Mechanical properties of railway ballast from laboratory tests

The findings of a series of isotropically consolidated, triaxial compression tests conducted at low confining pressures on model fractions of both fresh and recycled railway ballast have been used for the prediction of the shear strength of ballast. It is shown that the shear strength is a function of the particle size distribution and shape as well as the type of ballast. The effect of maximum principal stress ratio on the deformation and degradation of recycled material is also studied. It was observed that, at low levels of confining pressure typical to railway tracks, the variations of the angle of internal friction, dilation rate and the degree of particle crushing follow non-linear relationships with the confining pressure, at different principal stress ratios. A particle breakage index for ballast as a function of the maximum principal stress ratio, is introduced in this paper.