Experimental study on influences of scale effect on mechanical properties of railway ballast

For the purpose of studying the effects of particle size distribution (PSD) and scale effect on strength and deformation characteristics of the ballast, a series of triaxial shear tests based on 1/4 scaled ballast as well as full ballast are carried out using standard ballast of quartzite. In terms of the peak strength, the experimental results show that the peak strength of the scaled ballast is lower than that of the full ballast. Meanwhile, little effect on the peak strength caused by the scale effect can be observed from ballast with narrow gradation, whereas a significant decrease up to 10% of the peak strength can be found resulting from the scale effect from ballast with broad gradation. The strength indices of ballast, cohesion c and internal friction angle φ, are greatly affected by the PSD. However, the scale effect has little influences on the strength index. The difference in volumetric strain of the full and scaled ballasts is small as well as that in deformation modulus between broad and narrow gradations. The deformation modulus of scaled ballast is smaller than that of full ballast. The strength and deformation parameters of the scaled ballast can be used for engineering design, which are beneficial to engineering safety.