Adelaide Hills Rail
The addition of 12d Track (for rail) to 12d Model software has helped many
designers produce better results, especially when customisations are applied.
The use of 12d Model with 12d Track on the Adelaide Hills Rail project saved
time and money, and assisted design processes greatly.
It was necessary on this project to have plotted cross sections showing rail
design formation with the track infrastructure correctly displayed. This meant
having the ballast, sleepers and rail profiles shown in all cross sections, but
on the correct cant at the horizontal curves.
It was also important to be able to calculate the exact ballast depths under
the sleepers at both (high and low) rail locations. This value was critical as
all the loads of the train were directly bearing under the rail foot, and the
minimum designed depth needed to be maintained. Axle loads in the Pilbara in
Western Australia on heavy haul rail are reaching up to 40-tonne limits.
After creating the super alignment consisting of horizontal and vertical
geometry, the Cant Panel macro (and then the Plot Rails macro) were applied.
There were 4 important inputs required in the Cant Design Tab:
(Both Kec and Ksc are constants, where item 4 in reality is variable in rail
The designer then produced a ‘speed table’ which calculated the
cant (superelevation) required to accommodate the speed and radii of design
curves. The mathematical formulae of these can vary slightly depending on the
rail size and gauge between inside rail faces.
The Kec constant is derived
from the formula Kec = S/g * (3.6)² where S is the centreline spacing of the
rails, g is gravitational acceleration (taken as 9.8m/²) and 3.6 is the
conversion factor to allow the use of V (km/h) instead of Vm (m/s).
example of heavy haul rail was using 68kg rail with 75mm width of rail head on a
standard gauge being 1435mm → 1435 + (2 * 37.5mm) / 9.8 * 3.6² which = 11.89 Kec
This 11.89 value was used in calculating the applied equilibrium cant
The formula used for that was Eе=11.89*V²/R where V is speed and R
is horizontal radius.
The item 4 value, although being a constant, did vary
pending each curve on the design. The value was brought about by the curve
requiring some deficiency in the calculated equilibrium cant. The idea of cant
deficiency being a lower cant than calculated is to ‘drive’ the train with
gravitational force into the rails, thereby having a smoother continuous ride
than any slack between the wheels and the rails where the ideal equilibrium was
originally calculated. This value is generally two thirds (~66%) of the chosen
applied cant Ea to the equilibrium cant.
Therefore, after all that to
calculate item 4, simply 66% of Kec Value, an example being 11.89 *0 .66 = 7.847
The next step in the design process was to run the Plot Rails macro.
This macro produces 12d models for rail strings, ballast string & sections and
This example had a sleeper depth of 200mm, minimum ballast depth
under sleeper of 200mm and rail with seating pad of 235mm. This equated to 635mm
above the designed rail formation. The height offset was 0.635. The other
dimension Rail to Ballast height was 0.235 (correct as the ballast came to the
top of the sleeper level when there was no sleeper present, as sleepers spaced
generally 600mm centre to centre). Also worth explaining is the width, which is
the ballast shoulder edge to shoulder, in this case 150mm is used for the
shoulder and sleeper width is 2520mm, therefore 2.82.
The simple choice of
selecting the correct Rail Type, (base of rails tab) was applied only after the
using the Rail Profiles macro.
This allowed importing previously profiled
rails into the project. The ‘examplerail.profile’ file supplied with 12d Model
was copied into the project, then the File I/O was used.
This was extruded
and displayed in a Perspective OpenGL view, but still was only a point in a
typical cross section indicating top of rail - there was no rail profile. The
designer wanted to take things a bit further with some innovative ideas.
first objective was to establish what 12d Model could already produce, and then
see if it could be enhanced further. Using the Plot Rails panel produced the
rail model strings at gauge centres (face to face), and the correct cant.
ballast required that a ‘ballast.tin’ be created from the models with the
default ‘nulling’ values; this enabled the TIN to be viewed and cut, giving the
ballast shape at any point along the alignment.
The next items were the
sleepers - this simply required a ‘corridor overlap’ in the cross section plot
routine to include the sleepers. This overlap was half the sleeper spacing, with
sleepers designed at 600mm centres then 300mm.
The rail required a symbol to
be drawn that could be called up in the cross section plot routine. Yet, it was
necessary to draw two symbols as the insertion point was on the face of the rail
because 12d Model produced strings at rail gauge centres; standard gauge being
1435mm (broad – 1600mm; narrow -1000mm).
The origin of the symbol was
critical to the correct placement on the rail model string. The rail model
strings had to be renamed to identify the left and right rails. Increasing
chainage direction to determine left and right was used. This was important when
using the plot routine.
