| Based on the observation results of strata behavior,the roof failure mechanism of large-section coal roadway under the severe mining influence and the subarea control of surrounding rock are studied detailedly by research methods such as the determination of rock mechanics parameters,the mechanical modeling,the numerical analysis and the industrial test.Moreover,some concrete issues of coal roadway under the severe mining influence are analyzed in this paper,mainly including its failure characteristics,the subarea by the intensity of mining influence,the failure and movement law of its overlying strata,the mechanism and the key influencing factors of its roof separation fault,the bidirectional control mechanism of high prestressed truss cable,the strengthening control technology of its surrounding rock which is varied from different subarea,the industrial test of a typical large-section coal roadway in Wangjialing coal mine,etc.The main conclusions are as follows:(1)According to the results of laboratory physical and mechanical properties test,the surrounding rock of the typical coal roadway under the severe mining influenc belongs to the class V,which has the characteristics of short self-stabilization time and easy instability.Concluded by field investigation,the 440-550 m in the 20102 tailentry is affected by severe mining,of which the surrounding rock is serious instable.Besides,although the 0-440 m in the 20102 tailentry is out of the mining influence of the adjacent working face,there are some searious damages in this subarea.If there is not any measures to be used,the degree of the damages would be further aggravated.(2)After the field investigation and the numerical modeling analysis of the strata behavior,it is found that the area affected by severe mining in fully mechanized top-coal caving face ranges from the 80 m in the front of the working face to the 130 m behind the working face.Meanwhile,the concept of the partitioning by the different intensity of severe mining influence is put forward on the basis of the failure characteristics in different area of the coal roadway.The 20102 coal roadway is divided to three areas: the I area influenced by dynamic mining pressure,the II area influenced by dynamic pressure of mining and excavating,the III area influenced by static pressure after mining.(3)According to the analysis on the comprehensive index of deviatoric stress invariant,it is found that the change form of tensile strain lag is the key factor that affects the intensity of dynamic mining influence on surrounding rock of coal roadway.Co MPared with the I area and the III area,the tensile strain lag is more obvious in the II area influenced by dynamic pressure of mining and excavating.Moreover,the shallow surrounding rock of coal roadway roof is seriously damaged,of which the strain type belongs to the tensile strain;the middle surrounding rock maintains a higher degree of distortional strain energy,and the strain type is transformed from the tensile strain to the plane strain,which shows the obvious lag transformation;when it comes to the deep surrounding rock,the strain is a single compressive strain.(4)Based on the fracture articulated characteristics of overlying strata,the mechanical model of the articulated structure of overlying rock block is established,and the calculation method of the bearing load of the surrounding rock under the mining influence is put forward.The calculation formula is as follows.In this formula,q4 represents the uniformly distributed load of the coal pillar side under the mining influence,Fs represents the load of the solid coal side under the mining influence.(?)(5)The motion law of the large structure in overlying strata is analyzed by using the numerical simulation software of discrete element.It is found that the severe rotary subsidence of the block B will directly cause the sharp sinking of the roof in the vertical direction and the extrusion shear failure of the main roof into the inside of the roadway in the horizontal direction,which increases the plastic zone depth of the coal pillar.Besides,the damage in the surrounding rock of coal roadway intensifies the movement of the overlying strata structure,and even causes the another fracture,which deeply destroys the stability of the surrounding rock.Moreover,the surrounding rock displacement of the coal roadway under the static pressure is mainly the vertical displacement;with the occurring of the horizontal displacement,the vertical displacement is further intensified when the coal roadway is affected by the severe mining.However,whatever the coal roadway is affected by the static pressure or the severe mining,the surrounding rock displacement is still mainly the vertical displacement.(6)Based on the calculation methods of the beam's vertical deflection and the beam's horizontal displacement in the mechanics of materials,it is found that the strata fault in the coal roadway roof occurs after the strata separation,and the strata separation only occurs when the maximum deflection of the upper strata is smaller than that of the lower strata.After summarizing the characteristics of overburden rock structure under the severe mining,the coefficient KC of the strata fault and the strata instability is brought to analyze the separation-fault criterion of coal-rock seam in the coal roadway roof.The criterion formula is as follows.(?)(7)The numerical simulation schemes of the strata separation-fault factors are designed based on the principle of orthogonal test.It is found that the 3 key factors affecting the strata vertical separation are the bolt length,the top coal strength and the relation of excavation and mining;the 3 key factors affecting the strata horizontal fault are the cable angle,the top coal thickness and the relation of excavation and mining.Besides,the interaction relationship between the strata separation-fault and the related factors are discussed detailedly in this paper.(8)A new type of the prestressed truss cable structure is developed in this paper to solve the strata separation-fault occured in the coal roadway roof affected by severe mining;and the control system of the high prestressed truss cable is put forward to improve the surrounding rock control of the coal roadway.The control system can make a bidirectional positive response to the vertical separation and the horizontal fault occured in the coal roadway roof.The control effect of the coal roadway in which the control system is used at the site is prominent especially in the complex environment such as the large section,the severe mining influence,the weak roof,the high stress and the large overhanging roof area.(9)Based on the characteristics of the truss cable which is tight fit with the roof in the working condition,the structural mechanics model of the composite beam which is consist of the roof and the truss cable is established to analyze the control mechanism of the truss cable to the vertical deflection and the horizontal fault of the coal roadway roof.The structure bearing model of the truss cable is established to calculate the minimum tensile strength and the pretightening force of the truss cable material,which is laid a theoretical foundation for the design of support scheme.(10)Based on the study of the partitioning by the different intensity of severe mining influence,the enhanced control concept of the different subareas classified by the different intensity of severe mining influence is put forward in this paper.The failure characteristics of the surrounding rock in each section of the coal roadway are analyzed to point out the corresponding control mechanism of each section;the support schemes of each section are developed by using both of the numerical analysis and the field practice.The support scheme of the I area influenced by dynamic mining pressure shows as follows: the supporting system formed after the original support repairing?using the truss cable to control the strata separation-fault of the roof?reinstalling the anchor cable to prevent the extension of the plastic zone ?installing the single hydraulic prop to improve safety;the support scheme of the II area influenced by dynamic pressure of mining and excavating shows as follows: the repair system of the reconstructed anchor is put forward,of which the main part is the multi support structure of the bilateral control;the support scheme of the the III area influenced by static pressure after mining shows as follows: the multiple support structure combined with the truss cable,the single anchor cable and the bolts,is used to reduce the mining influence of the working face.(11)The industrial test of the support scheme used in each section is carried out,then the monitor of the roof separation and the surface displacement is carried out to evaluate the control effect on the surrounding rock of the mining coal roadway.The monitor result shows that,under the severe mining influence of the adjacent working face,the maximum displacement of the roof and floor is about 138 mm,and the maximum displacement of the two sides is about 117 mm,which proves the better control effect of the support scheme designed in this paper. |
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