Numerical Investigation of Impedance Variation Effect on Surface-Waves’ Propagation for Characterization of Very Soft Soils

F. Díaz-Durán, G. Cascante, M. Pandey

In the proceedings of: GeoEdmonton 2018: 71st Canadian Geotechnical Conference; 13th joint with IAH-CNC

Session: Peats and Soft Soils

ABSTRACT: The characterization of soils by using near-surface geophysical techniques has been gaining attention in the geotechnical engineering practice in the last two decades. The multi-channel analysis of surface waves (MASW) is a geophysical technique for profiling shear wave velocity in a soil by applying inversion techniques from the dispersion curve. Numerical simulations were performed to understand the limitations of MASW technique when characterizing very-soft soils. Results show that shear wave velocities and layer thicknesses of very-soft materials can be estimated with uncertainty about 2%. However, the acoustic impedance ratio between adjacent soil layers has effect in the MASW results interpretation. From the results it is possible to conclude that the lower the impedance ratio the higher the diffusion of seismic energy. Based on these results it is possible to define a threshold value for the impedance ratio beyond which the use of MASW technique becomes unfeasible to characterize very-soft soils.

RÉSUMÉ: La caractérisation des sols en utilisant des techniques géophysiques proches de la surface a attiré l'attention dans la pratique de l'ingénierie géotechnique au cours des deux dernières décennies. L'analyse multicanal des ondes de surface (MASW) est une technique géophysique pour profiler la vitesse d de cisaillement dans un sol en appliquant des techniques d'inversion à partir de la courbe de dispersion. Des simulations numériques ont été réalisées pour comprendre les limites de la technique MASW lors de la caractérisation de sols très mous. Le rapport d'impédance acoustique entre les couches de sol adjacentes a un effet sur l'interprétation des résultats MASW. A partir des résultats, il est possible de conclure que plus le rapport d'impédance est faible, plus la diffusion de l'énergie sismique est élevée. Ainsi, il est possible de définir une valeur seuil pour le rapport d'impédance au-delà duquel l'utilisation de la technique MASW devient impossible pour caractériser les sols très mous.

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Cite this article:
F. Díaz-Durán; G. Cascante; M. Pandey (2018) Numerical Investigation of Impedance Variation Effect on Surface-Waves’ Propagation for Characterization of Very Soft Soils in GEO2018. Ottawa, Ontario: Canadian Geotechnical Society.

@article{geo2018Paper390,author = F. Díaz-Durán; G. Cascante; M. Pandey,title = Numerical Investigation of Impedance Variation Effect on Surface-Waves’ Propagation for Characterization of Very Soft Soils ,year = 2018}