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Monitoring twin tunnel interaction using distributed optical fiber strain measurements / Hisham Mohamad in Journal of geotechnical and geoenvironmental engineering, Vol. 138 N° 8 (Août 2012) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 138 N° 8 (Août 2012) . - pp. 957–967 Titre : Monitoring twin tunnel interaction using distributed optical fiber strain measurements Type de document : texte imprimé Auteurs : Hisham Mohamad, Auteur ; Kenichi Soga, Auteur ; Peter J. Bennett, Auteur Année de publication : 2012 Article en page(s) : pp. 957–967 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Twin  tunnels  Instrumentation  Weathered  granites  TBM  Fiber  optics  BOTDR  Soil-structure  interactions  Deformation  Ground  settlement Résumé : In this field trial, a new monitoring technique using distributed strain sensing known as Brillouin optical time-domain reflectometry (BOTDR) was introduced to monitor the behavior of bolted-concrete linings of a recently completed tunnel when a second bored tunnel was constructed side by side at a distance less than one tunnel diameter apart. This was done by measuring circumferential strains in 12 rings using optical fiber that was installed using the point-fixing method. The strain distributions around the circumference of the rings show a generally similar profile. Maximum compressive strains measured below the tunnel springline nearest to the excavated tunnel were larger than the maximum tensile strains measured at the tunnel crown, distorting the circular tunnel into an oval/ellipsoid that was about symmetrical to the horizontal axis. Several methods were introduced to compare strain measurements made by BOTDR and diameter changes recorded by tape extensometer. This involves the use of a symmetrical tunnel distortion model and the basic differential equation for a circular arch. The calculated results showed some degree of similarity between the two methods. The analysis highlighted the importance of measuring the axial strain in the tunnel ring and subtracting the axial strain component to calculate the actual deflection of the lining as a result of bending. ISSN : 1090-0241 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000656 [article] Monitoring twin tunnel interaction using distributed optical fiber strain measurements [texte imprimé] / Hisham Mohamad, Auteur ; Kenichi Soga, Auteur ; Peter J. Bennett, Auteur . - 2012 . - pp. 957–967. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 138 N° 8 (Août 2012) . - pp. 957–967 Mots-clés : Twin  tunnels  Instrumentation  Weathered  granites  TBM  Fiber  optics  BOTDR  Soil-structure  interactions  Deformation  Ground  settlement Résumé : In this field trial, a new monitoring technique using distributed strain sensing known as Brillouin optical time-domain reflectometry (BOTDR) was introduced to monitor the behavior of bolted-concrete linings of a recently completed tunnel when a second bored tunnel was constructed side by side at a distance less than one tunnel diameter apart. This was done by measuring circumferential strains in 12 rings using optical fiber that was installed using the point-fixing method. The strain distributions around the circumference of the rings show a generally similar profile. Maximum compressive strains measured below the tunnel springline nearest to the excavated tunnel were larger than the maximum tensile strains measured at the tunnel crown, distorting the circular tunnel into an oval/ellipsoid that was about symmetrical to the horizontal axis. Several methods were introduced to compare strain measurements made by BOTDR and diameter changes recorded by tape extensometer. This involves the use of a symmetrical tunnel distortion model and the basic differential equation for a circular arch. The calculated results showed some degree of similarity between the two methods. The analysis highlighted the importance of measuring the axial strain in the tunnel ring and subtracting the axial strain component to calculate the actual deflection of the lining as a result of bending. ISSN : 1090-0241 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000656

Performance monitoring of a secant-piled wall using distributed fiber optic strain sensing / Hisham Mohamad in Journal of geotechnical and geoenvironmental engineering, Vol. 137 N° 12 (Décembre 2011) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 12 (Décembre 2011) . - pp. 1236-1243 Titre : Performance monitoring of a secant-piled wall using distributed fiber optic strain sensing Type de document : texte imprimé Auteurs : Hisham Mohamad, Auteur ; Kenichi Soga, Auteur ; Adam Pellew, Auteur Année de publication : 2012 Article en page(s) : pp. 1236-1243 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Monitoring  Retaining  wall  Excavation  BOTDR  Sensors  Inclinometer  Piles  Struts  Deformation Résumé : An optical fiber strain-sensing technique, on the basis of Brillouin optical time domain reflectometry (BOTDR), was used to monitor the performance of a secant pile wall subjected to multiple props during construction of an adjacent basement in London. Details of the installation of sensors and data processing are described. Distributed strain profiles were obtained by deriving strain measurements from optical fibers installed on opposite sides of the pile to allow monitoring of both axial and lateral movements along the pile. Methods for analyzing the thermal strain and temperature compensation are also presented. Measurements obtained from the BOTDR were found to be in good agreement with inclinometer data from the adjacent piles. The relative merits of the two different techniques are discussed. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i12/p1236_s1?isAuthorized=no [article] Performance monitoring of a secant-piled wall using distributed fiber optic strain sensing [texte imprimé] / Hisham Mohamad, Auteur ; Kenichi Soga, Auteur ; Adam Pellew, Auteur . - 2012 . - pp. 1236-1243. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 12 (Décembre 2011) . - pp. 1236-1243 Mots-clés : Monitoring  Retaining  wall  Excavation  BOTDR  Sensors  Inclinometer  Piles  Struts  Deformation Résumé : An optical fiber strain-sensing technique, on the basis of Brillouin optical time domain reflectometry (BOTDR), was used to monitor the performance of a secant pile wall subjected to multiple props during construction of an adjacent basement in London. Details of the installation of sensors and data processing are described. Distributed strain profiles were obtained by deriving strain measurements from optical fibers installed on opposite sides of the pile to allow monitoring of both axial and lateral movements along the pile. Methods for analyzing the thermal strain and temperature compensation are also presented. Measurements obtained from the BOTDR were found to be in good agreement with inclinometer data from the adjacent piles. The relative merits of the two different techniques are discussed. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i12/p1236_s1?isAuthorized=no