Caving Mines

OPERATION

A permanent surface and underground installation of seismometers (combination of the seismic sensor and data acquisition unit) communicates with the central computer located on surface for real-time seismic monitoring of the rock mass.

The integrated GPS timing module is used so that recorded seismic data may be integrated with seismic data from another nearby system for information about regional seismic events. Data acquisition units on the surface use also use internal GPS modules to ensure common time with the central computer and thus the underground seismic network.

Communications

Multiple netADC units are be linked to a seismic processor via Ethernet cable. The seismic processor communicates the central computer on surface using DSL protocol. This a cost effective approach as it uses inexpensive 2-core twisted pair copper cable to communicate over long distances with high data rates.

Seismometers on surface can be linked to the central computer via cell modem or digital radio communications, which is cost-effective and more practical than laying direct cable links.

Any number of seismometers can be supported by a IMS seismic network.

Seismic Sensors

The seismic array is carefully designed to monitor the cave initiation and propagation. Sometimes sacrificial sensors are installed ahead of the cave to better monitor the initiation phase. Usually long holes are required to get the full 3D coverage so important for accurate seismic event locations. The IMS Smart Sensors detect their roll inside an inclined borehole, and so the sensor orientation is measured even for long borehole installations. This information can improve location accuracy and is essential for any advanced work on source mechanisms.

Each netADC data acquisition unit can monitor up to 8 seismic signals, in any combination of uni-, bi- or tri-axial seismic sensors. Seismic processors can be customized to handle a scaling number of netADCs, meaning that a single seismic processor can monitor and process seismic channels from multiple netADC’s. Geophones and accelerometers (piezoelectric and Force-Balance) are currently supported.

Seismic Data Processing & Interpretation

The seismograms of every seismic event that triggers multiple stations are transmitted to the central computer. The seismic event is automatically processed and seismic source parameters including the location, time, radiated seismic energy and co-seismic inelastic deformation are automatically calculated. This data is confirmed later by manual processing with the software packages Trace running on either Microsoft Windows or Linux computer. Often this work is done off-site, using IMS’s routine services. 3D ray-tracing can be used to improve seismic event locations, assuming some model of the geological and cave geometry.

Spatial, temporal and source parameter trends may then be detected and analysed using the interpretation package Vantage. A routine analysis and report is often performed by IMS. In particular, analysis of calculated source parameter histories provides information about cave ceiling advancement and changing stress fields as the cave front nears the surface.