| 摘要 |
PROBLEM TO BE SOLVED: To provide a system for detecting a strain, using optical fibers which can effectively lay the optical fibers in a construction such as tunnels, accurately detect the strain and ensure the safety of strain detection by eliminating the measurement disable time due to troubles of the laid optical fibers, etc. SOLUTION: Six lines of optical fibers are laid on the inner circumferential surface of a tunnel 1 along its axis so that the duplication number of optical fibers 4-1a to 4-1c, 4-2a to 4-2c laid in detecting sections A, B, C on the opposite faces of the tunnel 1 is the same (4 lines), and each optical fiber is selected in time sharing by an optical switch 12 to detect only a specified strain in the tunnel 1 through a stress exerted on each optical fiber, using a strain detector 11.
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