Underground Caverns

OPERATION

We monitor the stability of permanent underground caverns, such as for the storage of nuclear waste, LPG etc., as well as large excavations that house hydro-electric turbines etc.

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 surrounding an underground nuclear waste storage facility. The focus is on monitoring of any induced fracturing as a result of the heat generated by the waste, and also to detect and locate all tunnelling activity near the facility.

COMMUNICATIONS

Multiple netADC units are be linked to a seismic processor via Ethernet cable. The seismic processor communicates with 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.

Alternatively, if fiber optic lines have been installed and a reliable link to surface is possible, then netADC’s can be linked directly to the central computer for continuous streaming of waveforms over Ethernet.

Seismometers on surface can be linked to the central computer via a digital radio (e.g. WiFi) network.

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

SEISMIC SENSORS

In this application, there is sometimes an outer ring of low frequency (1 Hz) geophones, combined with an inner ring of low noise accelerometers. The 1 Hz geophones are installed into vaults on the surface, while the accelerometers would be grouted into boreholes drilled from the underground tunnels. Each netADC data acquisition unit can monitor up to 8 seismic signals, in any combination of uni-, bi- or tri-axial seismic sensors.

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. Spatial and temporal trends may then be detected and analysed using the interpretation package Vantage.