Mechanism and Control of Asymmetric Floor Heave in the Gob-Side Coal Roadway under Mining Pressure in Extra-Thick Coal Seams

Abstract

Due to their tense mining succession relationship, gob-side roadways may undergo significant deformation under multi-mining pressure. In this article, many methods, such as on-site research, a theoretical analysis, a numerical simulation and an industrial experiment, are used to research the mechanism of asymmetric floor heave in a gob-side coal roadway affected by mining pressure during the mining of extra-thick coal seams. Our main research is as follows: (1) By monitoring the floor deformation in the roadway on site, it is concluded that the roadway floor shows asymmetry, indicating that the floor displacement near the coal pillar side is relatively large. (2) Based on a lateral overburden structure model of the roadway, the calculation formulas of the horizontal vertical stress caused by the roadway excavation and the excavation of the upper working face are derived separately, and the vertical stress coupling curves on both sides of the roadway during the mining of the upper working face are obtained through a numerical simulation. It is concluded that the cause of the asymmetric floor heave in the roadway is an uneven distribution of vertical stress. (3) The numerical simulation shows a symmetrical distribution of the floor displacement curve during the roadway excavation with a max. displacement of 49.5 mm. The floor displacement curve during the mining of the upper working face is asymmetric with a max. displacement of 873 mm at a distance of 1 m from the central axis near the coal pillar side. The range of the plastic zone in the roadway gradually expands with the mining of the upper working face, and the maximum depth of floor failure is 5.5 m. (4) According to the cooperative control principle of “roof + two sides + floor”, an asymmetric floor heave joint control scheme of “floor leveling + anchor cable support + concrete hardening” is proposed. The floor deformation monitoring results indicate that the max. floor heave at the measurement point near the coal pillar in the roadway is 167 mm, and the floor heave is effectively controlled.

Failure properties of roadway with extra-thick coal seams and its control techniques

“…In order to research the surrounding rock stress evolution laws and deformation features of the roadway with thick top coal, the similarity models [ 2 ], the Hoek-Brown failure criterion [ 3 ], the field measurement and the numerical simulation methods have been applied by many scholars. Based on the relevant research results, it is well known that the superimposed mining stress which induced by the large mining thickness of the coal seams and the intense movement of the overlying strata could aggravate the deformation and instability failure of the roadway with thick coal roof [ 4 ], the supporting system and its efficiency will gradually decrease [ 5 , 6 ] during this process, and the asymmetric floor heave and significant deformation was more easily appear for gob side roadway in extra-thick Coal Seams [ [7] , [8] , [9] ]. In order to control the surrounding rock deformation of the roadway with extra-thick coal seam, the dense combined supports have to be applied in roadway construction on site, which significantly reducing the driving efficiency and leading to the technical problem of mining proportion imbalance in the mine [ 10 ].…”

Floor Heave Control in Gob-Side Entry Retaining by Pillarless Coal Mining with Anti-Shear Pile Technology

“…Zhu et al [32] proposed the control method of "bottom lifting + bottom angle bolt + floor bolt" based on the results of a numerical simulation. Wang et al [33] proposed an asymmetric floor heave control scheme of "floor leveling + anchor cable support + concrete hardening" on the basis of the control principle of "roof + two sides + floor". Wei et al [34] used 3DEC discrete-element software to simulate and analyze the characteristics and evolution of asymmetric roadway floor heave under dynamic-load disturbance, and proposed the asymmetric control scheme of "slurry anchor reinforcement + top cutting and pressure relief".…”