1. The “Top Down” Approach of Diagnosing Below Rail Problems
Authors:
Mike Martin (QR), Tim McSweeney (CQU), Darryl Nissen (QR)
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2. Two basic steps involved:
Introduction
A common limitation of railway maintenance practice is the lack of a proper investigation to diagnose the cause of the problem before attempting a solution.
Two basic steps involved:
1. Proper investigation of degraded track geometry by trained personnel;
2. Appropriate testing procedures to determine the root cause of the problem.
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3. Primary Objective
To minimize the need for reconstruction by not allowing chronic problems to develop or go unrecognised/untreated.
(To this could be added that we shouldn’t continue short term solutions when a long term ‘fix’ is the only economic solution)
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4. The “Top Down” approach In simplistic terms, this process involves:
Data collection/Desktop review
Field Inspection
Sampling/Testing (if req’d).
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5. Step 1: Data Collection/Desktop Review
Gross Tonnages/Speeds/Axle loads
Sleeper type and spacing/Rail Size
Capping layer present (?)
Previous history (eg what was sleeper type or rail size previously; what tonnages has the track carried)
What is the intended future usage in terms of traffic task, axle loads, tonnages, predicted life, etc?
Resurfacing frequency
Track Recording Car data
Track Condition Index
Rainfall data (especially recent events)
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6. Step2: Field Inspection (Essence of the “Top Down” approach)
Inspect (in order) the following:
Rails
Sleepers
Fastenings
Ballast
Capping
Subgrade
Drainage
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7. Glued Insulated Joints? Poor Welds? Incorrectly stressed rail?
Example 1: Rail
Corrugations present?
Wheel Burns?
Squat Defects?
Poor Joints?
Glued Insulated Joints?
Poor Welds?
Incorrectly stressed rail?
Pull aparts?
Buckles?
Are there splash marks on the web of the rail
indicating that ‘pumping’ has been occurring?
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8. Degraded (timber) sleepers present?
Example 2 : Sleepers
Degraded (timber) sleepers present?
Damaged (concrete) sleepers present?
Is sleeper spacing uniform?
Are sleepers straight or at an angle?
Is there pumping at the joints?
(Often occurs for interspersed steel sleepers)
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9. Ballast depth: is it sufficient for task?
Example 3. Ballast
Ballast depth: is it sufficient for task?
Has ballast deteriorated/broken down? (Often smaller sized ballast in the crib area compared to the shoulder area)
Is there evidence of moderate or severe fouling? (Coal fines?)
Are there ‘mudholes’/’pumping’ of sleepers present that may have resulted from ballast having lost its ability to drain water ?
Does the ballast exhibit ‘rolling’ or discolouring to a dirty grey colour indicating the onset of ‘pumping’?
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10. Step 3: Field Sampling/Testing
(Note that this step may only be necessary if the revious steps have failed to accurately identify the problem)
Sampling of capping and/or formation to determine grading and plasticity (Atterbergs)
Dynamic Cone Penetrometers (DCP’s) to determine subgrade strength
Trenching to determine layer depths/presence of ballast pockets/presence of moisture
GPR of long track lengths to determine ballast depths
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