Mining Institute of Kola Science Center of Russian Academy of Sciences (Apatity, Russia):

Kozyrev S. A., Head of Laboratory, Doctor of Engineering Sciences, e-mail: skozirev@goi.kolasc.net.ru
Fokin V. A., Leading Researcher, Doctor of Engineering Sciences

Despite certain progress in solving of principal scientific-technical problems on seismicity of industrial blasts, mining enterprises majority regularly face questions on development of engineering methods of prediction and management of seismic actions of blasts, aimed at provision for safety of buildings and facilities in blasting region. This problem is urgent for protected buildings and facilities at mines’ industrial sites and adjoining residential areas, located at valleys between mountains or at the mountains foot, on soils with variable thickness of sediments. Instrumental observations for seismic action of bulk blasts on remote distances have shown that intensity of impact on buildings and facilities for given mining-geological conditions doesn’t correspond to known regularities. At the same time, there are observed the unexpected effects, connected to occurrence of different damages of residential buildings. Moreover, damages occurred at such distances from a blast, where they were not predicted according to universally recognized assessment criteria. Many researchers connect these effects with resonant occurrences in buildings. However, regulations don’t consider them at choosing permissible loadings on buildings and facilities. The article presents the results of seismic measurements on open pit bulk blasts impact on buildings and facilities of industrial site and Oleniy Ruchey mine, located at 2 km from the open pit. There are also presented the principal technical solutions and guidelines to seismic safety assurance. Seismic measurements were simultaneously carried out on open pit benches, in zone of seismic waves transfer from hard rock mass to soil sediments, on soils at buildings foundations, and on the first and fifth floors of the most important administrative complex. There was established that soil conditions make a significant influence on intensity of vibrations, its frequency composition and duration, required to be taken into account when selecting permissible displacement velocity for protected facilities. There was revealed that vibrations duration has practically same values on pit benches (distances from 150 to 600 m) and on cliff above an entrance (distances from 1700 to 1900 m). Duration of vibrations is equal to one of blast development at short-delayed blasting and is 1,5–2,0 s. Dominating frequency of vibrations for both measurement points is at the range of 15-40 Hz. Duration of soil vibrations at administrative building foundation and on the first floor is 6–8 sec. Predominating frequencies of vibrations are 3 and 10 Hz. Besides, during transfer of seismic waves from hard rock mass to friable soils, vibrations become more strength, despite of increase of distance. Amplitude of soil vibration at the administrative building foundation exceeds vibrations on the cliff near the entrance under greater part of blasts in 1,5–2,0 times. There was revealed that velocities of displacement and displacements at blasts on the 5th floor are considerably higher than velocities on the first floor and on the building’s foundation soil. Magnitude of the building’s top swinging in relation to its foundation is changed from 2 to 6 times along the displacement of velocity, depending on blasting conditions. It changes from 5 to 8 times along the displacement. Such a considerable magnitude of swinging is related to the fact that in the aspect of a seismic wave, there are vibrations with frequencies close to own frequency of administrative complex. As a result, resonant strengthening of seismic vibrations occurs. Permissible velocities of displacement, as well as recommended and maximum masses of explosives for a stage of delay were determined on the basis of seismic measurements and taking into consideration the duration of vibrations and magnitudes of buildings swinging.

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