Shear Behavior of Railway Ballast Based on Large-Scale Triaxial Tests

Quarried rock fragments (ballast) constitute one of the most commonly used construction materials in railway engineering practice. Ballast is subjected to high stress levels as well as being always exposed to environmental changes. Unsatisfactory performance of railway tracks is often associated with the loss of cross level, track profile and track alignment. The in situ condition and the engineering behavior of ballast are also important aspects governing the stability and performance of a given railway track structure. This paper presents the findings of a series of isotropically consolidated, triaxial compression tests on two modeled fractions of uniformly graded latite basalt, which is currently being used by the Railway Services Authority (RSA) of New South Wales, Australia, in the construction of new railway tracks. These tests form part of an extended research program sponsored by RSA to study the stress-strain relationships, strength properties and degradation characteristics of various types of railway ballast. The program is associated with the necessity of upgrading railway tracks for the looming Olympics in 2000. Large-scale triaxial equipment has been employed during the testing program, which is formulated to provide specific geotechnical information on the shear strength and the angle of internal friction of ballast as a function of the particle size distribution. The effect of maximum principal stress ratio on the deformation and degradation of ballast is also studied. Nonlinear relationships are developed to describe appropriately the variation of shear strength, angle of internal friction, dilation rate and degree of particle crushing at different confining pressures and principal stress ratios.