Performance enhancement of railtrack ballast with rubber inclusions: a laboratory simulation

Abstract

Railway ballast, which form an integral part of railtracks, is highly susceptible to subsistence due to both vibration transmitted by the passing trains, as well as the breakage of the ballasts themselves with repeated impact. The resulting subsistence necessitates regular monitoring and maintenance, involving cost- and time-consuming remedial actions, such as stone-blowing and ballast renewal. It would therefore be desirable if measures could be taken to minimize the wear and tear effect of the rail traffic, consequently to prolong the lifespan of the ballast layer. This paper describes the exploratory work on rubber inclusions to address this problem. The rubber elements were derived from the inner tubes of motorcycle tyres, cut and shaped accordingly to produce various configurations for the study. Granitic stones of suitable size were sieved and used as representative samples of typical ballast as the tests were mainly carried out with a standard direct shear test setup, i.e. shearbox measuring 60 mm x 60 mm. The rubber tubes were cut and shredded to produce strips and shreds respectively, and the elements were arranged in various pre-determined configurations within the simulated ballast layer. The direct shear test results indicated that rubber inclusion could effectively improve the shear resistance of ballast to various degrees, though the configurations clearly played an important role in the improvement observed. Both strips and shreds were found expedient in deformation control with increased ductility of the composites, with potential to absorb impact and reduce breakages of the ballasts. Both mechanisms contributed to the reduced overall subsistence, accompanied by an increase in the shear resistance. As such, the present study indicates a promising application of the material in improving the performance and longevity of existing ballast layer in railtracks. Nonetheless, considering that the test setup is but a static, scaled down simulation, without dynamic loading which mimics the rail traffic, it is necessary to conduct further investigations in instrumented full-scale setups for verifications prior to filed implementation