Geomechanical behavior of jointed rock mass in the large-scale blast impact zone

Abstract

The review of literature sources has allowed determining the mechanism of seismic blasts waves in jointed rock mass. The author presents the theoretical formulas for calculating stresses, relative strains and displacement velocities induced in rock mass by large-scale blasts. The formulas take into account the detonation characteristics of explosives, the borehole diameter, the length of explosive charges, the number of simultaneously blasted charges per groups and the factor of explosion energy redistribution to rock throw. Moreover, the formulas include the properties of rocks between the blasting point and a guarded object, and on the exposed surface of a guarded object. The compressive stresses, relative strains and displacement velocities in rocks are calculated from the formulas. The theoretically found change in the displacement velocity versus distance agrees with the field measurement data obtained in an open pit mine of Polyus company. The formulas of stresses and relative strains were used to define seismic impact exerted by large-scale blasts on the barrier of dry dock No. 1. Based on the calculated results, the recommendations are developed on reduction of seismic impact of blasts during dredging in the dock. The research findings are applicable to developing blasting regulations toward reduction in seismic impact of large-scale explosions on exposed surfaces in rock mass, as well as on the ground surface structures and buildings.

Seismically safe parameters of confined blasting in levelling dry dock bottom

“…Seismic safety in confined blasting is a subject of research both in Russian [5][6][7][8][9][10][11][12][13][14][15][16] and abroad [17][18][19][20][21]. These works present the experimental, analytical and theoretical studies, discussions and proofs of reliability or appropriateness of the results.…”

“…PPV of ground vibrations due to BSW toward the nearest wall of the caisson (direction 12) is calculated from the formula [14,16]:…”

“…The calculations of PPV in directions 11-13 from formulas (1)-( 4) assume the following values of the involved parameters: explosive is Nitronit-P, blasting is carried out by single blastholes at the delay intervals of 50 ms, the charge length is 4.1 m; D = 3×10 3 m/s; ρ ch = 600 kg/m 3 ; d 3 = 0.064 m; с = 2.7×10 3 m/s; μ = 0.4; ν = = 0.3; ρ go = 2.35 o ×10 3 kg/m 3 ; с go = 4.7×10 3 m/s; R = 8.5 m; R Δ 1 = = 0.18; Δ 2 = 0.7; Δ 2 =0.12; Ф 1 = 5.7; Ф 2 =750; Ф 3 =462; K 1 = = 1; K 2 K =1; K 3 K =1.63; K 4 K =0.8 [14][15][16]; K 1-4 =1.3. Placement of the numerical values in (1)-direction 12-yields the maximum value of PPV υ 1 (R) = 0.0257 m/s or 25.7 mm/s.…”