Mechanism and control technology of top coal squeezing and fracture ofgob-side entry driving in fully-mechanized caving mining face

In view of the horizontal squeezing and fracture of the roof coal in the fully.mechanized caving roadway driving along gob under unstable overburden, No.103 working fow of Wangjialing mine was used as the engineering background, a comprehensive method including filed investigation, theory analysis and numerical modelling was employed to analyze the deformation and failure mechanism and corresponding control technology. The results shows:①Under the influence induced by fracture and rotation movement of unstable overlying strata, the roof coal body undergoes obvious squeezing movement in the horizontal direction, causing the superficial coal mass to be squeezed, displaced and broken. ②A unstable mining stress σj exerted on the coal mass surrounding the gob side entry in the vertical direction was induced by the rotation movement of the key blocks, meanwhile a compression stress σd exerted on the coal pillar in the inclination direction was also induced; the interaction between the two is the root cause of squeezing and fracture and instability of the top coal mass；③The horizontal displacement of roof on coal pillar side is about 240 mm and and the deformation of the top of the solid coal side is about 40mm. The significant difference of the displacement of the top plates on both sides will inevitably lead to the displacement and slip between adjacent rock layers and the occurrence of squeezing and fracture, and the 0 level displacement point is significantly offset from the center of the top plate to the solid coal side. ④The roof control of the roadway along the gob under unstable overburden was not only to strengthen the support of roof in the coal pillar side, but also to improve the adaptability of the support structure to the horizontal movement. According to this, the "high-strength bolt support + anchor cable" scheme is proposed, and the steel combined structure in the roof was applied in the field. Field engineering practice indicates that this support technology can effectively control the deformation of the coal mass surrounding the gob-side entry driving.