Effect of Flakiness-Elongation Index on Shear Behavior of Railway Ballast

In order to investigate the influences of flat and (or) elongated ballasts on direct shear mechanical properties considering the breakage effect, the direct shear tests with different test conditions were conducted to study the effect of the flat and/or elongated ballast content with the analysis of testing results from the ballast shear strength, deformation and breakage. The results show that: (1) With the increase of the flakiness and elongation index, the shear behavior of the ballast decreases, both the shear strength and internal friction angle (at 100 kPa, the shear strength respectively decreases by 10.9%, 16.8% when the elongation index increases from 0 to 20%, 40%; the shear strength respectively decreases by 14.7%, 22.3% when the flakiness index increases from 0 to 20%, 40%; the shear strength respectively decreases by 12.4%, 18.9% when the flakiness-elongation index increases from 0 to 20%, 40%). (2) The shear dilatation and shrinkage of samples decrease with the flat and/or elongated ballast content increasing. (3) The flat and elongated ballast particles are prone to break up during the direct shear test, and most of them are fractured with the sharp corner breakage, which significantly affects the ballast bed maintenance cycle.