Efficiency and seismic safety of constructing underground structures in complex rock masses

Abstract

Purpose. To develop new resource-saving method of underground construction and evaluate how effective it is, to set thresholds for safe seismic ground vibrations which accompany explosions during breaking in mine workings. Methodology. The work used method of analysing mining and geological conditions of workings, field surveys of rock conditions in face, experiments are conducted on rock samples taken from blasting sites, more detailed data are obtained on rock properties, type and direction of development of crack systems along the workings cross-section by funneling method and approved research methods in accordance with current State Standards. Findings. Research has been carried out to determine main features of physical and mechanical properties of rocks, fracture and tectonic structure of rock mass and development of fracture systems. According to the results of ejection funnel parameters, the anisotropy coefficient was calculated, and according to data on identification of crack systems and their density, fracture coefficient was calculated. The experimental data obtained were used to adjust rational distances between contour boreholes and along the entire cross-section of working face. Based on corrected drilling and blasting operations (DBO), experimental explosions were carried out in workings. It was established that the borehole utilisation rate (BUR) was 0.95–0.97, uniformity of rock mass crushing was achieved, and explosive material consumption was reduced by 10–15 %. Instrumental measurements of explosion impact in workings proved seismic ground vibrations at protected facilities amounted to 0.4 cm/s with a duration of 0.05 s, which did not exceed the State Standard. Originality. Optimal DBO parameters are substantiated based on changes in numerical parameters of anisotropy and fracture coefficient, as well as radius of fracture zone along the cross-section of working face. The idea of forming a shielding zone along the contour of workings with explosive charges having an elongated symmetrical cut was confirmed and technically implemented. Practical value. Laboratory and field research results are fundamental for designing borehole layouts along workings and refer to major initial data used to justify design parameters of blasting chart.