Assessment of Distributed Acoustic Sensing (DAS) performance for geotechnical applications

Distributed Acoustic Sensing (DAS) is a recent technology that acquires acoustic vibrations via fiber optics sensors. The utilization of such technique for near-surface geotechnical applications has great potential, especially for the characterization and verification of artificially stabilized ground. A popular procedure to stabilize the superficial ground (for example, for the preparation of infrastructure subgrade) is the blend of the natural shallower layer with a binder (lime and/or cement). Quality control is required when the binder hardens, and acoustic surveys are an option for non-invasive and non-destructive testing. Relevant parameters to validate the effectiveness of the stabilization procedure are the mechanical properties of the materials. The distribution of shear-wave velocities in the ground is a critical parameter for the geotechnical characterization, since it depends directly on the shear-modulus of the media. The present experiment verifies the applicability of DAS technology in such geotechnical contexts, which can be representative of a wide range of utilizations, spanning, for example, from road and pavement design to building constructions. The discussed test focuses on the spectral content of the acquired signal and on the estimation of the shear-wave distribution, and compares the DAS responses against signals measured during more traditional seismic surveys using standard geophones. Despite the inevitable differences between the datasets collected with the different techniques, all the reconstructed shear-wave velocity profiles effectively identify the stabilized soil layer. Also for this reason, one of the main conclusions is that, for geotechnical characterizations, DAS can be a convenient non-invasive alternative to more standard approaches.