Moana design approach and solutions
Where to start ?
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From a designer’s perspective, with every new project there is a request initiated
by a client(KR in this case), which comes with information of what the goal,
expectations and outcomes of the project’s design needs to be.
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Following conversations, the scope of the project needs to be clearly defined as
that is our basis for providing the design and deliverables.
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*scope creep(changes to original scope) can occur, and these can have an impact
on the design and consequently delivery times.
Reaching an agreement on the project’s objectives
List of requirements:
Specifications,
informations, purpose the
project must deliver
Request initiated by
Client
Moana – stage 1 scope:
• Replacement of the existing 91lb rail track with 50kg rail track,
Define
scope
• Replacement of TRP sleepers with concrete sleepers,
• Future replacement of turnouts 402 and 419 with new Martinus 1:9 concrete
turnouts,
• Provide the design of the track realignment for the Mainline and Loop track
sections where the rail is to be replaced,
• Assess and calculate the curve parameters for a design speed of 80km/h
DESIGN PROCESS
(work)
1
Site pictures, overview and localisation
The section of track that is to be
realigned is located around Moana
train station between km 173+730 to
km 174+540 on the Midland Line in the
South Island.
View of existing
pedestrian bridge
from the rail level.
View from the
existing pedestrian
bridge towards
Moana train station
and platform.
2
Planning the design work based on project scope
Each item in the project’s scope has a design requirement that needs to be fulfilled in order to have a compliant design
Item 1 in the project scope:
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Replacement of the existing 91lb rail track with 50kg rail
track.
This item doesn’t affect the track design too much, although
there is a slight height difference between the 50kg and 91lb
rail profiles. That difference will be considered when
developing the vertical design of the track alignment.
Item 2 in the project scope:
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Replacement of the existing TRP sleepers with concrete sleepers.
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This item is critical to the track design, there is a significant height
difference between the TRP sleepers and concrete sleepers. That
difference needs be considered when developing the vertical design of the
track alignment.
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The dimensions for TRP sleepers are 150 x 200 x 2100 (150mm height),
and the concrete sleepers are 195 x 254 x 2134 (195mm height)
How does this change affect the design?
3
Planning the design work based on project scope
Items 3,4,5 in the project scope:
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These items impact the geometric design directly, as the requirements are stipulated in KR track standard T-ST-DE-5200 and T-ST-DE5212(clearance standard)
Item 3 in the project scope:
• Future replacement of turnouts 402 and 419 with new Martinus 1:9 concrete turnouts,
• The turnouts at each end of the station extents, will be replaced in the future. This provided an opportunity to
future proof the track design while still fulfilling the requirements for the rail and sleeper replacement.
• What does a turnout replacement entail ?
Item 4,5 in the project scope:
• Provide the design of the track realignment for the Mainline and Loop track sections where the rail is to be replaced. Design speed for the curve inside the station extents is 80km/h
• In order to provide a compliant design in horizontal, vertical and in cross-section, the geometric elements need to be compliant with KR track standards, clearance standards, and
other civil/rail standards(e.g. formation, drainage, etc..)
• The design speed for the Main Line inside the station limits is set to 80km/h, as part of the scope.
• What sort of requirements does the design have to meet in order to have a compliant horizontal and vertical alignment ?
• What is the design speed for the Loop track ?
4
Developing a design philosophy based on initial requirements identified
List of requirements identified:
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Design speed 80km/h for MainLine and 30 km/h for Loop Line
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Compliant geometric design to fulfill the requirements stipulated in KR track standard T-ST-DE-5200 and T-ST-DE-5212(clearance standard). Clearances to existing structures to be assessed
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Maintain track and turnouts in their existing locations
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Lift the track to account for the change in sleepers and rail profile height
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“The design follows a “best fit alignment” approach (like for like replacement). Furthermore, the design intent is to minimise lateral movement of the new alignment relative to the existing one
(minimal slews to be achieved across the length of the section of track realigned). In this regard, minor adjustments to existing curve geometry might occur.
•
The new vertical profile has been designed to account for the change of sleepers and rail type, thus the design intends to achieve a general lift of minimum 50mm across the entire length. Minor local
adjustments will be made if this general lift cannot be achieved.
