Task Solutions -Railway Infrastructure Design and Management- SEV254

Task Solutions -Railway Infrastructure Design and Management- SEV254

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Reliable rail track infrastructure is the aim of the structural design of the track system. Every
decision arrived at during the design phase of the track has effects on the reliability in the use of
the infrastructure. During the structural design of the track, weighing of the trade -offs is done
between the initial cost and the robust design.
Ballasted railway tracks are mainly composed of two major components including the
substructure and the superstructure. The main components adopted in the constructi on of the
railway track include steel rails, granular ballast, different rail fastener types, timber, concrete or
even steel sleepers, subgrade materials besides sub -ballast. An understanding of the structural
behavior of track has historically being fac ed by various challenges (Sol -Sánchez et al., 2018 ).
This has been attributed to the various mechanical features of the components of the track from a
side and sophisticated interaction between the components of the track on the other. Broad range
of confi gurations of the track system can be constructed and design. As such the railway track
structure is subjected to constant changes. In the end, basis of the experimental and theoretical
investigations, greater number and other times conflicting design crite ria have been proposed by
various railway practitioners and authorities. The variations in the design criteria often renders
the process of structural design of the track a challenging undertaking.
This study focuses on the structural design of the railwa y track presented in the cases study. The
design of the railway track systems is aimed at offering smooth as well as safe running surface
for the moving trains. They as well aid in sustaining the imposed loads to the track structure
mainly due to passages of the train and changes in the temperature. In this task, an analysis and
design procedure is conducted for every element as a single and individual structural unit of the
railway track systems since there are quite large variations in the structural elem ents that have
been used in the railway track systems (Chen et al., 2018 ). With this approach, the interaction
between the components of the railway track systems are subsequent included via definition of
the appropriate boundary conditions alongside the t rends of load transfer.
Still, as the dynamic response features of the track tend not be understood adequately for
formation of a rationale design method, the current railway track systems design practices are
mainly dependent on relation of the noted dyn amic response to an equivalent static response.
Design analysis
Track loadings
The track serves as an elastic and load distributing structure. The distribution of loads is
influenced by the flexibility and stiffness. The distribution function may be show n roughly
through making an assumption of 30000 lb. when loading being placed on the rail. The contact
area will be at most 0.5 square and as such the stress in the rail would be 60000 psi. If the
subgrades are reasonably firm, they might be having a20 psi supporting capacity. The 60000 psi
stress has to be reduced or distributed by the track structure to not more than 20 psi. If this is not
achieved, the subgrade is likely not able to adequately support the train (Loktev et al., 2020 ).
The rails, in effec ting such distribution, act to absorb and distribute the loads in the wheel to the
ties with limited unit pressure, the loads will be distributed to the ballast by the ties and the load
is distributed from the subgrade to the natural ground by the subgrade .
Track Superstructure Design
The superstructure is in railway design is tasked with absorption of the horizontal and vert ical
forces as a result of the traffic load and transferring the same to the subsoil . The forces
distribution over to the larger areas leads to a distribution of load that aids in the prevention of
overstressing and overloading of each of the individual components of the superstructure and
makes sure the pressure of the surface on the subgrades is substantially low and uniform to t he
greatest attainable levels (Izvolt et al., 2021 ). Two basic designs are noted in a railway
superstructure including:
Ballast track; and
Ballastless track
These two kinds of superstructure shared in common the fact that the contact between the track
and the vehicle is attained via two rails. The rails are elastically held on the ties or sleepers or
even supported with the aid of rail fastening elements. There tend to be unique forms in tram
constructions where other rail fixation forms are used.
Ballastl ess track
Also known as the loading -bearing slab track system, the ballastless track system is a derivative
of its fixed and stable position. The principle of design for the case of the ballastless track system
is composed of each of the base layers with reducing stiffness from the top downwards.
ï‚· Rails
ï‚· Fastening elements
ï‚· Sleepers or ties
ï‚· Asphalt or concrete la yer
ï‚· Hydraulically bound layer
ï‚· Anti -freezing layer
Ballastless track systems are groups onto types having continuous support a swell as types
having support point support depending on the rail support system. Using sleepers can as well be
dispensed complete ly owing to the concrete supporting layers stability. In such a case, support in
attained in the rail using prefabricated supporting points or even directly fastened to the base
course (Ferdous et al., 2021 ). In as much as the fraction of ballastless track system tends to small
in the cumulative line length, it is noted to be gaining popularity and significance especially in
high speed traffic. Such is attributed to the permanently stable track position of the system.
Ballast was initially selected as rail way infrastructure basis as a result of its good mainten an ce
options as well as availability. This component is however currently the one noted to be limiting
the service life of the complete system. The sleepers and rails wear was the one used in
determining the complete system replacement, a situation that has since then changed with the
increased useful life to ballast (Sadri et al., 201 9).
The negative effect of ballast on track service life resulted in the initial design attempts of the
ballastless track. The ballast is substituted with concrete or asphalt sub -layers which minimal or
zero plastic deformation as opposed to ballast. The conscious application of elastic com ponents
is used in compensation of these layers elasticity. This is the only way through which the
necessary deflection can be attained of the track as well as the resultant distribution of the load
on various points (Loktev et al., 2018 ).
