FeatureOptical Fiber (1)
Use in Construction Management
A reliable infrastructure with optical-fiber neural networks.
Moving towards an unprecedented infrastructure
Kajima is developing innovative optical-fiber sensing technology that can detect strain, temperature, and vibration in invisible parts of infrastructure with high precision.
Optical fibers, which can sense infrastructure over a wide area in real time, are now being used for safe, high-quality- construction management as well as for efficient maintenance and rapid response according to BCPs.
In the future, infrastructure with a neural network of optical fiber has the potential to provide a new feature of infrastructure, such as the ability to transmit data to infrastructure users on the status of its use.
As “distributed optical-fiber-sensor measurement technology that revolutionizes infrastructure sensing,” this optical-fiber sensing technology has also attracted attention from academic societies; namely, it won the 2021 Technology Development Award from the Japan Society of Civil Engineers.
Caisson (structural foundation)
The behavior of the caisson (box-like structure) during installation
is visualized in a way that enables high-quality construction
that is friendly to the surrounding environment.
When the caisson is being lowered, the strain on its body caused by friction with the ground is monitored with high precision in real time by optical fiber. The ability to monitor distribution of minute strain throughout the caisson’s body in real time provides feedback to construction management, which can thereby ensure the quality of the body and assure stable lowering that does not harm the surrounding environment.
Caisson-construction management system using optical-fiber sensors
Installation of optical-fiber sensor
Successful applications
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- Hanshin Namba Line, Yodogawa Bridge reconstruction project and two other applications
List of published papers
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- X. Taira et al., Strain Distribution Measurement of RC Structure using Optical Fiber during Pneumatic Caisson Installation,
Abstracts of the 75th Annual Meeting of the Japan Society of Civil Engineers, 2020.
- X. Taira et al., Strain Distribution Measurement of RC Structure using Optical Fiber during Pneumatic Caisson Installation,
Tunnels
Optical-fiber sensors are also applied in mountain tunnels
that are dug through rock to provide transportation routes and essential utilities.
During the construction of mountain tunnels, excessive loads can act locally and cause the stability of the tunnel to be compromised. Installing optical fiber in the tunnel steel supports makes it possible to understand the complex behavior of the rock being tunneled in detail. Moreover, optical fiber is inexpensive, so if steel supports with optical fiber attached in advance are permanently on-site, it becomes possible to start measuring deformation quickly in the event of a sudden change in the geology.
Optical fiber installed on a tunnel’s ceiling
Installation of optical fiber on steel support structure
Successful applications
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- Construction of the Chuo Shinkansen Central Alps Tunnel (Sanguchi), etc.
List of published papers
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- X. Miyaishi et al., Continuous Stress Measurement and Analytical Study of Tunnel Steel Supports Using Optical Fibers,
Tunnel Engineering Reports, Vol. 30, I-5, November 2020. - X. Ishii et al., Development of Advanced Displacement Optical-fiber Measurement Technology for Mountain Tunnels,
Abstracts of the 77th Annual Meeting of the Japan Society of Civil Engineers, 2022. - X. Kurokawa et al., Development of a System for Continuous Support Optical-fiber Stress Measurement and Data Visualization in Tunnel Cross Sections,
Abstracts of the 76th Annual Meeting of the Japan Society of Civil Engineers, 2021., etc.
- X. Miyaishi et al., Continuous Stress Measurement and Analytical Study of Tunnel Steel Supports Using Optical Fibers,
Dams
Optical fiber can also be used to understand the behavior of huge dams
and thereby be used as a means to ensure structural integrity.
During the construction of dams, to build a waterproof structure, reliable grouting of the foundation rock is paramount. By using optical-fiber sensors, it is possible to capture the behavior of cracks in the bedrock and the penetration of materials injected during grouting. It thereby becomes possible to install high-quality bedrock efficiently. Moreover, optical fiber has excellent long-term durability and can be used for monitoring during test impoundment after the dam is completed and during maintenance and management.
Demonstration test on curtain grouting
Example of use in treatment work on dam foundation
Monitoring during maintenance
Successful applications
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- Naruse Dam and other dams
List of published papers
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- X. Kobayashi et al., Evaluation of Dam Foundation Grouting by using Optical Fiber,
Abstracts of the 77th Annual Meeting of the Japan Society of Civil Engineers, 2022. - X. Koizumi et al., Advanced Construction Management Methods for Dam Foundation Treatment Work using Optical Fiber,
Abstracts of the 75th Annual Meeting of the Japan Society of Civil Engineers, 2020.
- X. Kobayashi et al., Evaluation of Dam Foundation Grouting by using Optical Fiber,
Bridges
Through tension management using optical-fiber-embedded
pre-stressed concrete (PC) strands, structural integrity is ensured
through more reliable construction management.
