Publication Date:
2004
Description:
One of the recurring problems in civil engineering and landscape management
is the detection of natural and man-made cavities in order to mitigate the problems of
collapse and subsurface subsidence. In general, the position of the cavities is not
known, either because they are not recorded in a database or because location maps are
not available. In such cases, geophysical methods can provide an effective alternative
for cavity detection, particularly ground-penetrating radar (GPR) and seismic methods,
for which pertinent results have been recently obtained. Many studies carried out under
real conditions have revealed that the signatures derived from interaction between
seismic signals and voids are affected by complex geology, thus making them difficult to
interpret. We decided to analyze this interaction under physical conditions as simple as
possible, i.e., at a test site built specifically for that purpose. The test site was
constructed of a homogeneous material and a void-equivalent body so that the ratio
between wavelength and heterogeneity size was compatible with that encountered in
reality. Numerical modeling was initially used to understand wave interaction with the
body, prior to the design of various data-processing protocols. P-wave imagery and
surface-wave sections were then acquired and processed. The work involved in this
experiment and the associated results are presented, followed by a discussion concerning
the reliability of such a study, and its consequences for future seismic projects.
Keywords:
Seismics (controlled source seismology)
;
Engineering geophys.
;
P-waves
;
Surface waves
;
GPR
;
seismic
;
imaging
;
surface
;
waves
;
cavity