NEC, Kajima, and NTT East conducted the world's first successful demonstration experiment for construction vibration detection using existing communication optical fibers

On August 24, NEC, Kajima, and NTT East announced that they had jointly conducted a demonstration experiment in which optical fiber sensing technology was applied using communication optical fibers already co-located on utility poles as vibration sensors, thus marking the world's first successful detection of vibrations in the tunnel excavation work using communication optical fibers. With this measurement technology, construction work can be performed without requiring new sensors, while keeping track of the vibration conditions that occur in the surrounding area as a result of construction work over a wide area in real-time. Based on the results of this demonstration experiment, the three companies would like to continue investigating methods of measuring and visualizing vibration conditions applicable to different construction projects.

When undertaking construction work in urban or residential areas, obtaining the understanding and cooperation of the residents of the surrounding community is crucial. In particular, it is necessary to constantly assess the effects of vibrations caused by construction work to alleviate residents' concerns and be considerate of the surrounding environment. However, the vibrations caused by construction projects vary, and predicting the extent of their impact on particular areas is currently difficult. Additionally, there are limitations associated with the requirement to install multiple vibration meters outside a site for long periods of time for measurement purposes, as well as manual patrol measurements.

To address these challenges, the three companies have been engaged in a proof-of-concept experiment since January 2022, utilizing NTT East's existing communication optical fibers and NEC's and Kajima's optical fiber sensing technology to measure vibrations caused by tunnel excavation work. This experiment aims to continually and comprehensively visualize the extent of the impact of construction vibrations and is scheduled to run until March of next year.

The advantage of this measurement technology is that it does not require the installation of new sensors because it uses communication optical fibers already present throughout the city as vibration sensors. It is possible to simultaneously monitor the vibration distribution over the entire length of the communication optical fiber connected to the sensing device. As no human intervention is required from measurement to visualization, constant monitoring is achievable (24 hours a day, 365 days a year); furthermore, vibrations caused by construction work can be extracted in real-time and mapped on a map.

In the demonstration experiment, a sensing device was attached to the upper end of a communication optical fiber laid in the vicinity of a tunnel excavation site to monitor the transmission of vibrations caused by construction machinery and other vibration sources from the surrounding ground to the general communication optical fiber via utility poles from January 2022 to June 2023.

As a result, detected vibrations were processed via sensing device with communication optical fibers to extract the vibrations caused by construction work, leading to the successful visualization of the impact of vibrations caused by tunnel excavation work on a constant and areal basis.