Study on ballast particle movement at different locations beneath crosstie using "smartrock"

Ballast compaction and particle rearrangement cause ballast to rotate and move vertically and horizontally. Ballast movement, including translation and rotation, has a significant effect on track performance. Large movement of ballast particles leads to track geometry roughness, e.g., hanging ties, and thus increases potential of damage and deterioration to rails, ties and fastening components. This study investigated ballast particle movement at different locations beneath a crosstie. In the paper, a wireless device - "SmartRock" was utilized to monitor ballast movement under cyclic loading in laboratory tests. The SmartRock has a shape of a realistic ballast particle. Inside the SmartRock was imbedded a tri-axial accelerometer, tri-axial gyroscope, and tri-axial magnetometer with 9 degrees of freedom so that particle translation, rotation and orientation can be interpreted, relatively. The real-time measurements were recorded by the SmartRock and then sent to a computer via Bluetooth. In the laboratory tests, a ballast box was constructed. In the ballast box, a half section of a typical railroad track was constructed. Five hundred cyclic load repetitions were applied on the top of the rail. Translational and rotational accelerations of the particle were recorded by the "SmartRock". Three ballast box tests were conducted. Two SmartRocks were placed beneath the middle of tie and the edge of tie, respectively but at different depths during each test - right under the tie, 12 cm beneath the tie and 25 cm beneath the tie. The results indicated that (1) ballast particles had translational as well as rotational modes under cyclic loading; (2) ballast particles had rotation together with horizontal translation; (3) particle rotation were higher beneath the edge of tie than those beneath the middle of tie; (4) Ballast movement were significantly reduced with depth. The paper also further confirmed that the SmartRock was capable of recording real-time translational and rotational accelerations, which would not have altered the motions of surrounding ballast particles due to its realistic shape of a particle, hence, provided a new means to monitor ballast particle movement in railroad engineering.