Download Możliwości identyfikacji stref osłabienia w strukturze złoża rud

This work concerns the identification of weak zones in the structure of a rock
mass endangered by outburst of gases and rocks in the Rudna copper ore mine at
greater depths (approximately 1200 m). A special project has been undertaken for
the recognition of that threat in the wake of an outburst in the mine in 2009. No
similar phenomena have been previously recorded.
The research described in this paper was carried out in the new part of the
deposit prepared for mining. Geophysical methods were mainly used: seismic
tomography and borehole ground penetrating radar (BGPR), along with particular
identifications using geological engineering methods.
In the researched area, Permian layers of sandstone and shale clay and of
Zechstein dolomite and anhydrite occur in the copper ore deposit. The rock layers
are characterized by variable thickness and intensity of mineralization, varying
internal structure, and local fracturing containing different gases and water. It is
assumed that accumulation of gases occurs in the tectonically fractured dolomite.
The study was focused on the recognition of the structure and properties of
the dolomite layer lying directly within the roof of excavations. The first tests were
performed with seismic tomography for the recognition of anomalous changes in the
elastic properties of the rock mass. The results of these studies were used to design
a control borehole for a detailed geological engineering assessment and BGPR
surveys with 100MHz antennas.
Seismic tomography enabled the identification of changes in P-wave and Swave velocity, the Vp/Vs ratio, dynamic Poisson's ratio and dynamic Young's
modulus. It was clear that seismic anomalies required verification by other methods.
The BGPR survey was performed in a specially designed borehole, passing
through the selected seismic anomalies. While the borehole was being drilled, the
outflow of gases was identified, with varying amounts of CH4, O2, CO, and H2S
detected, as well as water outflow. The results of BGPR confirmed the location of a
reservoir of water and gases, about 30 m in length, found in layer of dolomite. The
direct cause of the BGPR anomaly was assumed to be intensive fracturing, a greater
content of clay material in the dolomite, and the presence of water in the fractured
zone. The BGPR image was correlated with information on lithology, fracturing based
on the RQD index and additional information acquired during drilling about water and
gases surveys and other symptoms.
The achieved results also showed a very strong correlation between the
location of the zone containing gases and water and the anomalous S-wave velocity
and field of dynamic Young’s modulus, and to a lesser extent other seismic
parameters.
It was found that the other measured seismic anomalies may be of the same
nature as those identified in the control borehole and accordingly will require the
implementation of detailed identification.
1
The performed tests have also shown the usefulness of geophysical methods
to identify geodynamic hazards under the geological and mining conditions of the
copper ore deposit in the Rudna mine.
2