1. Steve Barlow Pandrol Asia-Pacific
Development of a simple prediction model for slab track vibration using field measurements
Steve Barlow
Pandrol Asia-Pacific

2. Scope of study Consider only concrete slab track.
Consider only vibration, not noise.
Consider only the vibration measured on slab adjacent to rail fastener.
Do not consider vibration transmission through or from structure
Hence, only concerned with the performance of the fastener itself.

3. PART 1
What is Slab Track?

4. Cast-in baseplates

5. Pre-cast block track

6. Embedded sleeper (1)

7. Embedded sleeper (1)

8. Embedded sleeper (2)

9. Embedded sleeper (2)

10. Plinth track

11. RHEDA track

12. J-slab

13. Precast FST slab track

14. Embedded Rail

15. What are we trying to achieve with slab track?
Reduce the space taken by trackform, particularly in tunnels
Reduce maintenance liabilities
Keep costs down
Reduce the track stiffness

16. Low stiffness rail fasteners
PART 2
Low stiffness rail fasteners

17. Reducing track stiffness – why?
Want to reduce ground borne vibration (a.k.a.structural noise)
Theory tells us to either:
1. Increase mass (e.g. FST)
2. Reduce track stiffness

18. Options for lowering slab track stiffness

19. Conventional baseplate
Rail foot fastened by steel spring clips
Vertical stiffness limited by rail roll (typically 15 to 20kN/mm static)
Typically 2.5mm maximum vertical deflection

20. Conventional resilient baseplate with spring clips

21. Low stiffness baseplate
Supports and clamps rail by the web
Low vertical stiffness (typically 3 to 5kN/mm static)
Vertical rail deflection up to 6mm typical
Straight swap for existing baseplate in most cases

22. Low stiffness baseplate clamping rail by the web

23. Description of field measurement locations
PART 3
Description of field measurement locations

24. Location 1 Hong Kong MTRC Plain slab at grade Installed January 2002
Straight swap for existing soft fasteners
7.4dB insertion loss measured on slab

25. Location 2 Hong Kong Airport Railway Viaduct on 300 metre radius curve
Fitted January 2004
Retrofit to replace existing ‘soft’ baseplate
8.2dB insertion loss and 5dB(A) less secondary noise beneath viaduct

26. Location 3 London Underground – Victoria Line
Retrofit to slab track Cast-in sleeper version
Operational since March 2000
Gives 16.2 dB insertion loss on slab
More than 125MGT traffic since operations began

27. Location 4 Madrid Metro Line 11 Installed August 2001
Replacement of existing stiff fastener on booted block
23.1dB insertion loss recorded on slab

28. Location 5 Guangzhou Metro China, Line 1 Installed 2005
345m radius curve and tangent
Retrofit for stiff fastener
11.5dB insertion loss on slab

29. Swapping over baseplates
PART 4
Swapping over baseplates

30. Swapping over baseplates
Raise rail temporarily
Remove old baseplate
Use other rail as datum
Position new baseplate

31. Swapping over baseplates
Low stiffness baseplates positioned
Clamping tool used to fasten rail
Once alignment is set, start work on other rail

32. Swapping over baseplates
Both rails clamped and aligned
Take ‘after’ vibration recordings immediately

33. Taking vibration readings
PART 5
Taking vibration readings

34. Measuring vibration Multiple train passes for each case
Train speed constant
Time lapse between before and after measurements minimised
Same recording and reporting method used in all cases

35. Taking slab vibration readings
Accelerometers screwed to steel plates, bonded to slab
Positioned close to rail foot at mid-span where possible
Data recorded and processed in the same way every time

36. Factors affecting vibration results
Rail condition and geometry
Wheel condition
Train speed
Local conditions
Track structure

37. PART 6
Vibration results

43. Change in static stiffness of rail fastener
Units
Location reference 1 2 3 4 5
Static secant stiffness before (Ks1)
kN/mm 21
133
130
52.1
Static secant stiffness after (Ks2)
5.1
Stiffness change (Ks1/Ks2)
5.25
26.1
32.5
13.0
Insertion loss (total vibration)
(dB)
7.4
8.2
16.2
23.1
11.5

45. ~15dB insertion loss change per tenfold static stiffness change

46. Steve Barlow Pandrol Asia-Pacific scb@pandrolasia.com
END
Steve Barlow
Pandrol Asia-Pacific