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Future proof design of the turnouts will be provided. The future Martinus 1in9 turnouts have designed and placed on constant grades, for an easier installment and future maintenance.
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Around the station platform and pedestrian bridge, the existing levels of the Main and Loop tracks will be kept as best as possible, with minor lowering adjustments to the track preferred to minor
lifts.”
5
Assessing and processing initial information received: survey, curve geometry(regression analysis), existing low rail level, etc.
Survey assessment:
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Identify existing structures(bridges), signals, station platform edge, canopy, other track side furniture. This is needed for clearance checks.
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Identify track strings and check if every critical point was picked up during survey(POS, POF,EOT) and if additional information(points) is needed. Identify existing drainage and other subsurface
utilities networks if needed, for tie-in points, diversions, etc..
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Pictures would be useful to have with the received survey, or a site inspection to better understand the existing terrain and surroundings.
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Km marks are also important to be picked up in the survey as, this is needed to set the chainage at the correct value. If they are not present on site, an approximation would need to be done.
Important observation:
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The coordinate system for the survey needs to be provided by the surveying company.
Overlaying all survey files should coincide, if one reference is out of place, usually it’s a human error and it was dragged out of place.
As an engineering designer, we rely on initial survey, but have no or little control of it. It is important therefore to have the original copy in
case of mismatches at construction phase which could lead to delays. Always keep a record!
6
Assessing and processing initial information received: survey, curve geometry(regression analysis), existing low rail level, etc.
Regression analysis:
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To perform a regression analysis on the surveyed rail tracks, means to find the best fit horizontal and vertical elements that fall within the path of an
existing track. To put it more simply, finding the middle tangent element or curve between the two rail strings.
This is a critical step in the design process, as the horizontal alignment can’t move too much, as it can have an adverse effect on clearances, ballast
shoulder widths, formation depth tolerances, etc., but you still need to comply with KR standards and provide the minimum requirements for the
geometric elements.
Observations:
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The regression analysis process uses a tool that shouldn’t be considered gospel, the alignment design needs your best judgement in order to be developed and adhere to the philosophy and
intent you’ve set.
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It is an iterative process and needs to be tailored to the existing surroundings and constraints.
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Horizontal slews can vary, with maximum values of up to 120mm.
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In order to design out imperfect geometries(multiple compound curves), horizontal slews can be increased to 200+mm, but that is only after an agreement with the regional team.
7
Assessing and processing initial information received: survey, curve geometry(regression analysis), existing low rail level, etc.
Existing low rail:
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When designing the vertical profile of the track you need to consider the existing levels you set the height to.
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The track survey you’ve been provided with, should have elevations on both rail strings on opposing sides(left and right). You will have to perform an analysis to determine which is
the LowRail elevation level.
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Why is it important?
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Not setting the correct existing levels for your track centreline vertical design, can increase the thickness of the ballast underneath the sleeper, especially on curves where you have
cant. Can also lead to substandard vertical clearances, especially under bridges.
Observations:
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Because you are using the Lowrail levels to set your new vertical design, the pivot method you need to use for your CANT calculations, is “low side rail” pivot method.
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There are circumstances where a lowrail level is not needed, usually this happens in Rail Yards, where there is no cant on the existing curves, therefore there shouldn’t be a rail
that is lower than the other. It is good practice to still perform the analysis, as undulations in the track can lead to one side of the track to be lower than the other.
Other useful initial information:
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KR curve list and corridor log – can be used to better understand existing parameters
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In this case a useful information was that the train station building is part of the Rail heritage Trust of New Zealand and represents a high historical and architectural significance to the region and rail network.
8
Assessing existing alignment based on the information received
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Before commencing the realignment detail design, we must first assess the existing conditions of the track alignment against clearances to the structures, station platform, track
spacing between Mainline and Loop track, etc..
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Why is it important?
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If existing conditions show substandard values, we have an opportunity to address these issues, or if it’s not possible we have an obligation to flag the issues, report them, and
agree on a solution moving forward that is accepted by all stakeholders involved.
Following an assessment of the Existing Moana infrastructure we found a few issues:
1.
Substandard cant gradients for the existing curve inside the station extents. Existing cant gradients are 1:400, which is below the maximum allowable CG of 1:500.
