Use of surface waves and seismic refraction for the inspection of circular concrete structures

In this paper, the propagation of both longitudinal and surface waves will be investigated within the scope of seismic measurements recorded along the circumference of concave structures. The underlying objective herein is to recover, in a non-destructive manner, the mechanical material properties from seismic refraction as well as multiple-channel analysis of surface wave measurements. This experimental set-up along the circumference is currently employed in the case of circular concrete tunnels or shafts when sensors cannot be installed along the structural baseline. The influence of curvature on longitudinal wave propagation will first be quantified by means of a simple analytical model. If curvature is neglected, the thickness of a damaged concrete cover will be overestimated, whereas its longitudinal wave propagation velocity will be underestimated. For surface waves, it will be shown that the influence of curvature exerts a major impact on phase velocity, which cannot be incorporated into the classical multiple-channel analysis of the surface wave forward problem. Consequently, we have developed a numerical model dedicated to such geometries that relies upon complex values of the surface wave phase velocity. The first part of this article is dedicated to the description of the mathematical derivation of the propagation of surfaces wave in a curved medium. This numerical model is then compared with experimental data recorded on a reduced-scale concrete tunnel of metric size. The agreement between experimental and numerical results, as well as seismic refraction and the multiple-channel analysis of surface wave complementarity, form the basis of an in situ, non-destructive testing technique.