Radan kokonaisjäykkyyden mittaaminen ja modifiointi

This study deals with total track stiffness measurement and modification. The main focus are the properties and measurement results of the ‘Stiffmaster’ rolling track stiffness measurement vehicle developed as part of this project and modification of track stiffness. An interim report titled ’Vertical track stiffness and measurement techniques’ on the project was published
earlier in the Research Reports of the Finnish Transport Agency 6/2013.

The load-carrying capacity of a railway track is affected by many factors, but total track stiffness is one of the most obvious indicators of it. A new rolling stiffness measurement vehicle named ‘Stiffmaster’ was developed to measure load-carrying capacity. The vehicle is coupled to a track maintenance locomotive to make continuous rail deflection measurements as it is
pulled over the track. The vehicle measures both loaded and unloaded vertical track geometry, and deflection is determined as the difference between these two values measured during the same run. The loading consists of one axle of a Tka7 railway truck that weighs 140 kN. Three light axles are used as measurement references.

Based on the measurement results, track type affects the magnitude of deflection the most. Deflection of wooden-sleepered tracks is considerably greater than that of concrete-sleepered tracks. Moreover, the thin structural layers of low volume tracks increase deflection caused by subsoil. Many discontinuities, such as fish-plate joints and bridge approaches, can often be
discerned from measurement results. On the other hand, on the main lines, where the structural layers are thicker, soft soil deposits do not stand out clearly in measurements, but shallow rock cuttings may show. Deflection varies also on the main lines, but it is usually caused by individual points of discontinuity. Sudden stiffness variations result in hanging sleepers that
can be found, for example, at bridge approaches and at the points where frost insulation slabs start. Weak sleeper support and geometric problems are most likely caused by a change in track stiffness that increases the dynamic loading from rolling stock. That is a self-accelerating problem.

Several methods of track stiffness modification are described in the latter part of the report. Structural components are analysed individually and evaluations of the effects of modifications are presented. Evaluations are based on a literature review, measurement results, and simple hand calculations. The clearly best method to increase track stiffness is to add new structural
layers to the substructure of low volume tracks. They reduce the loading on weak subsoil which decreases deflection. Replacing fish-plate jointed rails by continuously welded rails decreases variation in track stiffness significantly. On the main lines, the focus of modification should be on stiffness transition zones such as bridge approaches. The literature review revealed that composite materials can be used successfully to reduce deformations and maintenance need. Under sleeper pads (USP) have also been used to reduce stiffness variation. They can also be used to reduce noise and vibration in rock cuttings and tunnels.