Engineering methodology for operative assessment of seismic blast impact in the boundary rock mass in open pits

In order to assess the seismic impact of large-scale blasts on the rock mass immediately adjacent to the blasted block, measurements of the ground displacement rate in the near zone of the blast action were carried out in various sections of the Zhelezny open pit mine of the Kovdorsky GOK JSC. According to the degree of the the rock mass response to dynamic impacts, the open pit was zoned depth-wise. Three areas of seismicity were identified, for which empirical dependences of the change in the displacement rate on the reduced distance and the corresponding coefficients of seismicity and attenuation were obtained. The sizes of the induced fracture zone were calculated using these dependences in relation to the permissible displacement rate. The average size of the jointed rocks increases with the depth of the open pit: it starts sharply (from 0.22 to 1.19 m) within the interval of 0-150 m from the day surface, then continues gradually (from 1.19 to 1.4 m) down to the depth of 450 m, and deeper stabilizes at the level of 1.4-1.5 m, which gives the difference in the size of the induced fracture zones. An engineering methodology was developed for operational assessment of the seismic blast impact on the boundary rock mass during blasting operations in open pits to calculate the width of the cutter break zones, fracturing into the rear part of the rock mass and zones of induced fracturing. Calculations at the design stage allow selecting blasting parameters that minimize the seismic impact on the boundary rock mass. A software program has been developed for operative calculation of the fracture boundaries position in the rear part of the rock massif during borehole blasts. The obtained calculated values are in good conformity with the previously obtained modeling and application data.