapid increase Recycled ballast with geotextile (wet)
Settlement, S (mm)
in settlement
Recycled ballast with geogrid (wet)
10 Recycled ballast with geocomposite (wet)
15
20
Stabilisation
25
Settlement of ballast with and without geosynthetics
Grain size (mm)
0 10 20 30 40 50 60 70
4
Highest breakage
Effect of geosynthetics
Prismoidal Triaxial Rig to 2
Simulate a Track Section D Wk (%)
0
(Specimen: 800600600 mm)
-2 Fresh ballast (wet)
Recycled ballast (wet)
Recycled ballast with geotextile (wet)
-4
Recycled ballast with geogrid (wet)
Recycled ballast with geocomposite (wet)
-6
Effect of Geosynthetics on Ballast Degradation

11. From Theory to Practice: Use of Geosynthetics in Bulli Track
Details of instrumented track
Section of ballasted track bed with geocomposite layer

12. Preparation of Fully Instrumented Trial Track in Bulli
Geocomposite layer
(geogrid+geotextile)
before ballast
Ballast placement
placement
over the geocomposite 8 October 2006
Geotextile
Recycled Ballast Fresh Ballast
Bonded Geogrid
from Chullora Quarry, Sydney Bombo Quarry, Wollongong

13. Field Instrumentation in Bulli
Settlement pegs Displacement
installed at ballast- transducers installed at
capping interface sleeper-ballast interface

14. Deformation of Ballast
(Indraratna et al, ASCE, JGGE, 2010)
Number of load cycles, N Number of load cycles, N
5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5
0 1x10 2x10 3x10 4x10 5x10 6x10 7x10 8x10 9x10 0 1x10 2x10 3x10 4x10 5x10 6x10 7x10
0 0.00 -0 -0.00
Average lateral displacement of ballast, (S h)avg (mm)
Fresh Ballast (uniform graded) Fresh Ballast (uniform graded)
Average vertical strain of ballast, ( 1)avg (%)
Mean settlement of ballast, (S v)avg (mm)
Average lateral strain of ballast, 3)avg (%)
3
Recycled Ballast (well graded) 1.00
-2 Recycled Ballast (well graded) -0.08
Fresh Ballast with Geocomposite Fresh Ballast with Geocomposite
Recycled Ballast with Geocomposite -4 Recycled Ballast with Geocomposite -0.16
6 2.00
-6 -0.24
9 3.00
-8 -0.32
12 4.00
-10 -0.40
15 5.00
-12 -0.48
18 6.00 -14 -0.56
0 2 4 6 8 10 12 14 16 18 0 2 4 6 8 10 12 14
time, t (months) time, t (months)
Mean settlement (Sv)avg and Average lateral displacement (Sh)avg
average vertical strain (1)avg and average lateral strain (3)avg
The recycled ballast performs well, if a well-graded PSD is adopted (Cu = 1.8) and
stabilised with geogrids.
A well-graded recycled ballast (Cu>2) can provide a higher placement density, hence
a reduced settlement compared to a Uniform ballast (Cu<1.5) .

15. Use of Shock Mats & Geogrids in Practice: Singleton (NSW) – R3.117
Soft Subgrade: Embankment fill Stiff Subgrade: Hard rock cutting
Types of Geosynthetic
Biaxial Geogrid - TerraGrid TG3030 (Polyfabrics)
Biaxial Geogrid - Tensar Geogrid SSLA30
(Geofabrics Australasia)
Biaxial Geogrid - EnkaGrid MAX 30 (Maccaferri)
Geocomposite - Combigrid 40/40 Geogrid +
Geotextile (Global Synthetics)
Shock mat (10 mm thick)

16. Instrumented Track for Performance Monitoring - Singleton
Settlement pegs
Geogrid layer placed placement in the track
above the capping
Pressure cells below
the sleeper Mudies Creek Bridge
pressure cells installation

17. PLAXIS - Finite Element Analysis
Vertical stress under rail, v (kPa)
0 50 100 150 200 250 300
0
Depth below base of sleeper, z (mm)
150
Ballast layer
300
Sub-ballast layer
Elasto-plastic Model
Field Data
450
Ultimate redistribution of vertical stress
Settlement under rail, Sv (mm)
0 5 10 15 20 25 30 35
0
Depth below base of sleeper, z (mm)
Because of symmetry, adequate to consider half of the
150
track Ballast layer
Axle load of 25 tonnes and dynamic impact factor of
300
1.43 (@ speed of 80 km/h on standard gauge) Sub-ballast layer
Elasto-plastic Model
FEM predictions are underestimated because 450
Field Data
breakage is not captured well
Ultimate settlement with depth
If breakage is captured with associated plastic flow, then the settlement prediction will be more
accurate.

