The Excitation, Propagation and Mitigation of Train-Induced Ground Vibrations from the Axle Impulses on the Track

Train-induced vibrations in soft ground usually have a strong low-frequency component.This component has a characteristic spectrum which is related to the axle sequence and the speed of the train.Its attenuation with distance is weaker than the attenuation for higher frequencies, and it always dominates the far-field ground vibration.Narrow-band frequency analyses clearly show that this ground vibration component is due to the static axle loads.Axle box vibrations have a different characteristic where the first out-of-roundness of the wheels is the only remarkable low-frequency component.Therefore, the dynamic axle loads from wheel and track irregularities are not the reason for the strong ground vibration component.The moving static axle loads generate the quasi-static response of the soil at very low frequencies and at very near distances.A part of the original impulse spectrum is scattered when it propagates through an inhomogeneous ballast and soil with a randomly varying stiffness.The axle impulses are smoother for a higher bending stiffness or a lower support stiffness (under sleeper pads, under ballast mats) of the track.This mitigation of the ground vibration will be demonstrated by measurements at three sites in Switzerland as well as the characteristic of the soil and axle-box vibrations.