Activities About Applying Distributed Optical Fiber Sensors to Analyze the Internal Structure of Road Pavements

Structural health monitoring (SHM) using distributed optical fiber sensors (DOFS) is actively conducted in civil engineering and aviation fields. One such activity is establishing road infrastructure that supports mobility services by embedding DOFS in the pavement to capture vibrations from moving entities such as pedestrians and vehicles. Road pavements consist of multiple layers, including asphalt and gravel layers, with different physical properties, such as elastic modulus and density for each layer. While it is easy to evaluate amplitude values and surface temperature using sensors quantitatively, it is challenging to install sensors within the pavement, and few activities allow for quantitative evaluations. On the other hand, DOFS exhibit excellent workability, allowing them to be easily embedded within the internal structure of road pavements, which holds the potential for understanding the internal structure through measurement. Distributed acoustic sensing (DAS) is one measurement technology that uses optical fibers. It can measure the elongation strain applied to the optical fiber over its entire length at a high sampling rate of up to several kHz. Verifying the quantitative nature of DAS is crucial for enhancing the detection accuracy of moving entities. The authors focused on the Falling weight deflectometer (FWD) test, which is commonly used to determine the elastic modulus of road pavements. They comprehensively evaluated the measurement values obtained from the FWD test in conjunction with those from DAS.