ABSTRACT

Iron-ore deposits of Siberia are mined at great depths in seismically active regions. The concentration of stresses in separate local parts of rock mass causes dynamic phenomena of different intensity. Dynamic manifestation of rock pressure considerably impedes development, face-entry drivage, and stoping operations in mines as well as leads to heavy expenses for reclamation. Blasting operations are referred to as a technological process that exerts the greatest effect on the state of a rock mass. After technological explosions with a seismic energy of 106-1013 J, the dynamic events in the form of shocks, microshocks, and rockbursts are frequently recorded. The authors have established the connection between blasting and rock pressure manifestations. The velocities of shock and seismic waves in rock mass during large-scale blasts are determined. Preventive actions including the use of explosion energy are developed for safe and effective mining of ore deposits.

The most important means of increase in efficiency of ore extraction is improvement of blasting in underground mining of rockburst-hazardous iron-ore deposits of Siberia. It is a peculiarity of the region, where deposits are located, that it has an increased seismic activity due to deep tectonic processes, high stress level, and type of rocks prone to brittle failure (Fig. I).

Due to the influence exerted by mining operations on seismic activity, local redistributions of stress take place in the rock mass, and the stress field inhomogeneities intensify. This becomes a reason of increased after-effects of earthquakes and dynamic phenomena caused by anthropogenic action on natural environment, Kurlenya (2003).

Investigation of seismic activity in Siberia is aimed at determination of earthquake energies and establishment of connections between the energies of earthquakes and features of tectonics of folded structures, reoccurrence of earthquakes, and character of failure and deformations of rock mass. The Richter rnagnitude 3–8 earthquakes have been observed in the region in question from the 18th century. The latest earthquakes with the magnitude 2–10 have been taking place in the North-West of the Altai-Sayan folded region (Kochurinsk deposit, Tashtagol town) and in Gorny Altai (Kosh-Agach center) from 1988 to 2003.

(Figure in full paper)

Figure 2. Bar chart of distribution of aftershocks of the earthquakes and dynamic phenomena in rock mass during blasting: I - aftershocks of the Kochurinsk earthquake; 2 - aftershocks of thc Altaisk earthquake; 3 - dynamic phenomena; 4 - blasting.

During the earthquakes roads were destroyed, electric mains were broken, soil sagged, cracks formed in the buildings, chimneys were demolished, etc.

Within the same period of time, it was recorded that in rock mass of the deposits, the stress concentration increased. As a consequence of this, rock-tectonic shocks and microbursts occurred in the Tashtagol and Sheregesh deposits. In the epicentral zone of the Kochurinsk earthquakes, there were more than 2000 aftershocks with a seismic energy from 102 to 10101, Kurlenya et al (2001).

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