Research Of Surrounding Rock Stability Control Of Floor Space Soft Rock Roadway In Gently Inclined Coal Seams Group

That the problem of floor space rock roadway influenced by short-distance coal seam group mining is common to many mines in China, the sophisticated deformation and destruction mechanism of high stress soft rock roadway under the influence of cross mining in particular. As a result, support becomes increasingly outstanding with great difficulty in stability control of surrounding rock. Surrounding rock stability control of floor space soft rock roadway in short-distance coal seam group mining is in the essence the support of soft rock roadway under repeated high stress, which remains to be a problem in the coal mine production and construction of China. Therefore, research of surrounding rock stability control mechanism under repeated mining influence and the deformation and destruction characteristics of floor space soft rock roadway is of great theoretical and engineering application importance.This paper, based on the engineering background of the north part of the LuBan mountain coal mine in south Si Chuan, by virtue of indoor experiments, on- the-spot detection, theoretical analysis and numerical simulation, detects the primary rock stress of experimental coal mine, physical mechanism of coal measure strata, creep characteristics and constitutive relation of floor space soft rock, and the thickness of loose circle in rise entry under different mining difference. The distribution and transmission of abutment stress in floor space in short-distance gently coal seam mining as well as the problem of layout and support of rise entry in coal seam cross mining are researched by numerical simulation. Theoretical analysis of the possible combined arch of bolt and surrounding rock and strengthened arch of anchor and surrounding rock in high stress soft rock roadway as well as mechanism of the two arches is presented in this paper. The design of support parameters is in accordance with loose circle thickness and coal mine stress demonstration in repeated mining of the air returning rise entry designed and enhanced by two arches in a selected mining area are made available. The main finding goes below:(1) The surrounding rock of floor space is classified according to the losses circle surrounding rock stability classification methods. The result goes that when not influenced by mining, rock of air returning rise entry of the experimental coal mine mainly falls into the second and third categories, i.e. rock of general stability. While under the influence of mining, it falls into the fourth and fifth categories, i.e., soft rock and rock with relatively low stability. The surrounding rock of rise entry is classified as standard high stress soft rock based on its mineral components stress distribution,and rock strength.(2) This paper has made a research on the creep characteristics and creep mechanism modeling of soft rock in floor space based on the characteristics of roadway deformation of air returning rise entry in the experimental area. The complete stress-strain curve of rock is achieved by singular stress experiment and creep experiments under different stress level in the curve are made. The experience constitutive relation and creep mechanical model of sandy mudstone are established according to creep deviation due to different loaded stress. The research finding of this paper can be used in the design and improvement of soft rock roadway in the north part of the Lu Ban mountain coal mine, adding and perfecting soft rock roadway support design.(3) Primary rock stress of the transportation crossheading at +285m level and loading tunnel at +450m level in the experimental coal mine are achieved by Kaiser Effects of acoustic emission and elasticity. Research shows that the primary stress field of the coal mine is of tectonic stress with few self-weight stress fields. The minimum primary stress is close to the self-weight stress of overhead surrounding and is compressive, providing boundary condition for the establishment of numerical model.(4) Research on abutment stress distribution in coal seam group by numerical simulation is made, and the result goes as: abutment stress ahead of the working face along the striking continues to transmit forward by the same stress wave with the progress of working face. The peak of stress ahead of the working face becomes stronger with the progressing working face. The area around the working face can be categorized into four areas as the elevated stress zone, distress zone and primary rock stress zone. During the mining of the 8th coal mine layer, two elevated stress zones occur ahead of the working face. The first is close to the wall, with a stress concentration parameter of 2.23. The second is below the elevated stress zone in the 3rd coal mine layer, with a stress concentration parameter of 1.18 and an influence area with a diameter of 60m. The abutment stress alone the inclination in the lower part of the coal mine is higher than that of the higher part, with a relatively higher stress concentration and influencing area. The influenced area of stress in the two sides of the 8th coal mine layer working face is larger that that of overhead working faces. (5) Research of stress distribution in floor space of the coal seam is made by numerical simulation and its result goes that the contour lineσ_y of coal mine under the working face inclines towards the front part of the inclination. While the contour lineσ_y of the rock in the gob is oval. With the progress of the working face, the three zones of primary rock stress, elevated stress, distress stress shall move forward, which bears direct influence to the extraction of the coal mine and roadway support. The abutment stress along the 8th working face in the transmission of floor space rock has a dynamic stress influence area of 35m.σ_y of the 8th working face alone the inclination becomes weaker as its distance from the coal mine layer increases. The abutment stress at the two sides of the gob along the inclination has a static stress influence area of 45m in its transmission in the floor space rock.(6) A research on the rational layout and size of coal pillar in the overhead mining area is made through numerical simulation. The research shows that an inner-crossing layout of 10m, 20m, and 20m for the second, third and eighth coal mining layer security coal pillar is reasonable. The influenced area in the floor space rock of the 8th working face is 35m. Based on this, the layout of floor space roadway can avoid or reduce the destruction of coal pillar abutment to roadway surrounding rock.(7) An analysis of the deformation and destruction characteristics of soft rock roadway surrounding rock in coal seam group mining and the control mechanism of soft rock roadway is made. The stability of rise entry surrounding rock is mainly under the influence of working face abutment stress of cross mining in the 8th coal layer. As the 2ed and 3rd coal mine layer are far from the floor space rise entry, they bear small influence to the stability of cross mining rise entry surrounding rock. It is noted that the dynamic stress influence of the 8th coal mine layer is very significant to the floor space rise entry at a horizontal distance -40m<x<60m from the 8th coal mine layer. The left sides of security coal pillar in the entire coal mine layer have no significant influence over the soft rock roadway surrounding rock stability. The research shows that the layout of floor space rise entry is best when at a vertical distance of no more than 45m from beneath the 8th coal mine layer and a horizontal distance of over 40m from security coal pillar.(8) Based on the relation among the thickness of loose circle in soft rock roadway surrounding rock, the combined arch of anchor and bolt, the enhanced arch of anchor cable, a two-arch system of anchor, bolt and cable for cross mining dynamic stress soft rock roadway pre-stress is established. By combing the inner edge of the enhanced arch of anchor and bolt and the outer edge of combined arch of anchor and bolt, placing the outer edge of the enhanced arch in the well preserved stable rock, and locating the boundary of loose circle in the center of the enhanced arch, the stress inside the rock is altered, thus, preventing the rock in the boundary of loose circle from deformation and destruction in greater depth, fixing the thickness of loose circle and controlling the deformation of roadway. Relative parameters for the thickness of combined arch of anchor and bolt, thickness of enhanced arch of anchor and cable, and support are determined in accordance with the thickness of loose circle of soft rock roadway surrounding rock, and are used for the control of soft rock roadway surrounding rock in mining. This support system is applied to roadway support engineering practice. The combined support of cable, net and anchor is of relatively efficiency, thus can be used to control deformation of soft rock roadway surrounding rock.