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Measuring the Contact Area and Pressure between the Ballast and the Sleeper Taufan Abadi

Measuring the Contact Area and Pressure between the Ballast and the Sleeper Taufan Abadi Dr. Louis Le Pen Dr. Antonis Zervos Prof. William Powrie. Aims/Objectives:

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Measuring the Contact Area and Pressure between the Ballast and the Sleeper Taufan Abadi

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  1. Measuring the Contact Area and Pressure between the Ballast and the Sleeper Taufan Abadi Dr. Louis Le Pen Dr.Antonis Zervos Prof. William Powrie

  2. Aims/Objectives: • To explore the potential of pressure paper to give reliable contact information at the sleeper/ballast and ballast/subgrade interfaces. • To use pressure sensitive paper to evaluate how ballast gradation, sleeper type and under sleeper pads influence the contact behaviour at the sleeper/ballast and ballast/subgrade interfaces. Material & Method: Pressure Paper A pressure sensitive thin film is used which is available in different pressure sensitivity ranges. The paper turns red with the intensity of the red colour and this can be used to measure the maximum pressure applied. In this work the ranges used were 0.5-2.5MPa, 2.5-10MPa, and 10-50MPa.

  3. Ballast To assess whether a more well-graded material would distribute load more uniformly three non-standard gradations of ballast (granite) including larger proportions of finer material were tested. Increasing finer proportion

  4. Apparatus The Southampton Railway Track Facility (SRTF) comprises two vertical sides 5 m long and 0.65 m high, constructed from heavy steel sections and panels, held at a fixed 0.65 m apart, maintained as close to plane strain as practicable. Plan view of the SRTF

  5. The SRTF and Location of Pressure Paper Sleeper soffit Ballast/rubber mat interface

  6. Detail of the Tests • General test conditions: • Tests were carried out with the vertical load cycled at 3Hz for 3 million equivalent 20 tonne axle passes. The ballast was placed to 300 mm depth and typical size ballast shoulders and crib ballast were placed. • Mono-blocksleepers, 7 tests were carried out covering: • 1 baseline test on Network rail gradation ballast • 4 tests on ballast gradations with increasing finer proportions • 2 tests on Network Rail gradation ballast with two different types of under sleeper pad (hard, soft) • Twin-block(twin block) sleepers, 4 tests were carried out covering: • 2 baseline test on Network rail gradation ballast • 1 tests with a hard under sleeper pad • 1 tests with a soft under sleeper pad

  7. Results: SLEEPER/BALLAST interface with GRADATION Baseline test Increasing finer proportion

  8. Results: SLEEPER/BALLAST interface with USPs MONOBLOCK Baseline test Hard USP Soft USP DUOBLOCK Hard USP Soft USP

  9. Results: Number of contacts • Large variability in data, however some trends can be observed: • Careful changes to ballast gradation can increase the number of contacts • The use of USPs does not appear to increase the number of contacts

  10. Results: Percentage of sleeper base in contact Observations for the 10-50MPa range pressure paper: At sleeper/ballast interface, it is not always that more contacts create a larger contact area. Twin block has smaller sleeper soffit areaand has less contacts compared to mono-block. Modifying the sleeper/ballast interface by introducing finer material can increase the contact area by up to 3x. USPs increase the area of contact significantly (4.5 to 29 times for twin-block and 4 to 7 times for mono-block.

  11. Result: BALLAST/SUBGRADE >10MPa Mono-block sleeper baseline Mono-block sleeper Finest gradation Mono-block sleeper SOFT USP Twin-block sleeper baseline Twin-block sleeper SOFT USP Table of results on next slide…

  12. Result: BALLAST/SUBGRADE >10MPa In general, contact patches under the railseats are larger than beneath the sleeper middle. The USPs and the introduction of finer material help to spread the load to a larger area of the subgrade.

  13. Red Intensity Calibration

  14. Result: Contact Pressure ballast/subgrade >10MPa • Observations: • Standard ballast transferred very high pressures to the subgrade. • USPs did not significantly alter the maximum pressures on the subgrade. • Some of the finer gradations show reduced maximum subgrade pressures. • However considering only the maximum may not be the best indicator – further work

  15. Conclusions: • Pressure paper is able to record the number of contact points between the ballast and the sleeper soffit, and the percentage of the total area in contact between the ballast and the sleeper soffit and the ballast and the (softer) sub-grade, as aggregated values over a loading history. • For G44 mono-block sleepers, a range of ballast gradations showed between 147 and 836 contacts over 7 tests covering loading histories of 1.0 to 5.0 M cycles of 20 tonne equivalent axles loads. • For a duo-block the number of contacts was between 164 and 268 contacts over 4 tests covering loading histories of 0.25 M and 6 M cycles of 20 tonne equivalent axles loads. • The introduction of the right sizes and portion of finer particles has the ability of increasing the number and the area of contact at sleeper/ballast interface. • The installation of under sleeper pads increased the area of contact and reduced the maximum pressures.

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