Long-hole destress blasting for rockburst control during deep underground coal mining.

Modern longwall mining technology was selected for the extraction of seam 504 at the Lazy colliery in the Ostrava-Karvina coalfield, Upper Silesia coal basin, Czech Republic. The seam is located at a cover depth of about 700 m and is 3.1-5 m thick. Two overlying seams were mined at average heights of 58 and 75 m from the planned working horizon of seam 504. The proposed longwall panel was adversely located below the goaf edges of the workings in the overlying extracted seams. Analysis of the inter-burden rock mass in the coal seams showed the presence of strong, massive strata consisting of sandstones and conglomerates with uniaxial compressive strength values of 70-120 MPa. Laboratory tests on a coal sample showed a high elastic deformation/total deformation ratio, indicating that the seam was prone to bursting/bumping. A de-stress design was adopted involving longhole drilling and blasting to fracture in advance the competent strata from both gateroads. The efficiency of the de-stress blasting at different mining stages was evaluated in relation to the seismic effect, calculated using seismic monitoring data and the weight of the charged explosive. Systematic adoption of de-stress blasting enabled the total 300 m length of the panel to be extracted without the occurrence of bumps or outbursts.
Modern longwall mining technology was selected for the extraction of seam 504 at the Lazy colliery in the Ostrava-Karvina coalfield, Upper Silesia coal basin, Czech Republic. The seam is located at a cover depth of about 700 m and is 3.1-5 m thick. Two overlying seams were mined at average heights of 58 and 75 m from the planned working horizon of seam 504. The proposed longwall panel was adversely located below the goaf edges of the workings in the overlying extracted seams. Analysis of the inter-burden rock mass in the coal seams showed the presence of strong, massive strata consisting of sandstones and conglomerates with uniaxial compressive strength values of 70-120 MPa. Laboratory tests on a coal sample showed a high elastic deformation/total deformation ratio, indicating that the seam was prone to bursting/bumping. A de-stress design was adopted involving longhole drilling and blasting to fracture in advance the competent strata from both gateroads. The efficiency of the de-stress blasting at different mining stages was evaluated in relation to the seismic effect, calculated using seismic monitoring data and the weight of the charged explosive. Systematic adoption of de-stress blasting enabled the total 300 m length of the panel to be extracted without the occurrence of bumps or outbursts.