Article

Predominant modes for Rayleigh wave propagation using dynamic stiffness matrix approach

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Abstract

In case of irregular dispersive media, a proper analysis of higher modes existing in a dispersion plot becomes essential for predicting the shear wave velocity profile of ground on the basis of surface wave tests. In such cases, an establishment of the predominant mode becomes quite important. In the current investigation for Rayleigh wave propagation, the predominant modes have been evaluated by maximizing the normalized vertical displacements along the free surface. Eigenvectors computed from the dynamic stiffness matrix (DSM) approach are analyzed to find the predominant mode. The results obtained are then compared with those reported in the literature. By varying the displacement amplitude ratios of the predominant mode to the other modes, dispersion plots have also been generated from the multichannel analysis of surface waves (MASW) method. The establishment of the predominant mode becomes especially significant, where usually only two to six sensors are employed and the governing (predominant) modal dispersion curve is usually observed rather than several multiple modes, which can be otherwise identified by using around 24 to 48 sensors.

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... Surface wave testing methods, namely, (i) spectral analysis of surface waves (SASW), and (ii) multichannel analysis of surface waves (MASW) are two non-intrusive and non-destructive techniques which are often employed to assess the shear wave velocity profile of ground and pavement sites (Nazarian and Desai, 1993;Park et al., 1998Park et al., , 1999Ivanov et. Al., 2011;Lin, 2014Naskar, 2017. These techniques are quite cost-effective and can be implemented very easily. ...
... performing an inversion analysis by matching the obtained field dispersion curve with that computed from the forward analysis so that an accurate prediction of the layered media can be ascertained (Kausel and Roёsset, 1981;Gucunski and Woods, 1992;Tokimatsu et al. 1992;Zomorodian et al., 2006;Naskar, 2015, 2017a;Naskar and Kumar, 2017). In the SASW tests, usually two to six sensors are employed for the procurement of the field data, and only the predominant/superposed mode of propagation can be noted in the dispersion plot (Tokimatsu et al., 1992). ...
... In the SASW tests, usually two to six sensors are employed for the procurement of the field data, and only the predominant/superposed mode of propagation can be noted in the dispersion plot (Tokimatsu et al., 1992). However, it is well understood that an interference of different modes can significantly vary the dispersion plots, and therefore, a prediction simply based on the employment of the predominant/superposed mode may lead to an erroneous result especially for an irregular dispersive ground profile (Kausel and Roёsset, 1981;Tokimatsu et al., 1992;Naskar and Kumar, 2017). On the other hand, depending upon acquisition geometry and velocity model, the MASW method can identify different modes to generate the experimental dispersion graph (Park et al., 1999). ...
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Spectral analysis of surface waves (SASW) is a nondestructive in-situ testing method that is used to determine stiffness profiles of soil and pavement sites based on dispersion characteristics of Rayleigh-type surface waves.Inversion of the Rayleigh wave dispersion curve of a site provides information on the variation of shear-wave velocity with depth. In the inversion procedures currently used for SASW tests, the field dispersion curve is matched with a theoretical dispersion curve obtained for the fundamental mode of surface wave propagation.In order to overcome difficulties associated with the presence of multi-modes in SASW signals, a new inversion method based on the maximum vertical flexibility coefficient is introduced in this paper. Unlike root-searching methods, the new method easily identifies the predominant propagation modes. In this new approach, the simplex method is used to match field and theoretical dispersion curves automatically. The purpose of this paper is to present the details of the new method and to demonstrate its advantages.
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Title from surrogate. "December 1984". Thesis (Ph.D.)--University of Texas at Austin, 1984.
Numerical and optimization techniques applied to surface waves for back calculation of layer moduli
  • Hossain
Surface wave methods: acquisition, processing and inversion Dottorato di Ricerca in Geoingegneria Ambientale Politecnico Di Torino
  • C Strobbia