Evaluating Dark Fiber Distributed Acoustic and Strain Sensing for Shallow Ground Movement Monitoring: A Field Trial

Fiber-optic distributed acoustic sensing (DAS) and distributed strain sensing (DSS) using dark telecom fibers enables low-cost monitoring of ground movements. However, the applicability of these methods for localized shallow failures using buried telecom cables requires evaluation. We assessed DAS and DSS performance using a conduit-installed dark fiber subjected to simulated shallow deformations and rockfalls. Brillouin optical time-domain reflectometry recorded DSS with and without events, showing negligible temperature influence. Once residual fiber slack dissipated, conduit-protected dark fiber responded to induced lateral strains. DAS detected rockfalls down to 25 Hz with amplitudes exceeding background noise by 2 orders, correlating with block mass. Preliminary results suggest dark fiber DAS can detect dynamic small-scale rockfalls. DSS provides quantitative strains immobilized to temperature once initial slack is taken up. Combined DAS-DSS may therefore monitor different timescale shallow movements. With development, such distributed sensing utilizing buried telecom infrastructure could enable low-cost near-surface failure monitoring. Further field validation is needed.