Keywords: deflectometer testing, trackbed, ballast, speed limits, critical velocity, stiffness, NDT, track deterioration, heavy haul, asset management, whole life costs.

New railway lines are constructed with stiffness in mind, but this was not the case 100-150 years ago, when most national networks were established. The trackbed on many of these routes is unsuitable for heavier axle loads and/or higher speeds experienced today. Falling weight deflectometer (FWD) is the only established non-destructive technique for practicable measurement of stiffness characteristics of a trackbed, including its critical velocity. Until recently it has only been used to evaluate the condition of known problem sites, typically characterised by either very poor track geometry or critical velocity related problems. However in the past year the FWD has been used extensively on two major route upgrades: the Midland Main Line in the UK; and the Lac La Biche Sub, a little used freight route in Alberta, Canada. The paper describes both investigations and explains how the stiffness requirements derived for UK traffic have been applied to the heavy haul tracks of North America.

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