Numerical study of grout–rock mass interaction effect on distributed optical fibre sensor measurements

Madjdabadi, Behrad; Valley, Benoît; Dusseault, Maurice B.; Kaiser, Peter K.

doi:10.36487/acg_rep/1410_31_madjdabadi

Cited by 2 publications

(4 citation statements)

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“…Alternatively, a "strain free" cable is somehow decoupled from the system of interest and can be co-located with a coupled cable and connected in series. In our case we had access to neither, but we make the assumption that the temperature change within our testbed is negligible with respect to the changes in Brillouin shifts being measured (Hartog, 2017;Madjdabadi et al, 2014Madjdabadi et al, , 2016. We acknowledge that this assumption is likely not strictly true due to ambient changes in gallery air temperature and temperature changes related to grout curing.…”

Section: 𝜕𝜕𝜕𝜕 and 𝐴𝐴 𝜕𝜕𝜕𝜕 𝐵𝐵mentioning

confidence: 99%

The Effect of Fault Architecture on Slip Behavior in Shale Revealed by Distributed Fiber Optic Strain Sensing

et al. 2022

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We use Distributed Strain Sensing (DSS) through Brillouin scattering measurements to characterize the reactivation of a fault zone in shale (Opalinus clay), caused by the excavation of a gallery at ∼400 m depth in the Mont Terri Underground Laboratory (Switzerland). DSS fibers are cemented behind casing in six boreholes cross‐cutting the fault zone. We compare the DSS data with co‐located measurements of displacement from a chain potentiometer and a three‐dimensional displacement sensor (SIMFIP). DSS proves to be able to detect in‐ and off‐fault strain variations induced by the gallery excavated 30–50 m away. The total permanent displacement of the fault is ∼200 microns at rates up to 1.5 nm/s. DSS is sensitive to longitudinal and shear strain with measurements showing that fault shear is concentrated at the top and bottom interfaces of the fault zone with little deformation within the fault zone itself. Such a localized pattern of strain relates to the architecture of the fault that is characterized by a thick “layer” including an anastomosing network of polished surfaces where clay‐rich rock splits into progressively smaller flakes conferring the entire zone very little cohesion and friction (weak zone), and favoring slipping at the edges of the “layer”. Overall, DSS shows that slow slip may activate everywhere there is a weak fault within a shale series. Thus, our work demonstrates the importance of shear strain on faults caused by remote loading, highlighting the utility of DSS systems to detect and quantify these effects at large reservoir scales.

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Section: 𝜕𝜕𝜕𝜕 and 𝐴𝐴 𝜕𝜕𝜕𝜕 𝐵𝐵mentioning

confidence: 99%

The Effect of Fault Architecture on Slip Behavior in Shale Revealed by Distributed Fiber Optic Strain Sensing

et al. 2022

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“…This method has been proposed by several researchers in the distributed fiber optic sensing space, namely Madjdabadi (2016aMadjdabadi ( , 2016bMadjdabadi ( , 2012 [7,20,21], as well as Tang (2015), who proposed a long gauge distributed fiber sensor for monitoring in concrete beams [22]. Most recently an interval gauged optical fiber was proposed by Han (2021) [18].…”

Section: Hybrid Fiber Optic Cable For Strain Sensing In Brittle Mediamentioning

confidence: 99%

“…Laboratory scale research has been conducted by Madjabadi (2012Madjabadi ( , 2016aMadjabadi ( , 2016b towards the development of a novel fiber optic cable design for accurate strain measurements in boreholes drilled in rock and filled with brittle media. The experiments compared the performance of various optical fiber installation techniques (point-fixation, overall bonded, and micro-anchored with intentionally de-bonded areas between anchor points) for strain measurement along progressively widening cracks in a concrete beam [7,20,21]. The microanchored cable with intentionally de-bonded areas proved to be the best design; however, the de-bonding was achieved through the application of a gel to the outside of the cable and had little commercial viability.…”

Section: Introductionmentioning

confidence: 99%

“…The use of interval bonding, such as the anchored and intentionally de-bonded cable proposed by [7,20,21], permits the easy interpretation of DOFS data, in that the strain can be directly equated to displacement if the interval selected is sufficiently greater than the spatial resolution of the interrogation system, and the bonding of the optical fiber to the installation media is sufficiently strong such that slippage does not occur. It is evident that there is a need for a commercially viable and practically feasible sensing cable that can combine the advantages of point-fixation installations (minimal slippage, known gauge length, easy interpretation) with the straightforward installation process of overall bonded cables (cemented in place in boreholes or large structures).…”

Section: Introductionmentioning

confidence: 99%

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Hybrid Fiber Optic Cable for Strain Profiling and Crack Growth Measurement in Rock, Cement, and Brittle Installation Media

Nowak

Sherizadeh

Esmaeelpour

et al. 2022

Sensors

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Brillouin scattering-based distributed fiber optic sensing (DFOS) technologies such as Brillouin optical time domain reflectometry (BOTDR) and Brillouin optical time domain analysis (BOTDA) have broad applicability for the long term and real-time monitoring of large concrete structures, underground mine excavations, pit slopes, and deep subsurface wellbores. When installed in brittle media, however, the meter scale spatial resolution of the BOTDR/A technology prohibits the detection or measurement of highly localized deformations, such as those which form at or along cracks, faults, and other discontinuities. This work presents a novel hybrid fiber optic cable with the ability to self-anchor to any brittle installation media without the need for manual installation along fixed interval points. Laboratory scale testing demonstrates the ability of the hybrid fiber optic cable to measure strains across highly localized deformation zones in both tension and shear. In addition, results show the applicability of the developed technology for strain monitoring in high displacement environments. Linear relationships are proposed for use in estimating the displacement magnitude along discontinuities in brittle media from strain signals collected from the hybrid fiber optic cable. The hybrid fiber optic cable has broad potential applications, such as geomechanical monitoring in underground mines, surface pits, large civil infrastructure projects, and deep subsurface wellbores. The benefits of fiber optic sensing, such as the intrinsic safety of the sensors, the long sensing range, and real time capabilities make this a compelling technique for long term structural health monitoring (SHM) in a wide range of industrial and civil applications.

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Numerical study of grout–rock mass interaction effect on distributed optical fibre sensor measurements

Cited by 2 publications

References 0 publications

The Effect of Fault Architecture on Slip Behavior in Shale Revealed by Distributed Fiber Optic Strain Sensing

The Effect of Fault Architecture on Slip Behavior in Shale Revealed by Distributed Fiber Optic Strain Sensing

Hybrid Fiber Optic Cable for Strain Profiling and Crack Growth Measurement in Rock, Cement, and Brittle Installation Media

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