Determination of material damping in the soil based on the half-power bandwidth method and spatial decay of the Arias intensity in the SASW test

The Spectral Analysis of Surface Waves (SASW) method is wide ly used to determine the dynamic shear modulus and the material damping ratio of soils. It is based o n an in situ experiment where surface waves are generated by means of an impact hammer, a falling weight, or a hydraulic shaker. The resulting wave field is recorded by a number of sensors at the soil’s surf ace and used to determine dispersion and attenuation curves. An inverse problem is solved to identif y the corresponding shear wave velocity and the material damping ratio profiles: the (theoretical) disp er ion and attenuation curves are calculated for a given soil profile and compared to the corresponding (experi m ntal) curves derived from the surface wave test. The soil profile is subsequently adjusted in order to mi ni ize the distance between the experimental and the theoretical curves. This paper focuses on the determination of the material damp ing ratio of the soil by means of the SASW method. Two new methods to determine the material damping ra tio profile of the soil are presented, based on (1) the half-power bandwidth method and (2) the spatial de cay of the Arias intensity. The proposed methods to determine the material damping rati o are alternatives to existing techniques, where the amplitude spectrum of the wave field is used. Compar ed to the existing methods, both methods do not rely on the assumption that the wave field in the soil con sists of a single Rayleigh mode, which may lead to incorrect results when higher modes contribute to th e wave field. Both methods are successfully applied to a test site in Heverlee (Belgium).