Authors: Akutagawa, S; Machijima, Y; Katayama, T

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DOI https://doi.org/10.36487/ACG_rep/1508_29_Akutagawa

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Akutagawa, S, Machijima, Y & Katayama, T 2015, 'A new method for interpreting changes in arbitrary engineering quantities by using optic fibre', in PM Dight (ed.), Proceedings of the Ninth Symposium on Field Measurements in Geomechanics, Australian Centre for Geomechanics, Perth, pp. 439-451, https://doi.org/10.36487/ACG_rep/1508_29_Akutagawa

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Abstract:
A new monitoring method is proposed, which is designed for reading and interpreting changes in general engineering quantities such as deformation, subtle movement of soil particles, alteration of underground water level etc. The key feature in the method lies in the use of plastic optic fibre used to read changes in general engineering quantities occurring in geo-materials, by measuring light intensity affected by these phenomena. In this method, two plastic optical fibres, both having diameter of 1 mm, are used to read local disturbance or deformation at a point in granular material, such as sand, soil, or broken rocks. As light is sent into the first fibre and reaches its end, it leaves the fibre and hits surfaces of nearby particles. Part of the reflected light then gets into the second fibre, which can be digitally recorded by using photo diode. The paper introduces the fundamental mechanism of how the system works, shows several examples in which the proposed method is tested to interpret turbidity of muddy water, collapse behaviour of a model slope, liquefaction and so on. The results show the use of light for reading various behaviours is promising as a new monitoring scheme for rock engineering projects.

References:
Akutagawa, S & Takahashi, A 2014, Patent no. 5607185: Sensor device to detect arbitrary changes occurring in natural and artificial structures, Japan.
Akutagawa, S, Nishio, A, Matsumoto, Y, Takahashi, A & Machijima, Y 2014, ‘A new method for reading local deformation of granular material by using light’, Proceedings of the 48th US Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association, Minneapolis, 6 p.
Hill, KO, Fujii, Y, Johnson, DC & Kawasaki, BS 1978, ‘Photosensitivity in optical fiber waveguides: application to reflection filter fabrication’, Applied Physics Letters, vol. 32, no. 10, pp. 647-649.
Matsumoto, Y 2014, ‘Development of a monitoring method for infrastructure by measuring change in light intensity’ Master’s thesis, Kobe University.
Meltz, G, Morey, WW & Glenn, WH 1989, ‘Formation of Bragg gratings in optical fibres by a transverse holographic method’, Optics Letters, vol. 14, no. 15, pp. 823-825.




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