Research on wall cutting using a mixed hydraulic-directed blasting method in mining technology without leaving protective pillars

Abstract

Controlling the rock mass's state to relieve mine pressure on the longitudinal haulage roadway in the longwall pressure zone is the most important and complex technological stage in the combination of support and maintenance solutions for reusing the longitudinal haulage roadway under non-pillar mining schemes. Directional roof-cutting blasting has been widely applied in China and the Russian Federation. Due to the the wide variability in physico-mechanical properties and structural characteristics of roof strata, it is difficult to form an ideal fracture surface (weakly connected surface) that allows the roof to cave and break as expected. In practice, combined methods are commonly employed: combining the method of concentrated blasting to cut the rock face with the method of blasting to break up the rock mass;  combining the method of directional hydraulic blasting with the method of blasting to break up the rock mass. These approaches result in a very large volume of drilling and blasting work, especially in the case of mining thick seams according to the longwall mining scheme - lowering the roof to recover coal and the rock face is of a stable, non-collapsible type. Based on theoretical research and practical application of methods to weaken the rock mass, the authors propose a technology for roof cutting using a combined hydraulic-directional blasting method applied to the conditions of mining thick seams and some experimental results of the technology at the IV-9-17 longwall haulage roadway of Ha Long Coal Company.