Road deformation monitoring and event detection using asphalt‐embedded distributed acoustic sensing (DAS)

Distributed acoustic sensing (DAS) is a new technology that is being adopted widely in the geophysics and earth science communities to measure seismic signals propagating over tens of kilometers using an optical fiber. DAS uses the technique of phase-coherent optical time domain reflectometry (φ-OTDR) to measure dynamic strain in an optical fiber as small as nε by examining interferences in Rayleigh-backscattered light. This technology is opening a new field of research of examining very small strains in infrastructure that are much smaller than what is currently able to be measured with the commonly used Brillouin-based fiber optic sensing technologies. These small strains can be indicative of infrastructure's performance and use level. In this study, a fiber optic strain sensing cable was embedded into an asphalt concrete test road and spatially distributed dynamic road strain was measured during different types of loading. The study's results demonstrate that φ-OTDR can be used to quantitatively measure strain in roads associated with events as small as a dog walking on the surface. Optical frequency domain reflectometry (OFDR), a widely implemented but less accurate distributed fiber optic strain monitoring technology, was also used along with traditional pavement strain gauges and 3D finite element modeling to validate the φ-OTDR pavement strain measurements. After validation, φ-OTDR strain measurements from various events are presented including a vehicle, pedestrian, runner, cyclist, and finally a dog moving along the road. This study serves to demonstrate the deployment of φ-OTDR to monitor roadway systems.