Impact of Cable Materials and Soil Properties on the Sensitivity of Shaped Fibres for DAS

Summary Deployment of DAS fibres cables on the surface for subsurface imaging has been quite limited, as straight fibres laid horizontally tend to have reduced sensitivity to near-vertical, broadside reflections. Past efforts have explored the use of “SMART DAS” and shaped cables. The sensitivity of shaped cables depends on the wrapping angle, moduli of cable materials and the surrounding rock mass around the cable. Much focus has been on the effect of the fibre’s wrapping, significance of cable materials and soil properties has not been exhaustively investigated. Two different-shaped fibres were deployed for a field test: A 2-millimetres thick plastic jacket cable sinusoidally wrapped was deployed in a trench alongside a thick steel jacket helical cable. Vertical geophones were also co-located with these shaped fibres for data comparison. Preliminary shot records from two shot points along the acquisition layout show that the plastic-jacketed DAS cable exhibits greater sensitivity to orthogonal P-wave strains due to its sinusoidal geometry and flexibility, which enable more efficient strain transfer from the surrounding medium to the fibre compared to steel-jacketed cable. Additionally, the compactness of the cable’s surrounding material further enhances the fibre’s sensitivity to orthogonal strains.