Large-scale direct shear tests on sand-contaminated ballast

Abstract

Significant parts of railway lines in most of the Middle East and Asian countries are in sandy and desert areas. Contamination of tracks (in particular the ballast layer) caused by frequent sand storms in the desert is an important challenge for railway industries. Despite a large number of reported railway accidents caused by the loss of shear strength in the contaminated ballast layer, there is a lack of sufficient studies on the effect of sand contamination on ballast shear strength. In response to this need, extensive laboratory tests on clean and sand-contaminated ballasts were conducted, using a large-scale direct shear test machine designed and constructed in this research. Ballast samples with different dosages of sand contamination were tested. The results obtained are discussed leading to a better understanding of ballast behaviour when contaminated with various amounts of sand. The results show that sand contamination reduces the shear strength and angle of effective shearing resistance of the ballast. The critical percentage of ballast contamination, after which the ballast faces substantial reduction in its mechanical properties, was derived. The results obtained have improved the current ballast maintenance approach by providing the possibility of a more accurate planning of ballast cleaning and renewals.