Insertion loss of vibration mitigation systems - methods of free field measurements with soil correction

摘要

The insertion loss describes the effectiveness of a vibration mitigation system as e.g. mass-spring systems, ballast mats or under sleeper pads. Measurements in free field can be done either as right/left or before/after method. In both cases two different situations are compared with the aim to get most comparable values for the vibration improvement at the relevant measuring points. Different soil conditions, geometric differences of compared sections, train variation and many other variations often make the comparison difficult, even nearly impossible. The different boundary conditions become more noticeable for smaller mitigation effects (e.g. under sleeper pads) than for high effective systems like mass-spring systems. A fundamental improvement of the results is obtained by taking into account the correct soil mobility at both measuring sections and the correct emission spectrum of the vibration source. The authors show insertion loss evaluations with and without soil correction for different mitigation systems. For soil correction the neighbored track or artificial excitation (impacts or shaker) can be used. Experiences of the presented method, advantages and disadvantages are shown with the help of practical examples. The shown methods will also be part of the new DIN45673-3-Spec "Experimental evaluation of insertion loss of mounted track systems".