Study on failure characteristics and control of roof separation with weak interlayer of deep gob-side entry driving

Roof with weak interlayer has significant influence on the stability of deep gob-side entry driving, to effectively control the separation of roof with weak interlayer in deep gob-side entry driving under high deviatoric stress, based on the mechanical experiment of composite specimen with weak interlayer and numerical simulation experiment of gob-side entry driving under the influence of mining, the influence of the thickness, number and position of weak interlayer and the evolution law of roof separation under high deviatoric stress conditions are obtained, the main reasons for separation of the roof with weak interlayers of deep gob-side entry driving are elucidated. The key points for controlling the roof with weak interlayer are analyzed using the mechanical model of cantilever beams under the support load and coal pillar support load, and the separation control method is subsequently proposed. The results show that the influence on the deterioration of the mechanical properties of the composite gradually becomes larger with the increase of the thickness and the number of layers of the weak interlayer, the influence on the deterioration of the composite with weak interlayer at the low position is stronger than that at the high position. The fracture of the composite specimen is produced by the weak interlayer, and the characteristics of the fracture development are different with its thickness, the number and position. The main shear failure zone generated at the left shoulder corner of the roof and connected to the adjacent rock failure area near the weak interlayer after gob-side entry driving, resulting in the separation of the weak interlayer, and the development morphology of main shear failure zone and non-coordinated degree deformation of roof vary with the deviation angle of principal stress and the thickness, number and position of weak interlayers, which revealed the instability mechanism of roof with weak interlayer of deep gob-side entry driving. The mechanical model of roof separation under the support load and the supporting load of coal pillar was established, which found that the separation of weak interlayer in the anchorage zone was 79% lower than that outside the anchorage zone, the degree of influence on the spatial distribution of separation under different influencing factors is as follows: supporting load of pillar, supporting load of roof, elastic modulus of the roof. According to the separation law and control points of the composite roof with weak interlayer in the deep gob-side roadway, the following separation joint control method was proposed: increasing the bearing capacity of coal pillars, reducing the development of the failure in roof and increasing the deformation coordination of roof with weak interlayer. The maximum separation of the roof is 10 mm according to on-site separation monitoring, indicating that this method can effectively control the separation of the roof with weak interlayers.