## 4 Measurement Results
### Measurements Related to Under-Sleeper Pads  
Three measurement campaigns about under-sleeper pads were performed during the RIVAS project [4; 14; 19]. At first, a measurement site near Regensburg with six track sections equipped with three different under-sleeper pads were investigated where the nominal static stiffnesses were 0.10, 0.15 and 0.22 N/mm\({}^{3}\). The ground vibration at the reference section without under-sleeper pad are shown in Figure 3(a) for an ICE train. For all distances to the track, the dominant frequencies can be found around 16 Hz and at 64 Hz. Similar results are presented in Figure 3(b) for one of the sections with under-sleeper pads. The maximum around 16 Hz is still present (somewhat reduced at the far field), but the peak at 64 Hz (the sleeper-passage component) is almost completely missing. The ground vibration reduction \(v_{I}/v_{U}\) between the isolated and the un-isolated track (Figure 3(c)) clearly presents this effect and some smaller effects at high frequencies. The second measurements were performed near the villages Lengnau and Pieterlen in Switzerland where three different under-sleeper pads with a nominal stiffness of 0.12 N/mm\({}^{3}\) have been installed at a straight and a curved track. The ground vibration near the un-isolated reference track and one of the isolated tracks are shown in Figure 5. The reference track (Figure 4(a)) shows a dominating low-frequency part at 12 to 16 Hz which is clearly reduced by the under-sleeper pads (Figure 4(b)). The high frequency maximum at 50 to 60 Hz, therefore, is more dominant for the isolated track, and the vehicle-track resonance may be expected here. The higher frequencies are then also reduced by the under-sleeper pads (Figure 4(c)). The measurements of all sections at the Lengnau site have been evaluated for an average reduction in [19] (Figure 6, triangle markers). These results are presented together with three more measurements of under-sleeper pads at Timelkam in Austria from [20] and at Sempach in Switzerland [21]. The high-frequency reduction is between 10 and 15 dB in fair agreement with the softness of the under-sleeper pads which have static stiffnesses of 0.1, 0.15, 0.17, and 0.3 N/mm\({}^{3}\). All these measurements show also a low-frequency reduction of 5 to 15 dB. Figure 4: Under-sleeper pads at the Regensburg site; measured ground vibration at distances of \(\square\) 8, \(\Circle\) 12, \(\Circle\) 16, + 24, \(\times\) 32, \(\Diamond\) 48, \(\times\) 64 m from (**a**) the reference track, (**b**) a track with under-sleeper pads, and (**c**) average ground vibration reduction for three different track sections. Finally, newly designed tracks have been installed in Herne at Eiffage Rail. Wide and heavy sleepers from Rail One have been equipped with very soft under-sleeper pads with a static stiffness of 0.03, 0.06, and 0.10 N/mm\({}^{3}\). The ten different tracks were excited by a special fixed (non-moving) shaker and an additional static load. The results for the reduction of the ground vibration are shown in Figure 7a. Figure 7b shows calculations from BAM where the nominal track parameters were adjusted to the measurements. The high-frequency reduction was clearly found for all isolated solutions. The reduction starts at a frequency which depends on the stiffness of the under-sleeper pad and lies between 32 and 64 Hz. As the shaker simulates the mass and load distribution of a bogie, this resonance frequency is also expected for a running train. The softest under-sleeper pads yield the lowest resonance frequency and the strongest reduction of up to 20 dB. Because of the fixed (non-moving) excitation, there are no impulses from the passing static loads, and no low-frequency reduction can be found.