Estimating rock properties using seismic refraction survey data: a case study in an abandoned road tunnel. Issue 4 (4th July 2021)

• Record Type: Journal Article
• Authors: Izumotani, Satoshi; Takeuchi, Mutsuo; Murayama, Hideyuki; Okazaki, Kenji
• Is Part Of: Exploration geophysics. Volume 52:Issue 4(2021)
• Page Start: 409
• Page End: 418
• Publication Date: 2021-07-04
• Subjects: Seismic refraction -- velocity -- porosity -- rock physics -- geotechnical geophysics -- near tunnel; Geophysics -- Periodicals; Prospecting -- Geophysical methods -- Periodicals; 622.15
• DOI: 10.1080/08123985.2020.1828856
• Languages: English
• ISSNs: 0812-3985

Abstract

Abstract : We propose a new interpretation procedure based on Gassmann's theory, to estimate rock properties from seismic P-wave velocity ( Vp ) and S-wave velocity ( Vs ) data, mainly for near-surface applications. Rock properties estimated in the procedure are porosity, water saturation, and clay content of rock. Water saturation is first estimated by an analysis of a cross-plot of Vp /Vs and S-wave velocity, based on the concepts of mudrock and dry lines proposed by Castagna et al. [1985. Relationships between compressional-wave and shear-wave velocities in clastic silicate rocks. Geophysics 50: 571–81]. Porosity is then estimated using the extended existing empirical equations. Clay content is estimated from an analysis of the cross-plot of shear modulus and porosity. Finally, effective porosity is estimated using porosity and clay content. We tested this procedure with seismic data acquired in a tunnel abandoned due to deformation of the tunnel walls and to many water leakages. P-wave and S-wave velocity profiles, obtained from a 1, 500 m long seismic refraction survey on a paved road in the tunnel, were used to estimate porosity, water saturation, and clay content of the rocks surrounding the tunnel. Rock property estimates were compared to geotechnical observations and measurements in the tunnel, such as deformation of the tunnel walls and water leakage sites. The results of these comparisons revealed that estimated rock property profiles can be used effectively to identify cracks within the rock and fluids in the pores of the rocks around the tunnel. This study demonstrates that the proposed procedure for estimating rock properties from seismic data is a promising technique for visualising subsurface rock properties for shallow engineering applications.