Mechanism And Control Technology Of Strong Rock Pressure Induced By Structural Instability Of Hard Roof In Thick Coal Seam

The hard rock stratum has the characteristics of thick and hard to break.With the advance of the working face,it is difficult for the hard rock to collapse without taking measures,resulting in a large area of hanging roof.When the advancing distance reaches the roof caving distance,the hard roof suddenly break and collapse,forming strong dynamic load,and the superposition of dynamic and static load leads to the strong ground pressure behavior of the working face.Therefore,aiming at the problem of strong ground pressure in the working face caused by the failure of the hard roof in thick coal seams.This paper uses theoretical analysis,rock mechanics test,physical similarity simulation test,numerical simulation test and field test.Based on the engineering background of hard roof mining of No.3 coal in Huainan Pan'er Mine and No.8 coal in Shendong Baode Mine.The fracture evolution characteristics of hard rock strata,the dynamic and static mechanical properties and energy evolution of coal-rock assemblages,the characteristics of strong ground pressure induced by the failure of hard rock strata and the stress evolution characteristics of hard roof coal seams were studied.The technique of preventing strong ground pressure in hard roof coal seam was proposed.(1)A model of a thick plate of hard roof was established.The three-dimensional accurate analytical solution of the stress distribution of the elastic thick plate at the initial pressure on the working face was obtained.The fracture evolution process and fracture morphology of the hard roof during the first weighting were studied.The influence of rock thickness and compressive strength on the accumulation and release characteristics of elastic energy of hard rock was discussed.It provides theoretical basis for mechanism of coal and rock disaster and control mechanism of hard rock working face.(2)The mechanical characteristics of coal-rock combination under dynamic and static loads were obtained.The energy evolution characteristics and acoustic emission characteristics of coal-rock combination under static loads were analyzed.The mechanical characteristics and energy dissipation of coal-rock combination with different strength under dynamic loads are studied.The energy conversion mechanism of deformation and failure of coal-rock combination was revealed,It provides experimental basis for the study of the fracture characteristics and disaster mechanism of hard roof under dynamic and static loads.(3)The physical simulation and numerical simulation models of single-layer hard roof and double-layer hard roof were constructed.The characteristics of fracture instability and overburden migration of hard roof were analyzed.The mechanism of strong ground pressure induced by fracture and instability of hard roof was revealed.The stress evolution of coal seam and hard rock stratum in the process of mining hard roof coal seam was analyzed.The static load characteristics of hard rock strata on coal body was obtained.(4)The prevention and control technology of strong ground pressure in hard roof coal seam mining was put forward.According to the characteristics of strong strata behavior of No.3 Coal Seam in Huainan Pan'er coal mine and No.8 coal seam in Shendong Baode coal mine,deep hole presplitting blasting and directional drilling hydraulic fracturing technology were used to weaken the hard strata.The field monitoring data show that the periodic weighting intensity and the periodic weighting intensity decreases.The problem of strong ground pressure in the working face of hard rock strata has been effectively controlled.Figure[79]table[12]reference[154]...