A series of large scale repeated load triaxial tests on a crushed meta sandstone railway ballast is described. The effects of different gradings ondegradation and accumulation of permanent strain are investigated. The material tested was a mechanically strong ballast aggregate with grading curves similar to the envelope curves in the Norwegian railway ballast specification (EN13450, category E) and the finer grading AREMA 4, commonly usedin US on railway mainline tracks. The scope of the research was to assessthe influence of grading on ballast breakage and permanent vertical deformation. Breakage and production of fines are important for ballast servicelife, and permanent strain is affecting the duration of track alignment due to tamping. As an approach to simulate the impact from ballast tamping,each test specimen was loaded totally with 4 million load repetitions butdismantled and rebuilt after each 1mill load applications. The results ofthe study indicate that an increase in average grain size to a single-graded ballast material gives more permanent strain, more ballast breakage aswell as slightly more production of fines less than 0,063mm. The recompaction from train loads after each tamping operation is the main cause to ballast particle breakage (voids filled).
Abstract