Instability mechanism of overlying strata in shallow interval goaf and structural model of “W-shaped voussoir beam”

Abstract

In order to study the failure mechanism of overlying strata (OS) in shallow insufficient mining areas, with a combination of such research approaches as field investigation, theoretical analysis, similarity simulation, and numerical simulation, this paper has studied the temporal and spatial evolution of the failure mechanism of overlying stratum structure in a shallow-buried interval goaf. The results show that the creep failure of temporary coal pillar (TCP) in the interval goaf is a primary reason for the failure of the basic roof. With the failure of the basic roof, stress arches in the OS of the mining section become unstable, which expands the damage range of the overlying strata. Consequently, adjacent stress arches overlap with each other, forming a ‘trapezoidal—semi-elliptical arch’ collapse shape. Thick soil layers gradually collapse to the ground surface, and the overlying strata collapse as a whole into a trapezoid-like shape. Rotary failure appears in the basic roof of mining section, forming a ‘W-shaped voussoir beam’ hinge structure. In this study, a structural model of ‘W-shaped voussoir beam’ in the OS has been established, and the mechanical characteristics of rock blocks in the basic roof of overlying strata during different mining stages of the interval goaf have been analyzed. Also, with a discrete element UDEC program, this study has performed a simulation to verify the rationality of the ‘W-shaped voussoir beam’ structural model of overlying stratum movement in the shallowly-buried interval mining section.