Degradation of railway ballast through large scale triaxial and full scale rail track model tests

Comparison with mechanical laboratory tests

Abstract

The aim of the research was to assess if the standard tests provided a reliable ranking of nine ballast aggregate materials with respect to mechanical strength. Standard tests were compared with the results from large scale triaxial and full scale model tests employed to simulate in-service stress and environment. Four different mechanical strength tests were conducted on nine crushed rock railway ballast types with fixed grading (22.4 - 63 mm) to investigate degradation with respect to breakage and production of fines. The equipment used are the standard tests: Los Angeles Abrasion (31.5-50 mm/10-14 mm) and micro-Deval (31.5-50 mm), large scale repeated load triaxial, and a full scale railway track model test for cyclic loading, all performed in the laboratory environment. The test procedure also included simulation of the impact loading from tamping. Aggregate petrographic tests were used to reveal whether there was any possible rating weakness associated with the mechanical strength. The rock samples were three igneous rocks, four metamorphic rocks and two consolidated/ metamorphosed sedimentary rocks, all fine and medium grained. The results of the study indicate that the three types of mechanical tests rank the ballast samples in three different ways.