Aiming to preserve integrity of rubies extracted with from primary deposits using room-and-pillar method with hydraulic fracturing, the authors discuss scenarios of moderate blasting with decoupled explosive charges meant to keep unbroken blocks preconditioned by fracking.
Hydraulic fracturing process splits rock mass into blocks and destresses it. To break-off preconditioned blocks, it is required to carry out very moderate, tender blasting at the bottom of a central blasthole or additionally drilled blastholes so that blast wave widens hydorfractures and throws blocks at a certain distance on the floor of a panel or roadway. It is recommended to use decoupled explosive charges. In this case, the seismic effect of blasting on rock mass is reduced owing to incomplete fill of blasthole through the length and cross-section, as well as due to lower density of explosive; thus, the direct connection between explosive charge and rock mass is broken.
Ordinary blasting, especially with high power explosives, creates damaged rock zones that are patterns of micro- to macroscopic cracks coupled with radial spalling. Noncompliance with the design blasting pattern, use of high power explosive, neglect of controlled perimeter blasting and poor knowledge on physico-mechanical properties of rocks result in that excavations and panels suffer from too large cross-section after blasting and blocks preconditioned by hydraulic fracturing are damaged.
It is found that moderate blasting with decoupled charges minimizes aggravating effect on fracking-preconditioned blocks in room-and-pillar mining and mitigates disturbance of surrounding rock mass using the following engineering solutions: reduced energy of explosion per meter of blasthole; reduced number of blastholes to be charged; incomplete fill of blastholes; additional hole drilling inside the blast pattern to implement transverse hydraulic fracturing and moderate explosion; delayed detonation of explosive charges to produce free surface and maximum block separation angle.
The experimental investigation of moderate blasting with different density explosives in mines has shown that the highest quality is achieved with encapsulated decoupled explosive charges and with a compound explosive composed of Igdanite and polystyrene granules, for example, at a mix ratio 50/50.

Issue number: 3
Year: 2016
UDK: 622.831; 622.2; 622.235
Authors: Barnov N. G., Eremenko V. A., Kondratenko A. S.

About authors: Barnov N.G., Candidate of Geological and Mineralogical Sciences, Researcher, e-mail:, Institute of Mineralogy, Geochemistry and Crystal Chemistry of Rare Elements, 121357, Moscow, Russia, Eremenko V.A., Doctor of Technical Sciences, Leading Researcher, e-mail:, Institute of Problems of Comprehensive Exploitation of Mineral Resources of Russian Academy of Sciences, 111020, Moscow, Russia, Kondratenko A.S., Candidate of Technical Sciences, Acting Director, Chinakal Institute of Mining of Siberian Branch of Russian Academy of Sciences, 630091, Novosibirsk, Russia.

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