Distributed acoustic sensing in soil for infrastructure monitoring

Fibre-optic distributed acoustic Sensing (DAS) provide information on vibration response comparable with geophones and seismometers and may become widely used for infrastructure monitoring. DAS can be used to monitor earthquake activity, carbon dioxide sequestration, pipelines and roadway/railway subgrade integrity. 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 field study in which DAS 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 programme indicate that portions of the array in sand, gravel and silty sand had a good response with comparable SNR. A newer portion of the array showed ∼5 dB 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.