Behavior of turnout sleepers in a large-scale ballast box test

Turnouts are essential components of the railway infrastructure. Their sleepers change in length leading to asymmetric loading and structural discontinuities. This accelerates ballast wear and sleeper settlement creating challenges for maintaining track geometry and safety. Understanding load transfer from sleepers to ballast is key to improve railway durability and performance. This study examines the settlement behavior of turnout sleepers and the pressure distribution beneath them in a large-scale laboratory ballast box test. Cyclic loading tests were conducted on a long concrete sleeper with and without under sleeper pads (USP) to compare their load transfer characteristics and settlement behavior. For this laser displacement sensors and pressure mapping sensors (Getzner Sensor Sleeper technology) were used. A vertical cyclic load, oscillating between 5 kN and 160 kN at frequencies of 3 Hz to 5 Hz, was applied to one side of the turnout sleeper, while a constant load of 10 kN was applied to the opposite side to represent the structural stiffness of the turnout. For each test configuration more than four million load cycles were carried out. The sleeper showed a degressive settlement pattern with asymmetric distribution. The use of USP resulted in more uniform and gradual settlement, more uniform pressure distribution and reduction of pressure peaks over time. Additionally, the sleeper deformation caused by the load was mitigated and the occurrence of voids underneath the sleeper was significantly reduced. The sleeper with elasto-plastic USP show larger initial oscillation amplitudes due to the pad's elasticity, which stabilizes over time.