Ballast loading plate design and mechanical behavior of under ballast mats

•Distribution pattern of ballast indentation at the bottom of a trackbed was obtained.•Contact and stress transfer between the ballast and ABP, GBP, and FP were analyzed.•ABP is suggested to replace the GBP of European standards EN17282 and EN16730.•UBMs of different stiffnesses were studied using different loading methods. Geometry of loading plate which simulates the ballast contacting interaction is the critical factor for mechanical properties and durability test of the geotextile for railway track. In this study, a ballast indentation test with 3D laser scanning method was performed to study the actual contact characteristics of the bottom of the ballast. Based on this, the existing problems of geometric-ballast-plate (GBP) of the EN standard were presented. Therefore, a new ballast loading plate, Actual Ballast Plate (ABP), was designed and verified. The mechanical behavior of under ballast mats (UBMs) with different stiffnesses were studied by applying different ballast loading plates (the ABP, GBP, and flat plate). Results demonstrated that for the GBP, the geometric characteristics of sharp corners at the bottom of the ballast were largely overlooked, resulting in smaller contact stress in the fatigue test. The ABP resulted in a better simulation of the contact characteristics and load transfer relationship of the ballast. The stiffness test with the flat plate (FP) and GBP resulted in a higher static modulus for the hard UBM because of the overestimation of the contact area between the UBM and the ballast. It is recommended that the EN standards adopt the ABP to replace the GBP for the fatigue tests of the UBMs.