The phenomenon of track deterioration is thought to be significantly affected by the pressure on a sleeper bottom and ballast vibrating acceleration. However, these physical quantities have not yet been measured with high precision. The RTRI therefore developed a sensing sleeper with a number of thin impact force sensors attached to the whole undersurface of the sleeper (Fig. 1). The RTRI also developed a sensing stone with two built-in triaxial acceleration sensors to measure the movement of crushed stones in any direction (Fig. 2). The sensing sleeper is used to evaluate improvement of the conditions of contact between sleepers and ballast stones, while the sensing stone helps to evaluate the reduction of maintenance costs of ballasted track.

The RTRI expresses numerically the three-dimensional shape of a ballast stone as a polyhedron model, and compacted more than 28,000 polyhedrons, each modeling a ballast stone, to represent a whole full-scale ballasted track structure with a three-dimensional distinct element model. By inputting the load waveforms as measured upon train running on an actual track into this model, the RTRI numerically reproduced the dynamic behavior of both the sleepers and an assemblage of the ballast stones through simulation. The analytical results were compared with the values as measured using the sensing sleeper and the sensing stone on an actual track, and it was confirmed that agreement roughly holds in the time-dependent displacement characteristics of sleepers between analysis and measurement (Fig. 3).