Mechanical properties of reused ballast

It is generally accepted that railway ballast has a finite life. With use it becomes abraded and fouled, and is eventually cleaned and replaced or often renewed completely. However, much of our experience regarding the gradual deterioration of railway ballast is based on aggregates (e.g. limestone) that are mineralogically more susceptible to damage than the high quality granite used on a modern railway. Building on previous work, this project will investigate the extent of, and the reasons for, the apparent deterioration due to traffic and tamping in the mechanical properties of ballast of different mineralogies (granite and limestone), fresh and used ballast (from sites and from the laboratory rigs), cleaned ballast (from the ballast cleaning train) and modified cleaned ballast, by means of
a. monotonic and cyclic triaxial tests on full size and scaled ballasts
b. rig tests at Southampton and Nottingham, using full size ballast
c. field data of ongoing settlements and lateral movements before and after renewals where no additional interventions (apart from reballasting and track renewal) have been carried out, from the T2F field study sites
d. numerical discrete element analysis (DEM) to explore the fundamental mechanisms responsible for any deterioration in ballast performance (e.g. attrition, loss of surface roughness, increasing particle roundness, change in PSD)