Abstract: Resonance of multi-layer unsaturated railway ground induced by moving surface load is studied using a proposed semi-analytical approach. Influences of the soil saturation on ground vibrations are studied. The half space of railway ground is modelled as a layered unsaturated poroviscoelastic medium, the multiple Fourier transform method, the interface stress and displacement conditions for each soil layer are used to derive the global dynamic stiffness matrix of multi-layer unsaturated ground in the frequency-velocity domain based on the governing equations of unsaturated porous medium. A semi-analytical model for coupled track-ground is established by assembling a track model including a rail, rail pads, sleeper and ballast. The dynamic response of the multi-layer unsaturated ground caused by a moving harmonic load on the track is analysed. Considering the influences of the soil saturation on the soil shear modulus, the different dynamic response of the ground with various degrees of soil saturation for the surface layer and interlayer are discussed. The shading representation dispersion curves are used to study resonant modes for the unsaturated ground in the spectral domain. This research found that the influences of the soil saturation on ground displacements depend on soil layer properties, load speeds and frequencies. Besides, the ground saturation reduction can increase the appearance frequency of the ground resonant mode as well as the ground critical speed.

Key words: unsaturated railway ground, Fourier transform, ground vibration, critical velocity, dispersion curve