• GER-NPM technique induces asymmetric failure patterns in overlying strata. • Roof cutting increases caved zone height and suppresses fractured zone. • A short cantilever beam structure is formed to control strata movement. • Enhanced gangue bulking leads to a 95.83% gob filling ratio. The gob side entry retaining by roof cutting for non-pillar mining (GER-NPM) technique alters the bearing and connectivity conditions of the roadway roof, which causes the collapse characteristics of the overlying strata being different from those in the conventional mining method with coal pillars. To achieve this, an integrated approach combining physical modeling, numerical simulation, and field measurements was implemented to systematically analyze the failure behavior of overlying strata and the developmental characteristics of the caved zone and fractured zone (CZ and FZ) under GER-NPM conditions. A significant asymmetry is observed in the two zones development: the CZ height on the roof-cutting side is 1.32∼1.4 times greater, whereas the FZ height is 0.85∼0.87 times that of the non-roof-cutting side. The resulting filling degree of the gob on the roof-cutting side reaches as high as 95.83%, significantly greater than the 66.37% observed on the non-roof-cutting side. Fundamentally, directional roof cutting severs lateral stress transmission to form a short cantilever beam, promoting fuller caving on the cutting side while restricting the FZ's upward development. Fractal dimension analysis further indicates that the CZ on the roof-cutting side experiences more thorough fragmentation, while the development of the FZ is significantly constrained. By optimizing the stress path and failure structure of the overlying strata, the GER-NPM technique achieves the dual objectives of promoting the active load-bearing capacity of the CZ and suppressing the development of the FZ.
Gao et al. (Fri,) studied this question.
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