The Application of Fibre Optic Sensor Technology in the Integrity Testing of Deep Foundations-Paper

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The paper presents CemOptics, a distributed fibre-optic sensing system developed for thermal integrity profiling (TIP) of deep concrete foundations. Unlike systems using individual embedded sensors, the fibre itself continuously measures temperature along its length. Cables are attached to reinforcement cages and connected to an analyser, allowing multiple foundation elements to be monitored.<br /><br />Temperature profiles reveal variations in concrete hydration that may indicate defects. The authors describe an observational analysis approach: compare temperature changes at different depths and locations, identify unusual deviations, and assess them alongside construction records and ground conditions. Tests on known defects found they were generally most visible near, or shortly before, peak concrete temperature—often when temperatures reached 60–90% of that peak. Monitoring should begin after concreting and continue through peak temperature; an initial period of at least 48 hours is often needed to establish the appropriate assessment window.<br /><br />CemOptics can also record temperatures during construction. Measurements from a diaphragm wall panel showed that cooler concrete delivered after a work delay was not displaced by warmer concrete, but was overlain as fresh concrete flowed upward from the tremie. Such observations may help explain how construction practices contribute to defects.<br /><br />The system was deployed extensively at Battersea Junction Station, monitoring 116 diaphragm-wall panels and 74 bearing piles using more than 50 km of fibre. It offered safety, productivity and cost advantages over conventional testing, and could identify cover-zone information not detected by cross-hole sonic logging alone. The authors conclude that CemOptics is a practical method for assessing foundation integrity and gaining insight into construction processes, with further data expected to improve interpretation and reliability.

Keywords

CemOptics

distributed fibre-optic sensing

thermal integrity profiling

deep concrete foundations

concrete hydration

defect detection

diaphragm wall

bearing piles

temperature monitoring

construction analysis