NEW TRACKBED assessment techniques devised by consultants are saving contractors money by eliminating unnecessary maintenance and renewals work, a meeting of the Railway Civil Engineers Association heard this week.
Consultant Scott Wilson's new Total Route Evaluation technique gives a far more accurate picture of track sub layers than traditional investigation techniques, the meeting heard, which is proven to locate and solve problems with the track bed and, consequently, save money.
Scott Wilson railway geotechnics specialist Dr Philip Sharpe explained that stiffness is the key to track bed quality, but traditional investigation techniques such as trial pitting do not provide a particularly effective method of testing existing track.
Sharpe claimed that trial pits are labour intensive, awkward and dangerous next to live lines, and only provide intermittent information.
Scott Wilson's Total Route Evaluation uses a falling rate deflectometer test - a technique borrowed from road surveying - to assess the vital track stiffness.
The test works by dropping a weight on individual sleepers.
Geophones measure the deflection of the track bed at different distances from the impact, allowing the formation stiffness and critical velocity to be calculated.
The test is used in conjunction with a ground probing radar survey to show the thickness and variability of the track bed strata, and an automatic ballast sampler to take undisturbed insitu samples for detailed analysis in the laboratory.
The data gleaned from these tests can then lead to improved transition slab design, can show what effect track bed reinforcement can have, and can help calculate line speed.