Furlong, J & Anderson, Z 2022, 'Distributed acoustic sensing/distributed strain sensing technology and its applications for block cave progress monitoring, rock mass preconditioning, and imagining', in Y Potvin (ed.), Caving 2022: Fifth International Conference on Block and Sublevel Caving
, Australian Centre for Geomechanics, Perth, pp. 991-1006, https://doi.org/10.36487/ACG_repo/2205_68
The block cave mining method has grown over the last decade due to its technical and economic benefits. One of the challenges that remains is monitoring the rock mass response, cave progress, and surface subsidence throughout the operation.
Distributed fibre optic sensing (DFOS) is an advanced technology, however, the mining sector remains underserved by this technology that enables an integrated, real-time and high-resolution platform to monitor microseismicity, fracture network propagation, and strain/deformation all using one run of fibre sensing cable.
Distributed acoustic sensing (DAS) interrogators acquire seismic signals along many kilometres of fibre, equivalent to a string of geophones lain end-to-end every metre over its length. DAS enables both active and passive seismic applications and advanced analysis techniques using the same cable and setup. In addition, the DAS system captures low-frequency strain data in real-time indicating fracture network orientation, propagation, and slow strain changes within the rock mass in response to block cave operation.
Because of its wide aperture, DAS systems reduce hypocentre uncertainty compared to conventional geophone arrays. Sampling that is both wider and denser allows for additional precision for seismic imaging techniques such as tomography, ambient noise tomography (ANT), or multichannel analysis of surface waves (MASW). For example, these methods can be used to analyse subsurface velocity variations associated with rock type and structure, or to measure near-surface velocity changes associated with subsidence.
The distributed strain sensing (DSS) interrogator can be integrated into the DAS/fibre system to provide realtime or periodic absolute strain measurement and track rock mass deformation over long periods of time.
This paper provides an overview of DAS/DSS technology in applications such as block caving, preconditioning, and vertical seismic profiling (VSP) seismic surveys. It reviews acquisition design, analysis, and demonstrates the technology’s capabilities and limitations in detecting and processing seismic and strain data.
Keywords: distributed fibre optic sensing, distributed acoustic sensing, distributed temperature sensing, distributed strain sensing, multichannel analysis of surface waves, vertical seismic profiles
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