Theory and application of roof superimposed beam support of coal roadway based on effective anchorage layer thickness

By analyzing the deformation and failure characteristics of roadway roof strata，the macro process and mechanical phenomenon of roof instability are obtained. According to the stratification characteristics of sedimentary strata of coal roadway roof，the mechanical model of superimposed beam is established. Based on the coordinated deformation and common bearing characteristics，the equivalent bearing stress，interlayer force and bolt/cable support strengthening parameters of each layered rock beam in the superimposed beam are solved. The supporting mechanism of bolt/cable on the superimposed beam structure is revealed. The bolt/cable on the superimposed beam structure optimizes the bearing stress distribution of each layer of roof with different bending stiffness，gives a full play to the mechanical bearing performance of each rock stratum，and controls the overall subsidence of the roof. In addition，it improves the cohesion and deformation modulus of the superimposed beam and indirectly strengthens the mechanical bearing strength of the overall anchored structure. According to the instability conditions of the superimposed beam support structure in different service stages，the effective anchorage state and the effective anchorage layer thickness of the roof support of coal roadway are proposed for evaluating the actual anchoring ability of the bolt/cable to the roof in roadway support. This forms the roof superimposed beam support theory of coal roadway. Based on the support theory，taking the return airway of the Ⅱ7324S working face of Renlou Coal Mine of Wanbei Coal Power Group as the engineering background，the roof support design is carried out under the conditions of ultra close coal seam and supporting roadway under goaf. The roadway is divided according to three different ranges of layer spacing more than 6，4-6 and 2-4 m. By analyzing the roof superimposed beam structure and calculating the effective anchor layer thickness，the support scheme based on anchor bolt and grouting anchor cable is determined to strengthen the roadway roof in different roadway areas，and the rationality and effectiveness of the support scheme are verified combined with the field industrial tests.