Can We Really Detect Cavities Using Seismic Surface Wave?

Abstract : Shallow cavities, such as karstic caves in carbonate bedrock, near-surface underground mine workings and tunnels, constitute serious hazards for people and existing constructions due to the risk of collapse and subsidence. This phenomena is growing fast with climate change involving damages to buildings and increasing urban development costs. Karstic features, voids, surficial dissolution, alteration and unconsolidated material are thus major challenges for geophysical methods which could play a major role for their detection. Recent investigations have reported good results for cavity imaging using surface wave seismic methods (Sloan et al. 2015, Samyn et al., 2013, Leparoux et al., 2000, Nasseri-Moghaddam et al. 2005, Gucunski et al., 1996, Park et al. 1996). But in spite of successful case histories, business as usual void detection is still challenging due to the complexity of near surface materials and probably the limited resolution of geophysical methods. The propagation of Rayleigh waves in homogeneous layered media is well understood and has been addressed in depth by several authors (Thomson 1950, Haskel 1953, Graf 1975). The derivation of analytical solutions for the scattering of Rayleigh waves around heterogeneities is complicated and researchers often perform experimental tests or develop numerical models to study this problem (Gelis et al. 2005, Gucunski et al. 1996). These numerical studies have shown reflections from the heterogeneities (even in the cavities) and perturbations in the dispersion curves. Leparoux et al. (2000) applied the MASW test to locate two cavities: masonry at 3.0 m below the ground surface, and the other one embedded at about 8.0 m beneath the surface, without masonry. Xia at al. (2007) demonstrated using 2-D surface wave modeling that the diffractions due to a void on a homogenous half space were Raleigh-wave diffractions because of their amplitude, velocity, and frequency. They derived a travel-time equation of surface wave diffractions based on properties of surface wave and solved this equation for a phase velocity and depth to a void. Sloan et al. (2015) demonstrated the capability of using P-wave diffraction and surface wave backscatter techniques to detect subterranean tunnels. Despite these convincing arguments, we have been recently confronted to disheartening results leading us to the question: Can we really detect cavities using seismic surface wave? The objective of this study is to pose the problem for understanding interaction between a cavity and a Rayleigh wave by measuring the wave field in surface on the roof and on the floor of a known cavity. For addressing this issue, we have focussed on a study area located in Souzay-Champigny, France. This consists of an abandoned underground quarry network in cretaceous chalky limestone (Bitri et al. 2014). We have chosen these cavities because they are accessible underground and partly mapped.
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Communication dans un congrès
22nd European Meeting of Environmental and Engineering Geophysics : Near Surface Geoscience 2016, Sep 2016, Barcelone, Spain. 2016
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Adnand Bitri, Kevin Samyn, C. Filippi. Can We Really Detect Cavities Using Seismic Surface Wave?. 22nd European Meeting of Environmental and Engineering Geophysics : Near Surface Geoscience 2016, Sep 2016, Barcelone, Spain. 2016. 〈hal-01371628〉

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