A THEORETICAL MODEL OF
BALLAST FOULING
de Paiva, Cassio E. L.; PhD, Professor
Peixoto, C. F.; MsC, Professor
UNICAMP - State University of Campinas
Brazil
INTRODUCTION
• Oldest Brazilian railways are frequently
located near or on the river edges, where flat
terrains are observed but subjected to
frequent flooding.
• The ballast built on these areas probably
makes more demands on cleaning ballast
work, to remove soil particles clogging voids
which modifies track behaviour and reduces
permeability coefficient.
INTRODUCTION
• The stresses and strains developed from track
loads and spread to ballast, sub-ballast and to the
sub-grade can be affected by the clogging action,
changing layers system behaviour.
• The main objective of this recherche is to show
and to discuss the used math models to study
fouled ballast under hydraulic and subterranean
theorems.
• It is proposed a special model to predict water
flux inside ballast, the McLelland Box modified
according to this distinguished medium.
BALLAST FOULING SOURCES
• Ballast fouling occurs under a group of effects.
• There is an internal group of effects which produces
small particles from the standard ballast:
– the dynamic traffic efforts and tamping ballast.
– the external events can be grouped into seepage
action and wind as a carrier of soil particles to the
interior of the ballast.
• The main railway features which contribute to ballast
fouling are: sleeper wear, particle migration, ballast
tamping as a function of repeated load, slurry and
hydraulic action.
Seepage or superficial drainage also carries solid
particles to the ballast voids
Platform cross section
Ballast and subgrade interface
carrying soil particles to the
crushed stone
Subterranean drainage system
subgrade seepage network
Oldest railway tracks
Railways crossing desert areas are subjected to
wind carrying fine soil particles
Wind carrying fine sand particles
Clogging path by wind
The real situation of the freight
railways in Brazil
• In the nineties, by a governmental decision,
almost all Brazilian freight railways are under
private concession, because of the absence of
resources to keep railways working and also to
minimize management difficulties.
• Until today, Brazilian Railway Dealers did not
achieve budget surplus to start a massive
maintenance program.
The real situation of the freight
railways in Brazil
• The Brazilian Concession Model does not guarantee
enough funds for the railway maintenance.
• So, it is common to see just ballast maintenance
instead of rails and sleepers changing.
• Putting more crushed stone on the ballast to level the
track is one of the most frequent maintenance activity
applied on them.
• Dealers focus on the waggons and locomotives
purchase than investing money on the track
maintenance because if they decide to break up the
contract they will have to leave all equipments applied
on the track.
IMPORTANCE OF BALLAST CLOGGING
TO THE RAILWAY MAINTENANCE
• A high extension of them crosses large areas
subjected to high level of precipitation,
resulting in higher ballast moisture and fouling
through seepage.
• It is necessary to develop new maintenance
techniques under more precise math and
physics approach in order to understand
better the relationship between ballast
clogging and track behaviour.
IMPORTANCE OF BALLAST CLOGGING
TO THE RAILWAY MAINTENANCE
• The ballast cleaning service can be planned
according to the forecasted time to clog
ballast voids.
• The speed of water at the seepage is an
important quantity for service management.
• The difference between the forecasted water
speed and the real one is subjected to the
seepage adopted regime.
THEORETICAL MODELS OF CLOGGING
BALLAST WATER FLOW
• This recherche is in its first phase.
• Its beginning was based in the work of
Peixoto’s Master Degree dissertation (1988);
• The seepage through porous media needs, to
be considered as a proportion of hydraulic
gradient, and validating the permeability
coefficient must analyzed by Equations A or B,
according to the researches of Peixoto.
THEORETICAL MODELS OF CLOGGING
BALLAST WATER FLOW
0.42
ici  2  0.182
D10
(A)
Equation A gives the inferior limit of hydraulic gradient,
for compacted samples, guarantying the flux as a laminar
one.
The granular material researched presents effective
diametre from 0.1 to 5 mm, i.e., the diametre of grading
curve at 10 % passing, possibly shown at fouled ballast.
In this case, it is proposed to enlarge this research to
bigger diameters, as a cleaned ballast in general shows.
