Role of particle breakage on damping, resiliency and service life of geogrid-reinforced ballasted tracks

Abstract

A series of cyclic loading tests were performed to establish the effect of particle breakage on the damping, resiliency and serviceability of railroad ballast. Five geogrids of triangular, square and rectangular apertures with different sizes were used to stabilize the ballast having the mean diameter (D50) of 42 mm. It was established that the particle breakage that occurs during cyclic loading helps in energy dissipation and also enhances the track resiliency. Further, the quantum of particle breakage is governed by the extent of lateral and vertical strains in ballast. Accordingly, empirical relationship has been established between breakage reduction index, BRI with the lateral and vertical spread reduction indices, LSRI and VSRI. The damping ratio (Dr) and resilient modulus (Mr) is shown to increase with the increase in particle breakage (Bg). Furthermore, the volumetric (εvol) and shear strains (εs) in ballast at the end of testing was found to be influenced by the particle breakage (Bg). Further, the track life enhancement factor (Lef), defined as the ratio of number of load cycles (N) required to attain a given extent of strains in ballast in case of geogrid-reinforced ballast (Grb) to that of unreinforced ballast (Urb), is found to vary from 500 to 1 for 0.3 and 0.5 % lateral strain and 12.50 to 1 for 2 and 3 % vertical strain. The Lef was found to be highest in case of geogrid G1. In addition, a unique relationship is established between Bg and Lef wherein it was found that as the particle breakage increases, the service life of track reduces.