Ballasted superstructure
The ballasted superstructure is as well -known as the classic superstructure since it is representing
the superstructure largest proportion historically in Europe and has been applied in similar
elementary con cepts from the earliest days of the railway . It is made up of the following major
components :
ï‚· Protective layer
ï‚· Fastening components
ï‚· Sleepers or ties
ï‚· Ballast bedding
The laying of the sleepers in the ballasted superstructures is generally done in a transversal
manner to the track axis at 600mm, 650 mm or even 850 mm intervals. There are various types
of sleepers or ties that may be different in additives, construction and material. Excellent position
stability as well as optim um distributing of the load is attained through embedding sleepers
within a conglomerate of ballast stones.
The worth of the cross sleeper track laid in the ballast has been proven since the railway age
beginning and is used in the representation of the r ailway superstructure standard form. The
ballast has remained to be the weakest link in the system of load bearing which does not permit
any substantial improvement in addition to the stones quality (Milne et al., 2020 ). The
investigated possibilities including ballast bonding have been unsuccessful due to numerous
reasons among them an increase in the speed of travels under dynamic stress influence from
railway operation resulting in a rise in the rearrangement of the grains within the ballast bed.
Su ch results in progressive deterioration of the position of the track.
Load ablation
The superstructure defines the upper component of the whole body of the railway and is
designed to lie on the superstructure. All constructions beneath the formation protec tion layers
are a component of the superstructure. Such are among them the engineering structures as well as
the earths and drainage systems.
The key requirements of the ballast bed include:
ï‚· Ballast has to be properly compacted
ï‚· Track has to be brought into designated end position
ï‚· Ballast has to be properly consolidated
ï‚· Proper restoration must be done on the normal ballast cross -section
Machines are used in the ballast bed tamping and at the same time consolidation of the ballast in
front of sleeper end s. Lateral displacement optimal resistance is attained when the track dynamic
stabilization has occurred upon tamping and consideration of the sleeper end. Since loose ballast
may be best consolidation through horizontal vibrations, the property is applicable with dynamic
track stabilizer
The ballast bed needs to be free from organic substances for proper functionality and durability.
Still, it needs to be ab le to tolerate surface water. An integral aspect of the durability is among
the reasons for cleaning ballast (Praticò and Giunta, 2018 ). Ballast bed contamination is linked
with various effects. There is a decline in the friction between the ballast stones , a reduction in
the angle of the pressure distribution as well as a rise in the subgrade pressure. Fouling leads to a
reduction in the ballast bed elasticity and as a result continuing the track geometry durability.
The quality of each of the substances used in its construction influences the track system , and
hence the ballast material quality. Ballast is the most ideal material for bedding. Track ballast is
often broken and screened natural stone (Sayeed and Shahin, 2018 ). The following are among
the designated features of the track ballast stones:
ï‚· High toughness
ï‚· Weathering resistant
ï‚· High compressive strength
ï‚· The rocks have to break with sharp corners
ï‚· High compressive strength
The most appropriate ballast is extracted from hard rocks for instance grani te, basalt or even
diabase. Soft rocks for instance dolomite, limestone and sedimentary rocks tend to be used less
often. The ballast has to attain the required performance standards:
ï‚· A given amount of oversized or undersized stones
ï‚· Particle distribution a s well as particle size by sieve line or even sieve curve
ï‚· Shape of the grain
Track Substructure Design and Geotextiles
Geotextiles installation has been imperative to numerous track projects laid on weak foundation.
The fabric material works by enhancing the track drainage effectiveness besides maintaining a
significant dry condition for the specific ballasted profiles which in the end serve to limit the
subgrade softening (Jadidi et al., 2020 ). Still, the geotextiles outstanding performance is noted in
the railway substructure stabilization, the economic benefits as well as the simple installation
procedures which have rendered the geosynthetic among the leading alternatives for most of the
availa ble materials for drainage design . A number of principles needs to be taken into
consideration in designed filter capability including:
ï‚· The biggest pore size in geotextile has be to adequately small to retain the subsoil larger
particles hence enhancing the particle retention management. Formation of a filter bridge
occurs, as noted of the geotextile over the surface by larger particles for the purposes of
filtering the small particles seepage
ï‚· An adequate number of geotextile openings is needed for ensuring consistency in the
flow during the filter design life, mostly for reduction of the chances of clogging
ï‚· Most of the geotextile openings have to be larger in comparison with the subsoil smaller
particles thus permitting proper soil particles passages via the fabric filter. Inappropriate
design of the filter as a result of smaller sizes of the pore will lead to clogging which
would consequently lower the ability of drainage of the railway system.
Sub ballast
Sub ballast defines the gradual layer situated beneath the ballast and just above the subgrade that
has been laced either as a specific layer o even undergone evolution from the wear of the
particle, densification as well as old ballast layers settlement as a result of numerous years of
track maintenan ce and loading (Sadri and Steenbergen, 2018 ). The latter conditions tend to be
quite typical of the railway systems which have for a long time been active as well as in cases
old roadbed is serving as sub blast layer.
Sub blast serves to minimize the stre ss the subgrade is subjected to as a structural layer in the
same manner as bal last by an amount that dependent on the resilient modulus as well as the
thickness. The load bearing ability of the sub blast layer influences the stiffness and is to a great
ex tent dependent on the compacted density which is in turn influenced by the degradation.
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