THEORETICAL MODELS OF CLOGGING
BALLAST WATER FLOW
• Equation B gives the same limit but for non
compacted samples, all the other features kept
equal.
ici 
0.098
 0.008
2
D10
(B)
Ici: hydraulic gradient for tamped samples (m/m);
D210: effective diameter (mm) of non compacted
samples
Proposed Dynamic Drainage Clogging
Ballast Model
Ballast seepage
pumping
Dynamic load
(hammer effect)
Ballast equipotencials and
flowlines
Gap to the studied
displacement
Proposed Dynamic Drainage Clogging
Ballast Model
• During ballast lifetime a huge amount of dynamic loads
subjects sleepers like a hammer on the ballast top.
• After several load actions some sleepers can show a
gap between its bottom surface and ballast top.
• During flooding period, this gap can work as a piston
due to the trains frequency, pumping water and
subgrade soil particles to ballast media voids.
• This scenario is represented at previous figure, which
pictures the moment when the train acts on the rails,
the sleeper settles and the gap diminishes. Then, just
some seconds after, the sleepers return to its previous
level, pumping water and soil particles.
PHYSICAL MODEL AT NATURAL SCALE
OF BALLAST SEEPAGE
• It was conceived a physical model to reproduce
soil water seepage considering transient flux by
McClelland (1943), a single model which permits
to predict and to evaluate water table in two
dimensions in natural scale into a ballasted box.
• It is highlighted that this model focuses transient
flux study, not permanent one, describing the
variation of water table level during the flux
changing according to a special rain, taken as a
representative one.
PHYSICAL MODEL AT NATURAL SCALE
OF BALLAST SEEPAGE
• McClelland aimed to study the transitional
flux, but, in this approach, it is proposed to
evaluate also ballast clogging, under the solid
and water flux controlling, measuring
clogging, permeability coefficient, strain and
stresses variation.
PHYSICAL MODEL AT NATURAL SCALE
OF BALLAST SEEPAGE
• It is proposed an adjustment to the McClelland
Box, as shown at figure ahead, where the charge
of water would be calculated to guarantee the
adequacy of Darcy’s Law.
• The water tankers of both sides were installed to
allow measurements of water density according
to Stokes Equation, for indirect estimation of the
amount of soil particles left inside the ballast.
• This test would evaluate the variation of
permeability coefficient and the fouling action to
the voids in function of time.
PHYSICAL MODEL AT NATURAL SCALE OF
BALLAST SEEPAGE
Symetrical platform axis
1,35
1,05
Pressures gauges (1 a 5):
1,20
1,20
D
siphon
W/2
S
Flexible
connetion
D variou
de 45 cm a
135 cm
W/2
from
120 cm
to 240
cm
Perforated
drain
6,00
(no scale)
1,20
0,45
ballast
1,80
Water source
Geotextil
screen
0,45
S was
abort
10 cm,
15 cm
and 20
cm
0,45
0,45
0,60
(m)
Adjusted McClelland Box to evaluate ballast transitional
flux and clogging
PHYSICAL MODEL AT NATURAL SCALE OF
BALLAST SEEPAGE
• After this first test, it is proposed to install a
sleeper part on the ballast top and to start
again these tests, with a cleaned ballast
tamped and graded the previous one.
• In this case it is intended to evaluate the
variation of permeability coefficient and
clogging voids in function of time, influenced
by crushed stone breakdown.
PHYSICAL MODEL AT NATURAL SCALE OF
BALLAST SEEPAGE
• In the next phase of tests, it will be evaluated the
influence of tamping and water carrying soil particles.
With the resulted curves it is possible to help better
maintenance planning.
• In the last phase of tests the water source will vary
during the time, allowing evaluation of the influence
transitional flux ballast fouling.
• It is intended to adopt a time which lasts a specific
strong rain, to calculate the amount of fines inside the
ballast just after a single strong rain.
PHYSICAL MODEL AT NATURAL SCALE OF
BALLAST SEEPAGE
• The ballast fouling behaviour and its lifetime
demand more researches to achieve new
models to conceive better planning ballast
maintenance under low costs.
• A natural or greater scale model of ballast and
subgrade system subjected to a controlled
seepage, according to the ambience
conditions helps to achieve this goal.
PHYSICAL MODEL AT NATURAL SCALE OF
BALLAST SEEPAGE
• In this case, it is proposed to apply the
McClelland Model Box, permitting to control
these quantities and to evaluate the ballast
coefficient in relation to the outline structure
changing as a function of the amount of solid
particles clogging the voids.
Thanks for your attention