2.
Track spacing between Mainline and Loop line is at places less than 3.80m, especially on the curves, where you must take into consideration centre throws and end throws for the rolling stock.
3.
Substandard horizontal offset between the track centreline and the station platform edge. Existing offset varies, but it is below 1.45m, between 1.39m and 1.43m
4.
Substandard vertical clearance between the existing rail level and the station platform edge. Existing vertical offset varies between 260mm to 330mm, below required 530mm in the standard.
5.
Substandard vertical clearance between existing rail levels on the Mainline and Loop line, under the existing pedestrian bridge, Bridge 85. Existing values are shown in the picture below, below required standard.
9
Combine provided information and initial data to develop the new track alignment
Mainline track horizontal realignment:
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Design speed 80km/h for passenger trains and 60km/h
for freight trains
New track alignment follows existing with minimal slews
The new alignment has been slightly shifted around the
station platform to provide a minimum clearance of
1.45m.
Curve geometry has been adjusted to have the in and
out TL=45m, and a cant of 50mm, which improved the
cant gradient to 1:900.
Turnouts have been placed on straight tracks and
constant gradients for easier maintenance and a longer
design life.
Mainline track vertical realignment:
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Tie-in points at each end, match existing levels.
General lift of 50mm to allow for the change in rail profile
and sleepers
Existing levels around the station platform have been
maintained, not to deviate from the existing substandard
values and increase them(worsen the situation)
Existing levels were maintained under the pedestrian
bridge for the same reasons as above
Past the pedestrian bridge, the alignment achieves a
general lift of 40mm, until the end of the project extents
10
Clearance checks, potential departures from standard needed
Having the new track alignment, clearance checks were performed against KR standard T-ST-DE-5212, to see if any risks or safety concerns were eliminated, mitigated, or
accepted.
Issues and risks that were eliminated or mitigated with the new track design:
1. Station platform clearance, 1.45m clearance to the station platform lip was provided with the new design.
2. Curve parameters were adjusted so that a compliant geometry was provided.
3. Turnouts were placed on constant gradients for a longer design life and easier maintenance.
4. The design allowed for the formation depth tolerances to be maintained for most of the alignment, apart from the areas around the station
platform and pedestrian bridge
New Curve
parameters
11
Clearance checks, potential departures from standard needed
Other clearance checks performed:
1. Clearance check to the station canopy.
Clearance to
Canopy
Some issue were not able to be designed out,
those included:
2. Track spacing check
1. Vertical clearance to the station platform.
3. Vertical clearance around Pedestrian
Bridge 85 and the station platform (this
clearances remained the same as existing)
2. Vertical clearance to the pedestrian bridge.
3.Track spacing clearance, especially on the
curves within the station extents..
Track spacing
clearance
12
Clearance checks, potential departures from standard needed
Potential departures from standard needed:
1. Vertical offset from top of rail to top of platform lip.
See picture KR standard requirements.
2. Vertical Track clearances in the mainline and siding
track corridors around the pedestrian bridge
3.Track spacing clearance, especially on the curves
within the station extents, insufficient track spacing.
Platform
clearance
Track spacing
clearance
Structure Gauge
clearance
13
Risk and safety register
Within the project scope, a key area is the health and safety outcome of the new track design. Some aspects that present a risk, safety or
health concern can not be eliminated or mitigated through a geometric design. Other aspects refer to the lifetime operation of the asset
and regular maintenance. To try and accommodate all of these potential hazards and risks, a Safety in Design register is provided, where
an engineer foresees potential issues that could affect a person’s health, an assets failure or a major accident.
14
Summary
The approach to designing this section of track was staged as below:
1. Initial request prompted by the client to upgrade this section of track.
2. Understanding the client’s requirements and expectations and defining a scope for the project.
3. Assess and understand initial information received from the client (survey, curve list, other data..)
4. Develop a design philosophy as a guide for your approach and intent for the realignment of the track.
5. Assess existing track alignment conditions and constraints.
6. Develop a new track alignment taking into consideration all the data received and assessed previously.
7. Perform clearance checks and safety assessments(risk assessments), to reach a consensus and a agree on a solution
or compromise
8. Develop final deliverables and documentation for review and sign-off.
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Questions ?
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