Experimental Updating of Soil Profiles through the Spatial Phase Dispersion of Surface Waves

MARCELO A. CEBALLOS, CARLOS A. PRATO

Nantes, Francia

Simposio; 7th International Symposium on Non Destructive Testing in Civil Engineering; 2009

French Confederation of Non Destructive Testing (COFREND)

The mechanical characterization of soil profiles by means of the Spectral Analysis of Surface Waves (SASW) has become a widely accepted practice in recent years. This technique presents some limitations inherent to the hypotheses adopted in establishing the analytical dispersion curve used for the adjustment of the soil profile model. It relies on the adjustment of the fundamental propagation mode and thus lacks capacity to identify the presence of soft layers located under stiffer strata, where higher surface wave modes are generally excited. The experimental dispersion curve is affected by the variation of the "effective" velocity of the profile, which depends on the propagation modes involved and on the location of the transducers. This work presents a multiple transducers experimental technique based on a target function with two independent variables: the input frequency of the source and the propagation velocity of the surface waves. This function, herein referred to as "spatial phase dispersion", presents minimum values for frequencies and propagation velocities closely related with the dispersion curve of the SASW technique. A least square minimization between experimental and analytical spatial phase dispersion allows parameter adjustment of soil profiles even in cases of soft layers underlying stiffer strata. The variability of the effective velocity is explicitly considered during the model updating. Sample real cases are presented in order to show the performance of the proposed procedure.