Spatial scale analysis on coal mining and strata control technologies

The various spatial scales involving in coal mining and strata control are discussed in this paper,which are from global scale to nanopore in coal.The scale distributions of global coal reserves,coal field,coal mining area and well field,coal working,driving and boring,rock mechanics tests,composition and structures of coal and rock,and composition and structures of support and reinforcement materials are analyzed.The main research contents and methodologies about coal mining and strata control under various scales are introduced.It is also pointed out that the spatial scales on coal mining and strata control are in the limits of 10^-10-10⁷ m,stepping across 17 orders of magnitude.The different research contents and methodologies depend on the different spatial scales.Some rock structures in strata control can only exist on fixed scales.The spatial scales of rock structures formed in roadways and working faces,such as beam,arch,layer and shell,are generally in the limits of 10^-1-10² m.It’s closely related to the formation of rock structures.Different scales are used to study the corresponding problems of rock formation control.for example,water softening and swelling of soft rocks,permeability of coal must be studied from micro scales;macro physical and mechanical properties are sufficient for studies on stress and displacement distributions around a roadway or working face.However,there are still some problems,such as rock fracturing,which should be studied from both macro and micro scales.At present,the multi-scale methodology from macro,meso to micro scales is widely applied in coal mining and strata control.It is important to connect various scales with each other.