Distributed Optic Fiber Sensors for Subsurface Concrete Structure Monitoring-Paper

Paper

Pdf Summary

The paper evaluates distributed optical fiber sensing (DFOS) for monitoring the construction and integrity of buried reinforced-concrete structures. Unlike conventional point sensors, DFOS measures temperature and strain continuously along a fiber, providing real-time profiles over substantial depths. Raman backscatter is used for temperature measurement, while Brillouin backscatter provides information on both temperature and strain.<br /><br />The technology was applied to two projects: a 50 m-deep diaphragm wall at a subway station in Montfermeil, France, and a 40 m-deep, 1.2 m-diameter test pile at London’s Old Oak Common station. Fiber cables were attached to reinforcement cages in loops and connected to optical interrogators. The diaphragm wall monitoring tracked temperature during concrete placement and curing; the pile monitoring recorded temperature during curing and strain during subsequent load tests.<br /><br />In the wall, concrete temperature rose to a maximum of 37.14°C. In the pile, it reached 35.6°C. The pile’s distributed strain measurements captured loading and unloading cycles at several depths, showing that strain decreased with depth as the applied load propagated through the pile. The measurements were consistent with conventional strain-gauge results.<br /><br />The authors conclude that DFOS can provide detailed, continuous monitoring of subsurface concrete during construction and testing, supporting assessment of curing, structural response, and potential defects. The recorded temperatures remained below 40°C, which the authors consider to indicate low risk of delayed ettringite formation in these two cases. Successful deployment depends on careful cable installation, though the process generally adds little disruption to construction.

Keywords

distributed optical fiber sensing

DFOS

buried reinforced-concrete structures

Raman backscatter

Brillouin backscatter

temperature monitoring

strain monitoring

diaphragm wall

test pile

concrete curing