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.

Fiber optic distributed acoustic sensing (DAS) technology can monitor vibrational strain of vast areas with fine spatial resolution at high sampling rates. The fiber optic cable portion of DAS may directly monitor, measure, and map potentially unsafe areas such as thin ice sheets. Once the fiber optic cable is emplaced, DAS can provide “rapid-response” information along the cable’s length through remote sampling. A field campaign was performed to test the sensitivity of DAS to spatial variations within thin ice sheets. A pilot field study was conducted in the northeastern United States in which fiber-optic cable was deployed on the surface of a freshwater pond. Phase velocity transformations were used to analyze the DAS response to strike testing on the thin ice sheet. The study results indicated that the ice sheet was about 5 cm thick generally, tapering to about 3.5 cm within 2 m of the pond’s edge and then disappearing at the margins. After validation of the pilot study’s methodology, a follow-up experiment using DAS to collect on a rapidly deployed, surface-laid cable atop a larger freshwater pond was conducted. Using phase velocity transformations, the ice thickness along the fiber optic cable was estimated to be between 25.5 and 28 cm and confirmed via ice auger measurements along the fiber optic cable. This field campaign demonstrates the feasibility of employing DAS systems to remotely assess spatially variable properties on thin freshwater ice sheets.

Permafrost extent and active layer thickness (ALT) have implications for polar-region infrastructure and communities. Much of the world’s permafrost is rich in ground ice and can become highly unstable during seasonal freeze–thaw cycling. Monitoring these dynamics is critical for quantifying infrastructure risk, informing new construction, and prioritizing essential repairs of existing infrastructure. Fiber optic distributed acoustic sensing (DAS) offers an alternative, providing high-resolution monitoring over large distances. This proof-of-concept study evaluates a surface-deployed DAS cable as a rapid, nondestructive tool for observing seasonal thaw in discontinuous permafrost in Fox, Alaska. During three field campaigns (May 2024, September 2024, and June 2025), a surface laid cable recorded active source sledgehammer strikes. Dispersion curves extracted from the surface wave data were aligned with theoretical curves using a simplified two-layer forward model, representing a seasonally thawed layer overlying hard frozen ground. Based on best fit estimates derived from this model, the active layer thickness was calculated at approximately 0.8 m in May 2024, thickening to 1.9 m in September 2024, and 0.65 m in June 2025. These results demonstrate that surface-deployed DAS can effectively observe changes in permafrost seasonal thaw. This technique could be used prior-to and/or in-addition-to performing more invasive, time-consuming subsurface investigation.

Earthen dam failures of high hazard dams are expected to cause downstream human life loss and economic and environment loss. Of the three most prevalent failure modes for earthen dams, seepage (or piping) failures account for approximately 40 percent. All earthen dams seep and it is not uncommon to observe some seepage on the downstream toe, but the flow rate of uncontrolled seepage should be negligible. In general, seepage occurs through the dam and/or its foundation. The cross section of the dam is designed to force the waterside head (pressure) to drop as the water flows through the cross section to the downstream toe. Uncontrolled or unexpected seepage can promote soil movement (i.e. piping) and cause a pipe or a cavity to develop within the earthen structure which can lead to a complete failure of the embankment. At present there are over 84,000 earthen dams throughout the United States many of which depend on the US Army Corps of Engineers for inspection, monitoring, maintenance, and repair. Recently a multi-method geophysical investigation, was performed at a site where a suspected seep outflow had increased ten-fold, warranting further investigation. Because the seep presented in a historically dry stream channel in the karst bedrock adjacent to the dam abutment there was some question as to whether the origin of the seep was indeed a result of piping or due to a naturally occurring seasonal spring. Electromagnetic induction measurements of terrain conductivity, as well as electrical resistivity tomography and mise-a-la-masse surveys were performed in an attempt to delineate the source water of the seep. The geophysical methods identified potential flow paths from the impoundment to the seep; however, a geochemical analysis of the seep outflow was compared to the same analysis of the impoundment water on the upstream side of the dam and found to be statistically different.