| Shendong mining area is a key construction project in the largest coal production base with the deep implementation of the west development strategy and the coal resource depletion in the eastern China.However,with the mining scale and mining depth increasing,there remarkably occur the high rock pressure dynamic disasters of surrounding rock generated by a thick hard roof in the mining area,this badly affects the safe and efficient production.The fully mechanized caving face with a thick and hard roof in the Buertai Coal Mine of the Shendong Mining Area acting as an engineering background,combining theoretical analysis,similar simulation,numerical calculation with engineering practice,this paper systematically studies fracture mine pressure characteristics of thick hard roof under strong mining,its fracture structure and evolution law,and the load transfer mechanism of the fracture of the thick hard roof under the strong mining,and the control method of the near and far field of the fracture structure of thick hard roof under the strong mining.This paper achieves the following findings:(1)Taking a fully mechanized caving face NO.42107 of Buertai Coal mine in Shendong Mining area as the research object,this paper clarifies a law of mine pressure appearance induced by the fracture of thick hard roof under strong mining in Shendong mining area.Based on this mine pressure characteristics,this paper expounds an evolution process of overburden structure of the fracture working face of the thick hard roof under strong mining,and the timing sequence effect and regional characteristics of crack development and evolution of the thick hard rock under strong mining.Therefore,this paper proposes an idea of ‘ far-field overburden structure ’ and‘ near-field bearing structure ’ derived from the fracture migration of thick and hard rock under strong mining.(2)Based on evolution characteristics of the fracture structure of thick hard roof overlying rock under strong mining,this paper illustrates an energy storage function of suspended thick hard rock stratum and development and thorough evolution process of‘ O-X ’ crack,explains relations between evolution features and migration of cantilever rock beam structure in direct roof strata and articulated rock beam structure in thick hard strata under strong mining,and further interprets an structural form of ‘ inner beam and outer arch ’ of thick hard roof overburdened rock fracture under strong mining,and reveals structural characteristics of the interaction between the ‘ far-field overburden structure ’ derived from the thick and hard rock strata fracture and the‘ near-field bearing structure ’ of surrounding rock of lap joint coal rock mass below.(3)According to the fracture structure,evolution law of thick hard roof under strong mining,aiming at the interaction between thick hard roof and lap joint coal rock mass below under the effect of strong mining,the paper establishes a mechanical model of space structure of thick hard roof under strong mining,a deflection function equation of thick hard rock strata under the strong mining,elaborates energy storage mechanism of thick hard roof under strong mining and the major controlling factors causing disaster.(4)This paper builds a constitutive model of overburden rock migration and energy storage-time domain evolution of thick and hard roof under the strong mining,establishes stress-strain relationship expressions of the mechanical constitutive models of lap joint coal rock mass below,immediate roof rock and suspended thick hard rocks,deduces a load-deformation evolution function of overburden rocks under the strong mining and an energy storage state function of such rock strata.Based on the theoretical study of overburden rock load-deformation relationship and energy storage state of thick and hard roof under the strong mining,this paper reveals crack development evolution process and energy storage and transportation process of the suspended thick and hard rock strata under the impact of mining,and inverts a mechanical transfer model of the ‘ far-field overburden structure ’ derived from the fracture of thick and hard roof under the strong mining to the ‘ near-field bearing structure ’ of the surrounding rock of the lap joint coal rock mass below.(5)Based on the study of the fracture structure and mechanical constitutive model of the thick hard rock strata under strong mining,this paper explains a strength weakening regulation mechanism and space energy storage structure of the thick hard rock strata under strong mining,and uncovers the control parameters of the ‘ inner beam and outer arch ’ structure and the near-far field strength of the thick hard roof overburden fracture under strong mining.Moreover,this paper expounds control principle of space energy storage structure and strength weakening control principle of thick hard roof under the strong mining,proposes the control method of near-far field of fracture structure of thick hard roof under the strong mining.This paper further clarifies the evolution process of overburden structure changing from a disaster inducing structure of ‘ inner beam and outer arch ’ to a pressure yielding structure of‘ front beam and rear arch ’ under the action of regulation,reveals the interaction mechanism between the overburden fracture structure and the overburden load under the action of regulation.(6)Using numerical simulation calculation,this paper studies an evolution process of the bearing structure and stress distribution of surrounding rock in gob-side roadway under different mining conditions,interprets the positive correlation between stress concentration degree of surrounding rock in gob-side roadway and strength of the thick and rock.Then this paper reveals cumulative effect of ‘ far field overlying rock structure ’ derived from the thick and hard rock fracture under the strong mining on the load transfer of ‘ near field bearing structure ’ of surrounding rock in gob-side roadway and the influence of plastic zone and stress distribution of surrounding rock of retaining roadway.And in this paper,a method is proposed to control the stability of surrounding rock in gob-side roadway by improving the strength of ‘ near field bearing structure ’ and weakening the strength of ‘ far field overlying rock structure ’ derived from the thick and hard rock fracture.(7)Engineer practice in this paper is performed about how to control the near-far field regulation of strong mine pressure of surrounding rocks in the thick hard roof fracture under strong mining in Shendong Mining area,the technology of far field subsection hydraulic fracturing under strong mining is applied to the working face NO.42202 of Buertai Coal mine in Shendong Mining area.Besides,roof cutting grouting technology of near field gob-side roadway on construction is applied to auxiliary transport NO.42107 of Buertai Coal mine in Shendong mining area.And finally,monitoring results of in-situ rock pressure show that the strong rock pressure in mining field has been effectively controlled,and that the surrounding rock stability of gob-side roadway has been significantly improved.Fig.ure [118] Table [12] References [246]... |
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