Failure Mechanism And Stability Control Of Empty Roof In Roadway Rapid Excavation

The rapid excavation of coal roadway is an important supporting technology to improve the speed of single driving, to ensure the production replacement, to improve the mechanization level of coal mine, and is widely used in China. Workers often in the edge or the interior of the empty roof due to the excavation process, so the construction safety is affected by the roof stability. At the same time, law of the empty roof stability is the foundation of equipment and process and supporting design. Roof and floor of coal seam always associated with weak mudstone is easily broken and collapse because of untimely support or excavation disturbing. So the application of rapid excavation technology is troubled seriously by safety problems of empty roof.Aimed at the empty roof of coal roadway rapid excavation, using the methods of theoretical analysis, numerical simulation and field measurement, starting with the roof beam structure of empty roof, study stability law of empty roof and its main influence factors of coal roadway rapid excavation were studied, the deformation law of empty roof and the interaction relationship of head on structure and empty roof were revealed. Problems such as rapid excavation process, control technology of empty roof and corollary equipment were explored. The main results are as follows:?1? The stability mechanism of empty roof was studied by the roof structure: the bending modulus increases with the increase of the thickness, the roof deflection increases with the deep span ratio of the beam, and the support pressure in the coal wall also decreases. The roof stability would be weaken and the effective span of beam would increase due to the deformation of two sides. When self-supporting force of roof can bear the weight of itself and collapsing rock, sides anchor can significantly improve the compression and shearing capacity resistance of anchorage, reduce the span of broken zone and plastic zone, optimized roof stress, effectively control the deflection and subsidence of roof.?2? The influence factors of empty roof stability were analyzed: The plastic zone in the empty roof is elliptical whose long axis determined by head-on properties and short axis affected by stiffness of two sides. Vertical stress of empty roof is influenced mildly by circular distance which affect obviously continuing sinking of backside supporting roof. Increasing supporting strength cannot significantly reduce the subsidence of empty roof, but can improve the bearing condition to provide a better foundation for head-on advancing.?3? The evolution law of empty roof stability affected by head-on support structure and lagging support was revealed: the coupling state of lagging support and head-on "C" type supporting structure determines the subsidence and damage state of empty roof, its influence is divided into three stage: overlapping support, collaborative support, independent support. Technical ideas of "C+" coupling support of lagging support and head-on structure was formed on the basis.?4? The bending and sinking of roof easily lead to the tensile failure of immediate roof. Increasing empty roof distance makes head-on support and lagging support can only limit the vertical displacement of two ends of floating roof. Tensile stress distributes due to the unconstrained state in the middle of empty roof, and the peak value position posterior to the rear of empty roof where is the breakthrough zone of roof collapse.?5? Factors that affect the rapid excavation were analyzed by the principal component analysis method: human, machine, material, working method and environment. Efficiency of cutting head is a weakness in restricting the speed of roadway excavation. By comparing "S" type cutting trajectory and spiral cutting trajectory, the "S" type cutting trajectory of bottom-up path is more conducive to maintaining the stability of surrounding rock.Engineering exploreration was carried out with the rapid excavation case in Ji Ning 3_rd Coal Mine?...