No abstract

Throughout a mining environment, variations in geotechnical and stress conditions can lead to unplanned rock mass failure. For operations with microseismic monitoring capabilities, seismic event locations and source parameters can often provide significant insight into rock mass failure processes. This paper presents observed variations in the seismic source parameter, apparent stress, during an unplanned rock mass cave in a deep Canadian mine. Over the course of six months, the rock mass cave propagates upwards more than 75 m, at more than 1,000 m depth below surface. Emphasis is placed on identifying zones of relatively high rock mass stress as the cave propagates upwards over time.

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Applying analysis techniques developed for naturally occurring earthquakes to mine seismicity is common practice, however, these methodologies rarely consider the influence of blasting on the dynamic rock mass failure processes observed in mines. Due to the complex nature of bulk orebody extraction at depth, quantifying discrete seismic responses to mining can be challenging. This paper identifies seismic responses to mining by pairing single-link clustering with finite temporal windows bound by mine blasting practices. A methodology is presented to quantify the space-time characteristics of these responses using four Seismic Response Parameters (SRP’s): Distance to Blast, Distance to Centroid, Time After Blast and Time Between Events. Using SRP’s, seismic responses to mining can be quantitatively classified as induced, complex or triggered (with respect to discrete mine blasting). Because these response parameters do not require an extensive and/or triaxial dense sensor array, they are applicable to a variety of underground mining operations. In this work, SRP’s are applied to 189 discrete seismic responses occurring over two months of active mining, and a two week shutdown period, at Agnico Eagle’s LaRonde Mine.

Large-magnitude mining-induced seismic events can occur as a result of local rock mass stress increase. High apparent stress events can be used as a proxy to identify increases in local rock mass stress conditions. This paper proposes a relative apparent stress ratio (ASR) for quantifying apparent stress of a seismic population. Variations in ASR are analysed over time with reference to seismic hazard inferred from the magnitude of seismic events. The proposed ratio is examined through examples of seismic populations from a single deep Canadian mine.