Triaxial Tests on Dolomite Railroad Ballast

Triaxial static compression and extension tests using low confining pressures have been performed on a fine mineral grained tough dolomite railroad ballast. The shear strength and tangent modulus increased significantly with both confining pressure and density increase, indicating the importance of both crib depth and compaction in maintaining the stability of unloaded track (i.e., preventing sun kinks). Of particular importance is the high apparent cohesion at the low cell pressure in comparison with tests reported elsewhere on sands and rounded gravels indicating the importance of a high percentage of crushed faces which is contrary to tests reported by others at high cell pressures where crushed material has lower strengths. A similar contradiction was also noted for particle size. Comparison with other results indicates larger particles probably give higher strengths at low cell pressures. The volume and axial strains are also reported in terms of initial pseudo-Poisson's ratio and in terms of stress dilatancy.