Keywords: railway, turnouts, rail measurement, vertical displacement, ballasted track, wayside monitoring.

Turnouts are critical units in railway systems, as they perform the switching procedure that guides trains along different routes. Obtaining measurements of the dynamic behaviour of turnouts under different load conditions helps to improve their design and develop better maintenance strategies. This paper presents two wayside monitoring methods for measuring low frequency vertical displacements of rails affected by train passage; it tests these methods in a case study of the Iron ore line (Malmbanan) in northern Sweden. Rail displacements were measured with two wayside monitoring systems, not the more common inertia system on a track recording car used by the Swedish infrastructure maintenance contractors. The first wayside monitoring method used a laser based sensor to measure the displacements of the rail relative to a measurement rig. It also had a second laser based displacement sensor and an accelerometer to detect any movement of the measurement rig. The second wayside monitoring method, a water pillar system, measured track displacements by measuring the water level of a pipe mounted on the track connected to a cistern placed outside the embankment. This system created a reference position outside the embankment of the turnout, unaffected by passing trains. From the measurements, the rail displacement could be determined for a passing passenger train; viscoelastic behaviour of the track could also be detected, which cannot be done using a regular track recording car.

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