18. New Design Procedures – UoW method
(Systematic Method of Analysis of Rail Track – SMART)
Criterion 1: Critical Shear Strength (ballast or subgrade)
UOW
Conventional Li and Selig approach UoW Ballast Parameters

19. Criterion 2: Critical track deformation
(Plastic vertical strains for (a) ballast = 8%; (b) subgrade = 2%)
UOW
Conventional Li and Selig approach UoW ballast parameters

20. Single Subgrade Layer Formulation of Multiple Subgrade Layers
SMART Approach
(to be completed in 2012
under R3.117 project)

21. Conclusions
• The track drainage is assessed using a new parameter, ‘Void
Contaminant Index’ - VCI that takes into account the specific gravity of
different fouling materials.
• Recycled ballast stabilised with Geosynthetics can perform as well as
fresh ballast
• Shock mats improve the performance of ballast by reducing the
breakage caused by impact loads. Effectiveness depends on the
subgrade stiffness.
• Field trials conducted in Bulli and Singleton (NSW) demonstrate the
advantages of Field Performance Monitoring, apart from calibrating
FEM-based design technique.
• UOW research outcomes are continually captured in a MATLAB based
design approach: SMART (Systematic Method of Analysis of Rail
Tracks).

22. Acknowledgement
 Australian Research Council (2 Discovery Projects and 3 Linkage
Projects since 1993).
 Cooperative Research Centre for Railway Engineering and Technologies
(Rail CRC) (Project 6/139) from 2000-2007
 Cooperative Research Centre (CRC for Rail Innovation)
 ARC Centre of Excellence for Geotechnics (funded in 2010).
 Industry Partners:
RailCorp, QR, and ARTC.
 David Christie (RaiCorp, Sydney)
 Tim Neville (ARTC, Newcastle)
 Michael Martin, Damien Foun (QR, Brisbane)
 Sandy Pfeiffer (RaiCorp, Sydney)
 UOW Researchers: Dr Joanne Lackenby, Dr Wadud Salim, Dr. Sanjay
Nimbalkar, Ms. Nayoma Tennakoon, Dr Cholachat Rujikiatkamjorn
 UOW Technical Staff: Alan Grant, Cameron Neilson, Ian Bridge

24. Test materials – Specifications
Material Particle dmax dmin d50 Cu 100
Shape (mm) (mm) (mm)
90
Fresh Highly 63.0 19.0 35.0 1.6
Ballast angular 80 Sand
Subgrade - 4.75 0.075 0.48 2.3 70
(sand) Fresh Ballast
60
% passing
50
40
Australian Standard
30 AS 2758.7 (1996)
20 UoW new gradation
Indraratna and Salim (2005)
10
0
0.010 0.100 1.000 10.000 100.000
Particle Size (mm)
Fine sand as subgrade
Shock mat (10 mm thick)
made of recycled rubber
(polyurethane)
Damping Ratio = 0.08

25. Multiple Impact Loading with Shock Mats
Number of blows, N Number of blows, N
0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10
52 52
No Shock mat
48 48
Shock mat at top
Maximum Impact Force, P 2 (kN)
Shock mat at bottom
Maximum Impact Force, P2 (kN)
44 44
Shock mat at top and bottom
40 40
36 36
32 32
28 28
No Shock mat
24 Shock mat at top 24
Shock mat at bottom
20 Shock mat at top and bottom 20
0.0 0.6 1.2 1.7 2.3 2.9 3.5 4.1 4.6 5.2 5.8 0.0 0.6 1.2 1.7 2.3 2.9 3.5 4.1 4.6 5.2 5.8
Cumulative Impact Energy, E (kNm) Cumulative Impact Energy, E (kNm)
Very Stiff Subgrade – steel plate Natural Softer Subgrade - sand
The P2 force shows a significant increase with the extent of cumulative impact energy.
For stiff subgrade, shock mat is more effective in reducing P2 when located at the
bottom of ballast than at the top.
A soft subgrade itself serves as an energy absorber, hence the benefits of the shock mat are
generally marginal. However, if the shock mat is placed at the top of ballast to attenuate the
impulse waves, then P2 is reduced (less breakage).