| With the gradual depletion of shallow coal resources,the mining depth and mining scale of coal mines have gradually developed toward large burial depths and large mining heights,and a large number of layered roof roadways have emerged.Due to the high complexity of the deformation mechanism of the layered roof and its distinctive features that are difficult to support,the stability of the layered roof severely restricts the safe and efficient production of the mine,and has become the focus and difficulty of current research in the field of rock mass engineering.In this paper,based on the previous research results,the horizontal layered roof of the roadway is taken as the research object.By establishing the mechanical model of the roof rock beam under the action of the vertical stratum load and the horizontal structural load,the distribution of the tension and compression domain of the layered roof is analyzed.Characteristics and the law of neutral layer migration.Considering the influence of the stability of the roadway roof on the effective span of the layered roof,the horizontal collapse width under different slab modes was studied,and the development height of the rock beam rupture area of the layered roof under different stable conditions of the roadway and its invisible rise were analyzed.The distribution characteristics of the falling arch,and then the optimal design of the supporting scheme and parameters of the layered roof are optimized.The main conclusions are as follows:(1)The mechanical model of horizontal layered roof under vertical load and horizontal structural load is established.The steady state of the roadway roof can limit the deflection displacement of the roof rock beam.The stress state of the roof rock beam is the fixed-supported beam model;the rock mass of the roadway roof deforms and becomes unstable under the support pressure,resulting in the deflection of the roof rock beam end.The force state will be converted from a fixed beam model to a simple beam model.(2)Using the theory of material mechanics and structural mechanics,the theoretical formulas of the deflection,bending moment and shear force of the roof rock beam are derived,and the mid-span extreme stress solution of any rock layer of the layered roof under the conditions of fixed and simple support is obtained.The extreme stress in the span of each rock beam of the roof is closely related to the lateral pressure coefficient,vertical ground stress,elastic modulus and effective span.Based on the layered roof equivalent analysis model,the mechanical criterion of the overall failure of the roof rock beam is discussed.When the equivalent maximum tensile stress on the middle and lower edges of the layered roof span is greater than its equivalent ultimate tensile strength,the layered roof The roof will be totally unstable.(3)The distribution rule of the neutral layer of the layered roof under different stable conditions of the roadway is analyzed.By establishing the stress distribution model of the horizontal layered roof rock beam under the combined action of vertical stratum load and horizontal tectonic load,the height of the tension zone and the position of the stress neutral layer of the layered roof under the conditions of fixed and simple support are studied.Under the condition of the same span,after the fixed roof rock beams are converted into simply supported rock beams,the height of the tension zone of the rock beams is reduced,and the position of the rock beam neutral layer will be shifted downward.The key influencing factors of the position of rock beam neutral layer are discussed.The results show that the position of the neutral layer of fixed-supported rock beams and simple-supported rock beams increases with the increase of lateral pressure coefficient and vertical in-situ stress,and decreases with the increase of the elastic modulus and thickness-span ratio of roof rock mass.(4)The influence of the stable state of the roadway roof on the effective span of the layered roof is discussed.Under the effect of supporting pressure,the rock mass of the roadway side section gradually developed from the split-slip type side to the single-slope shear type side,and the support position of the horizontal layered roof rock beam gradually shifted from the shoulder of the side to the deep part.Considering the influence of the rock stability of the roadway roof on the effective span of the roof,the effective span of the horizontal layered roof under the two conditions of split-slip and single slope shear is analyzed.(5)The distribution law of each rupture zone of horizontal layered roof is studied.Rock masses with tensile stress greater than zero below the neutral layer of the roof may break,and there may be a certain height of fracture zone below the neutral layer of each rock layer of the layered roof,based on the distribution characteristics of the neutral layer of the layered roof and the self-stabilizing stealth Based on arch theory,the height and width of the cracked zone of the layered roof under different roadway stability conditions were studied,and the distribution and vector height of the invisible falling arches in each rock layer of the layered roof were analyzed.The results show that the height of the rupture zone increases with the increase of the depth of the roadway ridge;the mid-span position of the neutral layer of each rock layer is the extreme point of the height of the invisible falling arch of the rock layer.(6)Optimized the support scheme under the condition of horizontal layered roof interval rupture.On the basis of theoretical analysis,the depth of roadway failure under different flank modes is calculated,and then the height of the tensile zone and the width of the fracture zone of each layer of the layered roof under different working conditions are determined.According to the height and position of the tension zone of each rock layer of the layered roof,the length of the anchor used for the support is determined,and the grouting amount is determined in conjunction with the volume expansion characteristics of the fractured rock mass of the layered roof.The original support design is optimized for the joint support of anchor and grouting.Through continuous on-site monitoring of the roof,the optimized support scheme has significantly improved the stability of the roof. |
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