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Distributed Acoustic Sensing in Soil for Infrastructure Monitoring SNR Evaluation

Fibre optic Distributed Acoustic Sensing (DAS) systems provide vibration response information comparable to accelerometers, geophones, and seismometers and may become widely used for infrastructure monitoring.  DAS can be used to monitor earthquake activity, carbon sequestration, pipelines, and roadway/railway subgrade integrity, however little is known about the effect of soil type and burial method on DAS response. The objective of this paper is to present the results of a seven-month field study in which a DAS system was installed in different soil types (silty sand, clean sand, gravel, and a flowable fill) adjacent to an existing, decade-old DAS array. Impact tests were performed to evaluate DAS response in the different soil types and a portion of DAS array installed a decade prior. Signal-to-Noise Ratio (SNR) was used to compare performance of DAS response. Results of the monitoring program indicate that portions of the array in sand, gravel, and silty sand had good response with comparable SNR. A newer portion of array performed approximately five decibels better than the decade-old portion of DAS array, both in silty sand, with the old portion still performing well. These results may help build confidence with the geotechnical community regarding the longevity performance of DAS for infrastructure vibration monitoring.