ABSTRACT

The aim of the study was to predict the service life of railway ballast based on information from the rock’s mechanical strength represented by Los Angeles value and micro-Deval value. The study assesses the influence from train traffic, ballast tamping and type of rock. Train traffic was simulated by using cyclic loading and a full scale rail track laboratory model (test box). The ballast was cyclic loaded 4 million times and tamping was simulated by interrupting the loading process after every 1 million loadings by loosening the ballast compaction. The axial load was 25 tons and totally 9 different rocks were investigated, most of them not weathered.

Tamping is essential regarding degradation and is indirectly the main contributor to the crushing process through repeated ballast loosening and compaction. The train traffic beyond the first 10 000 axle passages is of minor importance regarding crushing. If the ballast’s mechanical strength can be improved with 100% from LA 24 (weak) to LA 12 (very strong), the aggregate degradation will be reduced with about 50%. The Los Angeles test gives a fair ranking of rocks with regard to field performance (crushing), but is not able to reveal weathered rocks. The ballast layer can withstand around at least 40 tampings before it needs ballast cleaning (based on data from ERRI 1994).