Degradation of the railway track ballast layer
Different ballast contamination indexes
P4 - % of particles passing the No. 4 sieve (4.75 mm)
P200 - % of particles passing the No. 200 sieve (0.075 mm) by weight
Fouling Index
eb - void ratio of clean ballast
ef - void ratio of fouling material
Gsb - specific gravity of clean ballast,
Gsf - specific gravity of fouling material
Mb - dry mass of clean ballast
Mf - dry mass of fouling material
Void Contaminant Index
Percentage Void Contamination
Bruzek et al., 2016
V1 - void volume between clean ballast particles (>9.5 mm) for a
given density and
V2 - total volume of fouling material (<9.5 mm) that fills V1
Hesse et al., 2014
Wenty_2007
As the percentage of fouling in the ballast increases, more water is retained by the fouled layer, resulting in track
instability due to the buildup of pore water pressure, as well as alignment problems. (Parsons et al., 2015)
Example of the effect of decreased ballast permeability due to contamination
Paiva et al., 2015
Selig, E. and Waters, 1994
Influence of the type of fine particles on the permeability of contaminated ballast
The results of some studies show that sand does not significantly influence the permeability
of the ballast, contrary to what happens with clay and silt. (Wallace, 2003)
Parsons et al, 2012
Fines from ballast crushing
Clay
It is important to consider the different ways of accounting for contamination, as they lead to
different conclusions.
% of contamination – ratio between the dry weight of the material
passed through the 9.5 mm sieve and the
dry weight of the total specimen
Fouling Index
The effect of % clay contamination on ballast permeability and rail operation
Tennakoon et al., 2014
25t/eixo
Shear strength
Considering
load dynamic
coefficients
where qpeak,b and qpeak,f are the peak deviator
stresses for fresh and fouled ballast respectively,
b is an empirical parameter dependent on s’3.
30t/eixo
Effect of water content and foundation soil compactness on material pumping
(Duong et al, 2014)
Monotonic and cyclic load
N=500 000 ciclos
w=16%; rd-inicial=1,4Mg/m3
•In the unsaturated state, settling occurred on the ballast and sub-ballast, but no fine
particle migration occurred.
Effect of water content and foundation soil compactness on material pumping (cont.)
(Duong et al, 2014)
•In the saturated state, the ballast/soil interface rises and the level of “pumping”
depends on the initial dry weight of the soil:
for the initial value of ρd = 1.6 Mg/m3, for the initial value of ρd = 1.4 Mg/m3 and
only interpenetration between ballast 1.5 Mg/m3 soil liquefaction occurred
and soil occurred, resulting in under cyclic load. The excess of pore
contaminated ballast.
pressure dissipated, causing pumping.
N=500 000 ciclos
w=saturated; rd-inicial=1,6Mg/m3
N=500 000 ciclos
w=saturated; rd-inicial=1,4Mg/m3
Evaluation of fine pumping
deterioration
Nguyen et al., 2019
Kuo, 2017
Solutions to avoid pumping
prefabricated vertical drains (PVDs)
Nguyen et al., 2019
Solutions to avoid pumping
Nguyen et al., 2019
Influence of the type of contamination on the permanent deformation of new and
recycled ballast
Gso = 2.6 (Gs of mineral fouling)
Gs = specific gravity of the specific fouling material.
FC – Fouling content
FI – volumetric Fouling Index
Large-scale cyclic triaxial tests
Ebrahimi et al., 2015
Cyclic Triaxial Test
Contamination with non-plastic soils
Fouled
recycled
ballast
Fouled fresh
ballast
For low values of w,…
Contamination with plastic soils
Ebrahimi et al., 2015
CFI - cohesive fouling index
FC - fouling content
CMI - cohesive-fouling moisture index
The permanent deformation of
the ballast depends on:
 fines content
 plasticity of fines
 water content
Shear strength of ballast
contaminated with fines
from its own
degradation (LA test)
FI=40
Triaxial tests to
determine shear strength
in contaminated ballast
Influence of water content of fines
Qian et al., 2016
Ballast with dry
fines
• Ballast contaminated with
dry fines has similar or better
strength than clean ballast.
• Strength decreases with
increasing water content of
the fine contamination
material.
Influence of contamination and water on permanent settlement and deflection
evaluated in a railway track physical model
(Ishikawa, 2016, adaptado)
Physical model in true scale
Permanent settlement
before wetting
Deflection
after wetting
before wetting
after wetting
Influence of the % contamination of the ballast with sand on the forces on the sleepers
(Kian et al., 2020)
Percentage of fouling (contamination) = contamination index = ratio of the dry weight of the particles smaller than the
9.5mm to the dry weight of the sample
+
+
Decreased
strength and
stiffness with
increasing
contamination
Estimation of forces on
the sleepers as a function
of the % of ballast
contamination
Mc – bending moment at the center of the sleeper
bc – sleeper width at the center of the sleeper
Mr –bending moment at the rail seat position
br – sleeper width at the rail seat position
L – sleeper length
g – track gage
Q – static wheel load
DF, a1 and a2 – obtained from the figure.
j – dynamic amplification factor
u – track modulus
s – sleeper spacing
EI – rail flexural rigidity respectively
Ballast in poor condition requires high maintenance resources.…
standard deviation of longitudinal levelling defects
Strange, 2008
Rehabilitation of the ballast layer
Mechanical removal and cleaning of the ballast, followed by placement of an
adequate layer thickness with good quality material.
