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Etude des processus d'instabilités des versants rocheux par prospection géophysique
- Apport du radar géologique -

Abstract : Rock cliff stability assessment is a complex problem, mainly due to the numerous failure mechanisms and to the lack of knowledge concerning the internal fracturing state of the rock mass. Geophysical methods can give information on the internal structure of a rock mass in terms of discontinuities. The Ground Penetrating Radar (GPR) is a very efficient method to detect and characterize the fractures. Multi-frequency GPR measurements (conventional 2D profiles, CMP and transmission data) are carried out on two vertical limestone cliffs near Grenoble. The results show that the 3D geometry of the fractures network can be retrieved by combining vertical and horizontal GPR profiles performed along the cliff. Velocity variations, deduced from CMP acquisitions can directly characterize large open fractures. Radar tomography provides 2D velocity images of the rock mass, but with a poor resolution. In a given frequency range, fractures detection by GPR depends on the opening and the filling, which control the reflection coefficient. A strategy for fractures characterization is proposed by using the frequencial sensitivity of the reflectivity. The inversion of the radar reflection coefficients, by using a Neighbourhood Algorithm, converges towards the correct parameters of the modelled fractures. The spectral ratio method, between a reflected signal (measured) and a reference signal (known) allows to easily calculate the reflection coefficient. A numerical 2D study (FDTD) is carried out in order to choose the reference signal. The inversion of the synthetic reflection coefficients, tested for an open fracture configuration observed on a studied site, permits to validate the method.
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Contributor : Mathieu Jeannin Connect in order to contact the contributor
Submitted on : Tuesday, April 25, 2006 - 2:05:25 PM
Last modification on : Friday, September 30, 2022 - 4:09:24 AM
Long-term archiving on: : Saturday, April 3, 2010 - 9:56:02 PM


  • HAL Id : tel-00012178, version 1



Mathieu Jeannin. Etude des processus d'instabilités des versants rocheux par prospection géophysique
- Apport du radar géologique -. Géophysique [physics.geo-ph]. Université Joseph-Fourier - Grenoble I, 2005. Français. ⟨NNT : ⟩. ⟨tel-00012178⟩



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