Rayleigh wave propagation assessment for transport corridors

Wheel loading from high-speed trains can generate seismic ‘Rayleigh’ waves that propagate in the near surface, causing track and ground displacements. These displacements can increase over low-density, poorly consolidated soils with low wave velocities. Rayleigh wave characteristics were mapped onto soil engineering geological classifications using lithological and density parameters in effective stress-based algorithms that model shear wave velocities with depth. The use of small-scale engineering geological maps and one-dimensional modelling identified low Rayleigh wave velocity profiles associated with alluvial and terrace deposits in river catchments and floodplains along the proposed High Speed 2 route in the UK. Examination of the velocity−depth profiles indicated that sites are especially susceptible to dynamic displacement amplification where train-induced ground motion occurs within an interval of up to half the wavelength of the Rayleigh wave frequency induced by the train load centres. Using the algorithms to attribute density and shear wave velocities to the engineering geological section, a two-dimensional ground model was created for an alluvial-terrace structure at Perivale. Wave propagation modelling using a finite-difference code indicated amplification due to interference effects from wave fronts that propagated along different pathways of up to 2 times on vertical and 2·5 times on the horizontal displacement.