Ballast/fines mixture is often found in railway substructure and the overall behaviour of tracks is strongly dependent on the mechanical behaviour of this mixture. Since directly testing such mixture with large grains is limited with common laboratory equipment, the consideration of a model material at smaller size is advisable. Parallel gradation method is widely used for this purpose. This study assesses the validity of this method in the case of ballast/fines mixture. Large-scale cyclic triaxial tests were carried out on the ballast/fines mixture at six volumetric coarse grain contents. The results obtained were analysed, together with those obtained previously from small-scale triaxial tests on a microballast/fines mixture whose microballast grain size distribution was determined by applying the parallel gradation method. The cyclic parameters (permanent strain and resilient modulus) were obtained for the two types of mixture. Results show that for all mixtures two distinct soil fabrics can be identified according to the variations of permanent strain and resilient modulus with the volumetric content of coarse grains f_v: a fine-fine contact structure for f_v ≤ 20% and a grain-grain contact structure for f_v ≥ 35%. In the case of fine-fine contact structure, the permanent strains and resilient modulus values of the ballast specimens are consistent with those of the microballast specimens, evidencing the validity of the parallel gradation method. In the case of grain-grain contact structure, the permanent strains and resilient modulus values are found to coincide globally at the two scales, also justifying the validity of the parallel gradation method, the slight differences between the two scales being attributed to the irregular grain sliding and the distribution of the fines soils.

镇流剂/细粉混合物通常在铁路子结构中发现，铁轨的总体性能在很大程度上取决于该混合物的机械性能。由于普通实验室设备限制了直接测试具有大颗粒的这种混合物，因此建议考虑使用较小尺寸的模型材料。为此，并行灰度法被广泛使用。这项研究评估了该方法在压载物/细粉混合物中的有效性。对压载物/细粉混合物在六个体积的粗粒含量下进行了大型循环三轴试验。将获得的结果与以前从小规模三轴试验中获得的结果进行了分析，这些结果是通过应用平行分级法确定了微镇流器/细粉混合物的微镇流器晶粒尺寸分布的。获得了两种类型混合物的循环参数（永久应变和弹性模量）。结果表明，对于所有混合物，根据永久应变和弹性模量随粗粒体积含量的变化，可以识别出两种不同的土壤织物˚F _v：用于细精细接触结构˚F _v  ≤20％，而晶粒晶粒接触结构˚F _v  ≥35％。在微细接触结构的情况下，压载试样的永久应变和弹性模量值与微压载试样的永久应变和弹性模量值一致，证明了平行渐变法的有效性。在晶粒-晶粒接触结构的情况下，发现永久应变和弹性模量值在两个尺度上全局一致，这也证明了平行渐变方法的有效性，两个尺度之间的细微差异归因于不规则晶粒滑移和细土的分布。