Abstract:

Triggered seismicity remains one of the main geomechanics hazards that affect safety in deep mining. Mobilization or propagation of existing faults can potentially release large amounts of seismic energy that in turn may trigger rockbursts and falls of ground, threatening worker safety and generating production delays. Current modeling approaches, typically based on stress analyses, do not fully succeed in capturing such seismically triggered mechanisms as the main seismic event location may be beyond the volume of rock affected by the mining induced stress perturbation. However, the displacement field generated by the excavation process may explain the triggering of far-field seismicity. Deeper understanding of the mining-induced deformation field is the motivation for the development of mine-scale deformation monitoring techniques. Innovative deformation sensors developed for structural monitoring based on fibre optic technology allows distributed measurement of strain at high spatial sampling rates over large distances. This paper presents the results of the testing of one of these systems in an active mining context. The system selected is based on Brillouin Optical Time Domain Analyses (BOTDA) and allows for a spatial resolution of 10 cm. It has been tested in the laboratory and installed in five boreholes piercing through an actively mined, 25 m thick, 1000 m deep, sill pillar. Benchmarking of the system against extensometer results was successful in a qualitative manner. The high spatial resolution of the fibre optic system brings valuable additional insights to rock mass deformation processes.

1 INTRODUCTION

Currently, the single monitoring systems with high spatial and temporal resolution that are deployed in deep underground mines are seismicity and microseismicity monitoring systems. However, much of the rock mass deformation and failure process occurs occurs without generating measurable micro-seismicity. Thus, microseismic emissions can account for only a tiny portion of the total energy balance (Das and Zoback, 2011).

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