Safety while tunneling is one of the main challenges for underground constructions, avoiding
confinement losses, which remain an important risk for public works, leading to additional delays and high
insurance costs. In such applications, usual surface instrumentations cannot be set up because of high building
density in many overcrowded cities. Tunnelling deals with the challenge of requiring ground surface
undisturbed. One original concept proposed in the framework of the European Tunconstruct project, consists
in very early settlement detection close to the tunnel vault and before any detectable effect on the surface. The
adopted solution is to set-up a sensing element inserted into a directional drilling excavated above the
foreseen tunnel. The methodology is based on the well known Brillouin Optical Time Domain Reflectometry
(B-OTDR) in singlemode optical fibres and a special cable design dedicated to bending measurement. Two
cables, based on different industrial manufacturing processes, have been developed taking into account the
strain sensitivity required, the flexibility and the robustness for borehole installation, a low power attenuation
and storage on a drum. Industrial prototypes have been manufactured and validated with tests in open air
where settlement profiles geometry can be accurately controlled. Demonstration on job site took place on The
Greater Cairo Metro Line 3 (CML3) at the beginning of 2009.
The thermal drift of the characteristic wavelength of a Fiber Bragg Grating photowritten in the core of an 18-hole-microstructured
fiber is significantly reduced by inserting a liquid of suitable refractive index into its holes. The
maximum sensitivity is reduced, and the spectral range of variations is divided by a factor of 8, over a temperature range
larger than 20°C. Such passive FBG temperature compensation technique is of great interest for applications involving
accurate sensing free of thermal effects.
In-situ thermal measurements of argillaceous rocks is required by the ANDRA to evaluate the feasibility and dimensioning of a long-life radioactive waste storage in deep geological underground repository sites. The last large scale experiment called HE-D has started in the middle of 2004 in the Mont Terri Underground Rock Laboratory based in Switzerland to evaluate new kinds of thermal instrumentations and improve the understanding of the thermal conductivity coefficient of the Opalinus clay. A thermal cane equipped with 6 optical Fiber Bragg Grating sensors (FBGs) has been developed by the CEA-List and installed in a 15 m-long borehole surrounding a central heating borehole. The sensitivity and thermal transduction of FBG sensor packaging have been characterized in laboratory before installation. Mechanically, the robustness of FBG packaging has been validated during the introduction in the borehole and the two measurement campaigns respectively four and nine months thereafter. In this paper, we report the results of the FBG temperature measurements in comparison with traditional resistive probes (Pt100) at different stages of the experiment. The temperature accuracy and resolution obtained in the laboratory are better than 0.2°C and 0.1°C respectively. In the borehole, the differences between both kinds of sensors were no more than 0.2°C.
In this paper we present results relative to Fiber Bragg Grating (FBG) photowritten in two kinds of Ge-doped microstructured optical fiber cores devoted to sensing applications. A cross-comparison between theoretical and experimental modal field patterns is carried out. We present the first values of spectral sensitivity of Bragg grating in relation to the refractive index of the substance inserted into the holes.
This paper describes the laboratory tests and field trial on the Saint-Jean bridge (Bordeaux, France) of both FBG extensometers (long and short-gage) and associated instrumentation, in the context of its industrial transfer.
Most civil engineering structures have been built in the 50's and 60's and reach similar level of degradation accelerated by loading conditions and corrosion. In Europe, National Authorities and the European Commission promote Health Monitoring concepts, instrumentation of existing structures and help in the design of new durable structures of higher performance. In this context, the CEA-List has achieved a non-exclusive industrial transfer of its Bragg grating sensing technology for civil engineering applications to Hydrolog (French SME), supported by the European Community and the french ministry of Industry. In order to check the reliability and user-friendliness of this instrumentation, eleven spectrally-multiplexed Bragg grating-based extensometers, four FBG temperature sensors and an acquisition unit have been installed into the Saint-Jean bridge in Bordeaux, France with the help of the Infrastructure Regional Direction (DRE-Aquitaine) and the Bordeaux Authority (Communaute Urbaine de Bordeaux). A standardized loading of the bridge has been performed on October 29, 1001, with the purpose of correlating its mechanical reaction to loading conditions. Moreover, the equipment has been operating for one year to take into account the winter-summer cycle.
A new kind of instrumentation based on Optical Fiber Bragg grating sensors is proposed for the main relevant monitoring needs in the electric power industry. The challenging metrological properties of these components are presented and their good resistance to (gamma) -ray irradiations experimentally proved.
Recent developments of stability control in mines, essentially based on Ge-doped Fibre Bragg Gratings
(FBG) are reported including results about the different aspects of the system : accurate characterisations of FBG,
sensor network topology and multiplexing method, user interface design and sensor packaging.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.