During the construction of road and railway infrastructure, there is a continuous need for the foundation of heavy structures and embankments on soft soils, or soils of inadequate bearing capacity. In such cases, some of the soil improvement methods such as stone columns or jet grouting are applied. An average increase of stiffness for the improved soil can successfully and reliably be determined by one of the non-destructive surface wave methods. The most common are: Spectral Analyses of Surface Waves, Continuous Surface Wave analysis, and Multichannel Analysis of Surface Waves. The methods are based on dispersive characteristics of Rayleigh waves, which consider surface waves of different wavelengths, i.e., frequencies, spread to different depths. Thus, waves of lower frequency, meaning of greater wavelength, are spreading deeper in the medium than waves of high frequency and smaller wavelength. The change of wave-spreading velocity on the surface depending on the wavelength is called wave dispersion and is closely related to the stiffness characteristics of a multi-layered medium through which the wave is spreading. The paper presents a detailed parametric analysis performed to identify the influence of a thin weak and stiff soil layer on the Rayleigh wave dispersion curve.

soil improvement; SASW; MASW; stiffness; dispersion curve