Low-frequency ground vibrations from underground trains

In the present work, the ground vibrations generated by underground trains are investigated theoretically in the low-frequency approximation, i.e. for characteristic wave-lengths of generated bulk acoustic waves in the grountl being essentially larger than the diameter of the tunnel. The Green's function Jbrmalism is appliej to calculate contributions of all sleepers of the track located inside the tunnel antl subjected to the action of a quasi-static pressure from all wheel axles. parameters of a train, track and a tunnel as well as mechanical properties of soil (including contact nonlinearity of the track-soil system) are being taken into account. The correspontling numerical calculations show that for most of the practical values of a tunnel depth, the main contribution to the vertical component ofthe sutface grourul vibration velocity is due to the radiated shear bulk waves rather than to the ktngitudinal ones. Comparison of the ground vibration spectra generated by typical underground trains with the spectra of the above-ground trains shows that the shapes of these spectra are similar. This implie:s thal one can use for underground trains the same methods of suppressing ground vibrations at speed-dependent frequencies that can be usetl for above-ground trains, e.9., by choosing special relations between the track and train parameters.