Once the designer had all the tools to start
populating the cross section plot PPF editor, since a left and right rail
profile appearing with the correct symbol was desirable, it was necessary to
ensure a separate name within the rail string model for left and right. The
reason was that when ‘Cuts’ are used in the plot routine a defined set of
numbers is allocated and newly created rail symbols can be positioned on the
associated defined sets.
After running the plot routine, a cross section was
developed and accomplished, having plotted cross sections showing rail design
formation with the track infrastructure correctly displayed.
The final output
was exactly as desired, and further benefits flowed through. The quantity of the
ballast became easier to calculate by applying a ballast TIN to formation TIN
volume report and simply deducting sleeper cross sectional areas. Another great
advantage was that 12d Model’s Visualisation could be used to create different
rendering and realistic drive through movie (*.avi) files.
The task of
establishing the exact ballast depth below the rail foot was a matter of
applying some innovation to the data that had been created. It was necessary to
first understand why this can vary, and how to rectify the issue if the minimum
depth specified is encroached.
The area where this was likely was in
horizontal curves only - this is where the cant or superelevation occurs and
which puts the sleepers and rail on a one way cross fall. The designed formation
below is generally crowned but can also have one way cross fall, normally for
use in rail duplication projects which require drainage run off. This formation
cross fall grade is about 2% either crowned or one way. Problematically, if the
cant designed for that particular horizontal bend is greater than the formation
grade of 2%, then these two grades would eventually cross one another as the
cant being steeper than the formation. The low rail is where the ballast depth
encroachment will occur.
Once this information was gathered, the designer
could start working with the 12d Model rail left and right strings created
earlier by the Plot Rails macro. The track criteria example:
47 kg/m Rail inclusive of rail seat – 141mm
Sleeper depth under rail seat – 200mm
Ballast under sleeper at rail seat – 200mm
Fall of formation by ½ rail gauge – 717.5mm * 2% = 14mm
As mentioned, the ballast depth can be an issue when there is one-way cross fall
on the design formation and not a typically crowned formation. Some engineers
will debate that having a reduced ballast at the centre of the track is not an
issue considering the loads are somewhat reduced compared to directly over the
rail. This means a reduced value in this example by 14mm, therefore 186mm
ballast. This does contradict the design specification which dictates a minimum
of 200mm ballast under the sleeper, but the criteria generally do not indicate
where along the sleeper. So adding the 14mm ensures the minimum is maintained at
the crown work point under the sleeper and an additional 14mm (in this case)
under the rail.
The combined dimensions total 555mm - this is the input value
in the Height Offset panel described earlier. The next step was the 12d function
of draping onto a TIN. The created models of the left and right rail strings
(yellow points above sleeper) were draped onto the design formation. This
created the draped strings on the design formation. The next step was to create
a QA Report within the 12d environment. Here the ‘Check As Built Design String
vs Design String’ at 10m intervals was used (the Xfall/Offset report can also
As Built String = draped string
Design String = Top of rail string (above sleeper)
Control String = Alignment CL (shown at crown of red formation)
The results of such reporting can be exported into Excel software and, using
‘if’ statements, the designer can colour highlight ‘cells’ indicating less than
555mm. This final report can be a great resource for design considerations
between the designer, engineer and the client.
These results can show some
areas where ballast is less than desired. One must consider the depth change and
over how many meters of the alignment where this reduction is occurring and may
not warrant any work to the existing design. Yet, if there are significant
distances where the ballast is far less than desired then the designer can
increase the rail height locally in these areas of concern. This is a difficult
task. Heavy haul rail design has specific criteria for vertical intersection
points (VIPs) which is commonly a distance of 1000m between VIPs. This can cause
higher ballast volumes than necessary due to some local earthworks dipping which
dictates the low point between VIPs. The cant can also be looked at by reducing
the value thereby reducing the height variation between high and low rails,
which in turn would increase the depth between the draped string on the
formation and the new low rail position.
The other alternative is to steepen
the formation locally by introducing a new VIP and maintain the rail 1km VIPs as
this is the primary running surface of the train but the earthworks below can
vary to accommodate design constraints. Best adopt a super alignment for rail
and another for the design formation. This is common as the longitudinal plotted
profile needs to show both alignments. The combination of the existing rail
macros and 12d functions such as drape, followed by creating a report, validates
the ballast depth which ensures the client the design criteria is validated and
more importantly meant being able to calculate the exact ballast depths under
the sleepers at both (high and low) rail locations.
Despite the many difficulties involved in such a complex project, the use of 12d
Model with 12d Track on the Adelaide Hills Rail saved time and money, and
assisted design processes greatly.
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