Study On Surrounding Rock Stability And Control Of Deep Roadway In Thick Coal Seam Under The Action Of Tectonic Stress

With the increase of coal mining depth, support of roadway in thick coal seam is getting difficult, and especially under the influence of high tectonic stress, supporting problem becomes more outstanding. Based on the analysis of distribution characteristic of tectonic stress field in deep strata, synthetically using theoretical analysis, numerical simulation, similarity simulation experiment and field test, surrounding rock stability principle and controlling technology of roadway in coal seam, containing roadway along coal seam roof and roadway with thick top coal under the action of tectonic stress in deep strata, have been studied. Main results are as follows:(1) By analyzing ground stress in Juye Mine Area, distribution laws of ground stress field at the depth of over one kilometer in this mine area have been obtained. Horizontal stress plays a leading role in stress field, and the maximum horizontal principal stress is generally 30~ 40MPa. The maximum horizontal principal stress is 1.5~3.2 times of vertical stress. The azimuth angle of maximum horizontal stress is about N60°E, with average angle 30°between it and regional tectonic stress direction (east to west). Back analysis of ground stress field near the fault shows that stress gathers near the fault, especially in the ends of fault, the maximum horizontal principal stress reaches to above 40MPa and stress direction changes dramatically, the maximum horizontal principal stress directions deflect 30°~ 60°.(2) Distribution characteristics of surrounding rock plastic zone, displacement and stress was analyzed, and the deformation and failure mechanism of roadway in thick coal seam under the action of tectonic stress in deep strata was revealed: Two sides slide along bedding plane of roof or floor, and the higher tectonic stress is, the bigger slippage amount becomes, the slippage amount to be an important component of two sides relative displacement distance; increasing of difference value of vertical stress and horizontal stress near the bedding plane prompts weak rock failure near the bedding plane, so plastic zone of surrounding rock develops into deeper along the bedding plane.(3) The plane strain similarity simulation experiment method was applied to analyze the function mechanism of buried depth, tectonic stress, bedding surface on deformation and failure of thick coal seam roadway. The results of experiment show that the bigger buried depth tectonic stress are, the top coal transverse bending deformation, slippage and moving along horizontal joints and shear failure is more obvious, and shear failure of roof bolt is more likely to happen. Numerical simulation method was used to analyze deformation and failure characteristics and mechanism of roadway with thick top coal under the action of tectonic stress in deep strata: shear failure of bedding surface between top coal and roof prompts to form "inverted trapezoid"plastic zone in top coal, which means that the instability area is large, even causing top coal collapse.(4) Mechanics analysis model of shoulder bolt was established to analyze the action of slippage of bedding plane on bolts. Shoulder bolt breaking mechanism under the action of tectonic stress in deep strata is discovered. Under slippage shear force produced by tectonic stress, the shear force of shoulder bolt is biggest in bedding plane, and the bolt body is cut off because of this. Under slippage shear force and eccentric load of steel belt produced by coal deformation, breakage easily occurs in the bolt end.(5) Focused on the problem of large slippage deformation of coal sides and shoulder bolt breakage,"high strength and high pre-tightening bolt support, and controlling and yielding coupling support"surrounding rock control technology was put forward for roadway along coal seam roof under the action of tectonic stress in deep strata, whose function mechanism are: to allow coal sides to have certain slippage deformation along roof, namely take"yielding"means, and limit the expansion of plastic zone in shoulder coal, namely take "controlling" means. Combination of both means can realize instability of surrounding rock and supporting structure. Focused on the problem of"inverted trapezoid"plastic zone of top coal in thick coal seam roadway,"high strength and high pre-tightening force bolt support, diagonal cable beam supporting and shoulder coal reinforcing supporting"surrounding rock control technology was put forward, whose function mechanism are: to effectively reduce the bending and sinking of top coal, prevent the formation of"inverted trapezoid"plastic zone of top coal, and obviously improve the stability of thick top coal.(6) Based on surrounding rock stability and control principle of roadway in thick coal seam under the action of tectonic stress in deep strata, focused on production and geological conditions of Xinjulong Mine, whose buried depth of roadway is 800 m and the maximum horizontal principal stress is 30~40 MPa, industrial test was carried out in main roadway for transportation of north area and mining roadway 1301N fully-mechanized top coal caving face. Field application shows that"High strength and high pre-tightening bolt support and shoulder controlling and yielding coupling support"technology for roadway along coal seam roof, and"High strength and high pre-tightening bolt support, diagonal cable beam support on top coal and shoulder coal reinforced support"technology for roadway with thick top coal under the action of tectonic stress in deep strata, can effectively control the deformation of surrounding rock, and realize the stability of surrounding rock and supporting structure.