Blind field tests to determine Rayleigh wave velocity on a high-speed railway environment: The reliability of seismic surface waves methods

To ensure track stability and good earthwork performance for high-speed railways the surface wave velocity in the earthworks should exceed the train's speed. Specifications for high-speed rail are now stating minimum Rayleigh wave (VR) velocities to be checked during construction. This requires suitable reliable geophysical tests, however there are no defined standards or data collection and processing protocols. Additionally, the analysis of these data traditionally relies on the practice and experience of those undertaking the work which can introduce variability in results. This paper presents the results of a blind comparison trial investigating Multichannel Analysis of Surface Waves test (MASW) for use in high-speed rail earthworks compliance evaluation, concentrating on assessment of Rayleigh wave velocity (VR). Testing was undertaken by four companies, at the same site on natural ground and a stabilised trial embankment. Defined tests protocols and a test of their own design against a specification to assess VR were used. The anonymised VR results show reasonable agreement in the dispersive character of the soil if higher modes are carefully considered when picking a dispersion curve. The VR results were then investigated against depth using a rule of thumb. Such an approach avoids the inversion processing step (to get more traditional Vs against depth) which potentially introduces variability. This suggests that direct Rayleigh wave data could be used by earthworks engineers to give routine compliance assessment and then if required further investigation undertaken in areas of compliance concern within the overall earthwork.