Cyrille Fauchard

Detection of Leakage Areas in an Earth Embankment from GPR Measurements and Permeability Logging

Ground penetrating radar (GPR) is a nondestructive method allowing the improvement of our knowledge of civil engineering structures. In particular, this method may be a nondestructive efficient tool for dike diagnosis and complete classical geotechnical methods. In this paper, we present GPR observations obtained on an earth embankment (crest and sloped paved revetment) in bad condition and located on the lateral canal of the Loire river (Saint Firmin, 80 km South East of Orleans). These measurements are combined with corings, visual inspection, and permeability logging performed with an updated drilling system, the Permeafor. This survey leads (i) to the detection of decompressed zones associated with leakage areas visible at the foot of the downstream slope and (ii) to the location of potentials voids underneath the paved revetment. This multidisciplinary approach complied with the dike inspection methodology proves its efficiency for the assessment of earth embankments.

Detecting Unbounded Interface with Non Destructive Techniques

The French road network has been built more than 30 years ago, and consists mainly of bituminous pavements. Some of them have also been maintained several times by thin overlays. On these pavements, a lot of damage such as potholes and alligator cracking has been observed, in particular after periods of heavy rain or freeze/thaw. Frequently, this type of damage is assumed to be linked with interface debonding between these overlays and the old pavement, associated with moisture effects. To detect such damages, some non destructive techniques (NDT), as electromagnetic techniques (GPR, step-frequency radar or infra-red) or as mechanical techniques (from static deflection measurements to seismic wave propagation methods), appear as promising approaches. This paper compares two differents NDT to detect debonding during an experiment carried out on the large pavement fatigue carrousel of IFSTTAR in Nantes.

FDTD Modeling of a Resistively Loaded Monopole for Narrow Borehole Ground Penetrating Radar

The geometryof a broadband (0.7-2 GHz) monopole antenna intended to be inserted in a narrow borehole for ground penetrating crosshole application is proposed. The monopole antenna is supposed to be designed on a printed circuit board (PCB) using the low-cost microstrip technology. Based on the FDTD approach, the modeling of the antenna surrounded byits environment has been made, and the influence of several parameters on the radiated waveforms has been studied in details. The modeling of a transmission link has also been considered. Such a studyaims at the realization of a narrow broadband antenna.

Methodology Applied to the Diagnosis and Monitoring of Dikes and Dams

The recent and dramatic floods of the last years in Europe (Windstorm Xynthia, February 2010) and United-States (Hurricane Katrina, August 2005) showed the vulnerability of flood defence systems. The first key point for avoiding these dramatic damages and the high cost of a failure and its consequences lies in the conception and construction of the dams and dikes, taking into account the past flooding events. A well-designed dike with the correct height avoids failure and overtopping.

Resistivity/Induced Polarization/Self-Potential Methods and Applications

Modern multielectrode and multichannel resistivity systems have made it relatively easy and rapid to collect time domain induced polarization (IP) data in near surface surveys. This paper will examine a wide variety of applications through case studies in a variety of geological settings in Western Canada. Case studies will show various applications and complementary features of IP surveys including distinguishing salt water from conductive clays, identifying faults, locating deeply buried structures underneath active facilities, and distinguishing landfilled debris from leachate. IP data sets will be correlated with other data sets including resistivity, seismic reflection, and borehole geophysical parameters.

Contribution of SFM and ERI Methods to Assess an Underground Quarry Pillar

Natural degradation of underground quarries is a major issue from an economic and public safety point of view. Electrical Resistivity Imaging (ERI) method can assess efficiently the electrical resistivity distribution inside a medium and its evolution. However, conventional 3D ERI methods are not well suited for quarry pillar assessment. Moreover, a complete 3D ERI necessitates an accurate 3D geometry. In this paper, we propose the use of cost effective SFM techniques to generate a three-dimensional medium. A new assessment methodology based on the combination of SFM and Electrical Resistivity methods is proposed. This methodology is applied to a real limestone quarry pillar. Inversion results show the key role of the accuracy of the 3D model.