Polar Division, Norilsk Nickel, Norilsk, Russia:

E. A. Kubuzov, Head of Mining Department, ggu@tf.nk.nornik.ru
Yu. N. Nagovitsyn, Chief Engineer, Geodynamic Safety Center

VNIMI Institute, Saint-Petersburg, Russia:
A. A. Andreev, Head of Norilsk Sector
G. D. Rukavishnikov, Leading Specialist

The underground mining project for the steeply dipping thin rich copper–nickel ore body (named the Second Southern Lens) included bottom-up slice longwall with cemented backfilling. The lens occurs within the Mayak Mine field of the Norilsk Mining and Metallurgy Company. Since the beginning of mining with the mentioned method, the operations faced problems connected with the instability of development and preparatory drives due to severe jointing of overlying rock mass even more weakened by multiple undermining. Assessment of the effect of undermining on rock mass deformation involved mathematic modeling of rock mass behavior in the course of mining with one, two and three stoping horizons. The modeling and auxiliary research have recovered complete deformation pattern in rock mass, and it has been recommended to adjust the method of mining as a result and to change from the bottom-up to the top-down sequence. This will eliminate negative effect of rock mass undermining on underground stability of excavations owing to replacement of weak rock mass by reinforced cemented backfill of the controllable strength. At the present time, the mine implements the transition to the top-down mining method: the most of the existing excavations at the bottom of the ore body are backfilled with concrete M60; entry ways are driven at the top of the ore body; a potential increase in parameters of the entry ways is discussed.

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