Ground Pressure and Methods to Enhance Roof Stability in Mechanized Coal Mining

This paper presents an investigation on the manifestation of ground pressure and rock mass in underground coal mining. By using theoretical analysis, field observation of rock mass stability and field measurement of shield support in a mechanized longwall panel in Vietnam. The study reveals that during normal longwall mining cycles, the ground pressure on shield support increases and decreases cyclically within a period of 4–12 days, equivalent to a face advance of 7.56–22.68 m. Within a ground pressure change cycle, its duration and magnitude vary as the caving span of immediate roof varies. An increase in phase commonly lasts longer than the decrease phase. The coal wall instability is found to strongly relate to the abnormal displacement of shield leg piston. A greater piston displacement than the initially set value may indicate a roof cavity. A greater piston displacement at rear leg than that at front leg may also denote coal wall instability. The short drillhole blasting can be effectively used to some extent in mechanized longwall where coal/rock does not readily cave after shield advance. The findings of the study provide geotechnical engineers with better understanding of ground pressure and rock mass behaviour associated with underground coal mining. More effective controls for safe and productive longwall mining can be accordingly developed.