1st Proctor Lecture of ISSMGE: Railroad performance with special reference to ballast and substructure characteristics
Ballasted rail tracks are widely used throughout the world because they are economical, readily drained, and have sufficient load bearing capacity. Despite these advantages, geotechnical concerns such as ballast degradation, fouling (e.g. coal and subgrade soil), poor drainage of soft subgrade, pumping of clayey subgrade, differential track settlement and track misalignment due to excessive lateral movements exacerbate the cost of track maintenance. Globally, billions of dollars are spent annually on the construction and maintenance of rail tracks. Existing industry design standards are often unable to address these problems because they ignore true cyclic loading patterns, track vibrations, and the onset of plasticity and degradation of track materials. The mechanisms of ballast breakage and deformation, understanding the interface behaviour using geosynthetics, the need for effective track confinement using geocells, time-dependent drainage and filtration properties of track materials require further research to improve existing design guidelines. In view of this, large scale laboratory tests have been carried out using state-of-the-art facilities designed and built at the University of Wollongong and in other proactive rail institutes worldwide in Europe, America, Japan and China. Based on these tests, various factors governing the stress-strain behaviour of ballast, the strength and degradation of ballast, the ability of various geosynthetics and synthetic energy absorbing mats to minimise ballast breakage and track settlement, the effectiveness of subballast as a granular filter and its stabilisation with geocell have been analysed. In Australia, field studies on instrumented tracks at Bulli (near Wollongong), Singleton and Sandgate (near Newcastle), have been carried out to assess the performance of railroad embankments stabilised with geosynthetic grids, rubber mats, and prefabricated vertical drains. This inaugural Ralph Proctor Lecture focuses on the current state of research encompassing deformation and degradation assessment of railroads and the benefits of geo-inclusions, highlighting examples of innovations from theory to practice, predominantly based on the own experience of the Author.