We developed a PC strand embedded with optical fiber that makes it possible to visualize the tension distribution along the entire length of the strand. During construction, the optical fiber is used to check that the designed pre-stress is being applied along the entire length of the bridge. This checking enables more-reliable construction management and ensures construction quality.
Measurement of tension via PC strand with built-in optical fiber
A bridge fitted with optical-fiber-embedded PC strands
Successful applications
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- Tsukidate Viaduct, Yoshinogawa Sunrise Bridge, and others
List of published papers
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- X. Okubo et al., Development of PC Tension Distribution Measurement Technology using Optical Fiber Applicable to Tension Management and Maintenance Management,
Journal of the Japan Society of Civil Engineers, E2 (Materials and Concrete Structures), 76(1), 41.54, 2020. - X. Sogabe et al., PC Tension Measurement Technology using Optical Fiber. Concrete Engineering, 56(1), 94-99, 2018.
- X. Okubo et al., Development of PC Tension Distribution Measurement Technology using Optical Fiber Applicable to Tension Management and Maintenance Management,
Measurement of underground displacement
Optical fiber can accurately detect underground displacement
and other changes in real time.
If abnormalities can be promptly detected before they begin to affect the ground surface and infrastructure, construction work can be carried out safely and securely. To detect underground displacement and other changes accurately in real time, we have developed an optical-fiber-sensor cable—called Geo-NewROn—which can measure underground displacement in three dimensions.
Illustration of underground construction in urban areas
Laying conditions at the tunnel shield
List of published papers
-
- X. Nakajima et al., Development of 3D Underground Displacement Measurement Technology using Optical Fiber (Geo-NewROn),
Abstracts of the 77th Annual Meeting of the Japan Society of Civil Engineers, 2022. - X. Nakajima et al., Development of 3D Underground Displacement Measurement Technology using Optical Fiber,
Abstracts of the 76th Annual Meeting of the Japan Society of Civil Engineers, 2021. - X. Nagatani et al., Application Example of Underground Displacement Real-time Visualization Technology in Shield Construction - Results of Underground Displacement Measurement using Optical Fiber -,
Abstracts of the 76th Annual Meeting of the Japan Society of Civil Engineers, 2021.
- X. Nakajima et al., Development of 3D Underground Displacement Measurement Technology using Optical Fiber (Geo-NewROn),
Concrete structures
By monitoring the strain in concrete,
it is possible to detect signs of cracks in concrete structures.
Optical-fiber sensors installed in concrete structures monitor the strain distribution throughout the structure accurately in real time. Since they can capture (in real time) minute changes in strain that occur when cracks appear in concrete structures, they can detect early signs of cracks.
Installation status of optical-fiber sensor
Detection of cracks by using optical-fiber sensors
List of published papers
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- X. Sorimachi et al., Detection of Thermal Cracks in Concrete by using Optical Fibers, Abstracts of the 76th Annual Meeting of the Japan Society of Civil Engineers, 2021.
- X. Kobayashi et al., Remote Real-time Monitoring of Temperature and Strain Measurements using Optical Fibers, Abstracts of the 77th Annual Meeting of the Japan Society of Civil Engineers, 2022.
Introduction to measurement technology
Distributed optical-fiber sensors can even detect
the slightest changes in structures,
even if they occur at an unknown location.
Optical-fiber sensors analyze scattered light that occurs when light propagates through an optical fiber; therefore, they can comprehensively collect strain and temperature information over the entire length of the optical fiber. However, while the Brillouin scattered light that was previously used had a wide measurement range, its accuracy was insufficient, so its range of application was limited. Recently, a high-speed, high-precision measurement technology utilizing Rayleigh scattered light has been practically applied. As a result, it has rapidly expanded the applications range of infrastructure monitoring using optical-fiber sensors.
Features of optical-fiber sensors
Long distance (up to km)/high resolution (up to cm)
Rayleigh measurement is comparable to that of a strain gauge
Overview of optical-fiber measurement system
Scattered light generated in optical fiber
When light is incident on an optical fiber, several types of scattered light are generated. The types with the greatest optical power and next-greatest optical power are respectively Rayleigh scattering and Brillouin scattering.
A property of the scattered light is that it changes in response to strain and temperature in the optical fiber.
By analyzing these changes, optical-fiber sensors can calculate changes in strain and temperature.
*Rayleigh scattering: A scattering phenomenon caused by particles smaller than the wavelength of light
*Brillouin scattering: A scattering phenomenon caused by sound waves in optical fibers
Differences in the properties of Rayleigh-scattered light and Brillouin-scattered light
When strain in an optical fiber varies, the spectrum of both types of scattered light shifts in the frequency-axis direction.
Rayleigh-scattered light forms a finer scattered-light spectrum than that of Brillouin scattered light, so the former can detect a frequency shift even for slight changes in strain.