Comparison of annual maintenance costs per
km of track, with and without ballast cleaning
(Wenty, 2003, adaptado)
Tamping
Manual tamping
Milne et al., 2018
Loose ballast
Voids
Compacted material
Tamping
Khouy, 2014
Tamping
• Due to railway track maintenance works, the following may occur:
Change in granulometry of ballast
Reduced lateral resistance of the track
decrease in geometric quality
Improved track geometric quality due to tamping, for excellent substructure, good and bad
decrease in geometric quality
Khouy, 2014
Study of the effects of the tamping on ballast breakage
Perales et al., 2011
• 34 ballast big-bags between 300 and 500 kg each
• Under to a distinct number of tamping actions (0 to 45)
Conclusions:
• The most affected particles are those with D > 50mm
• There is an increase of particles in the 35.5 to 50 mm
fraction
• The proportion of fine particles did not exceed 0.38%
per big-bag
• Minimum penetration speed of the equipment is less
aggressive than normal and maximum
• Tamping does not cause statistically significant wear
in terms of loss of angularity
D=50mm
Ballast deformation with varying degrees of contamination subject to tamping
Micro-ballast
Displacement vectors for new ballast before and after tamping
(Kumara & Hayano, 2016)
Ballast deformation with varying degrees of contamination subject to tamping (cont.)
(Kumara & Hayano, 2016)
Inflection point
Improvement
the trend is similar in both cases
Triaxial tests - shear strength
Residual settlement rate
the curves are similar to each other
Tamping is more efficient on clean or lightly contaminated ballast
Comparison of tamping effect durability in different situations
Strange, 2008
• The durability of the appropriate track geometry is maintained, in
the best cases between 7 and 12 years, and in the worst cases only
1 year.
• In UIC networks there is no reasonable correlation between the
durability of the track geometry, resulting from the tamping, and
the operation speed or the volume of freight.
• This is probably due to the differences related to:
Railway track construction quality
Quality and level of maintenance
Tamping methodology
Maintenance frequency
Dynamic track stabilization
(Dynamic Track Stabilizer - DTS)
Continuous measurement of lateral displacement
resistance before and after the tamping and after DTS
Becker, 2007
DGS 62 N
Dynamic Track
Stabilizer
“There is no significant advantage in using the DTS or crib/shoulder consolidators to
improve track geometry durability.”
• Therefore there would appear to be no maintenance
tamping durability benefit from the use of the DTS or the
special crib/shoulder consolidators; the rates of
deterioration are all quite similar. Any slight increase in
durability would only be of benefit if an entire tamping
cycle could be saved in LCC. The graphs suggest that
this would be unlikely.
• The real use of consolidation and DTS is for improving
initial lateral stability after maintenance tamping and to
Strange, 2008
avoid speed restrictions.
However, there are other studies that demonstrate some contribution of DTS to
delay the degradation of long-term longitudinal leveling.
Comparison of track geometry evolution with and without dynamic stabilization
Aliakar, 2012
“Ballast injection” (Stoneblowing) (UK)
Will it be an alternative to the conventional tamping?
Note: This information is provided by
the equipment manufacturer.
This technique is perhaps more suited to solving specific problems, after assessing the situation.
The Multipurpose Stoneblower is a revolutionary machine developed specifically as an
alternative to traditional tamping methods for the restoration of the track’s vertical and
lateral alignment.
Harsco Rail, 2013
Harsco Rail, 2013
Harsco Rail, 2013
Zarembski & Newman, 2008
The machine utilizes a process which pneumatically injects ballast under the sleeper to
achieve a track position accuracy without disturbing the pre-existing compacted
formation. The result is a smooth track surface which can be immediately available for
unrestricted line speeds.
The machine has undergone extensive testing to meet demanding requirements and has
demonstrated the ability to significantly extend the time required between track
maintenance cycles. (Harsco Rail, 2013)
Desvio padrão
do nivelamento
longitudinal(mm)
standard
deviation
of longitudinal
levelling defects
Tamping
Stoneblowing
LTN1 1100 79.0660-79.0880
LTN1 1100 55.0880-55.11000.01.02.03.04.05.001
Degradation of Track after Stoneblowing: Network Rail Norwich
Line (LTN1 1100) 2007-2008 Data
Degradation of Track after Tamping: Network Rail
Norwich Line (LTN1 1100) 2007-2008 Data
Track Quality Index - track quality assessment
(qualidade aumenta com a redução do TQI)
Best performance
Zarembski & Newman, 2008
Harsco Rail, 2013
Zarembski & Newman, 2008
After stoneblowing, the track is immediately opened at the line of speed, and tests have
shown that the track remains in position on average, four times longer than track
maintained by traditional tamping methods.
Strange, 2008
Application in transition zones with bad behavior.
Calculated values (mm)
Boler et al., 2019