Applications of Optical Fiber Sensors in Geotechnical Engineering: Laboratory Studies and Field Implementation at the Acropolis of Athens.

The current study investigates the feasibility and performance of Fiber Bragg Grating (FBG) optical sensors in geotechnical engineering applications, aiming to demonstrate their broader applicability across different scales, from controlled laboratory experiments to real-world field implementations. More specifically, the research evaluates the sensors' ability to monitor key parameters-strain, temperature, and acceleration-under diverse loading conditions, including static, dynamic, seismic, and centrifuge loads. Within this framework, laboratory experiments were conducted using the one-degree-of-freedom shaking table at the National Technical University of Athens to assess sensor performance during seismic loading. These tests provided insights into the behavior of geotechnical physical models under earthquake conditions and the reliability of FBG sensors in capturing dynamic responses. Additional testing was performed using the drum centrifuge at ETH Zurich, where physical models experienced gravitational accelerations up to 100 g, including impact loads. The sensors successfully captured the loading conditions, reflecting the anticipated model behavior. In the field, optical fibers were installed on the Perimeter Wall (Circuit Wall) of the Acropolis of Athens to monitor strain, temperature, and acceleration in real-time. Despite the challenges posed by the archaeological site's constraints, the system gathered data over two years, offering insights into the structural behavior of this historic monument under environmental and loading variations. The Acropolis application serves as a key field example, illustrating the use of these sensors in a complex and historically significant site. Finally, the study details the test setups, sensor types, and data acquisition techniques, while addressing technical challenges and solutions. The results demonstrate the effectiveness of FBG sensors in geotechnical applications and highlight their potential for future projects, emphasizing their value as tools for monitoring structural integrity and advancing geotechnical engineering.