| Surrounding rock control of deep gob-side entry retaining is one of the problems in the field of roadway support.Specially,the roof directly is relating to the success or failure of gob-side entry retaining,to realize control of roof strata is the key to surrounding rock stability of deep gob-side entry retaining.In this paper,the researches on roof disaster characteristics and control technology of deep gob-side entry retaining are systematically developed through engineering investigate and survey,laboratory experiments,theoretical analysis,physical simulation and numerical simulation etc.It clarifies roof disaster-causing mechanisms of deep gob-side entry with different overlaying strata and the key factors of roof instability,and reveals movement pattern of overlying strata and its mechanical mechanisms,roof control mechanisms,and proposes critical techniques of roof strata control and develops systematical evaluation methods of roof stability.Research achievements have been successfully applied to deep gob-side entry retaining engineering.The main conclusions are as follows:(1)Roof failure form of deep gob-side entry retaining is divided into 8 types,i.e.roof bending subsidence,cutting roof along backfill,roof caving on solide coal side,large span roof caving,backfill rotation,backfill collapse,roof step,roof sliding along solide coal side.The roof failure shape of deep gob-side entry retaining is obviously asymmetric in horizontal direction and vertical direction.(2)Considering rock strength,thickness,relative position and collapse form,4 types of the overlaying strata structures of deep gob-side entry retaining have been classified,i.e.thin roof,thick roof,thick and hard roof and multi-thin roof.(3)Deep gob-side entry retaining model is built by physical simulations experiments platform,failure processes of the overlaying strata and evolution law of crack propagation at different stages are studied,asymmetric failure law of roof,deformation position and degree roof are realized.The fracture propagations process of overlaying strata is: roadway excavation?fracture increase in shallow roof?fracture of filled area roof caused by mining process?backfill fracture under eccentric load?rapid subsidence of roadway roof?external crack drum and rib spalling of solid coal side?acceleration unbalance of roof strata,it will eventually lead to roof instability of deep gob-side entry retaining.(4)Considering propagation law of plastic area in surrounding rock mass,for 4 types of roof conditions,serious deformation area,failure degree and failure scope have been systematically studied.The conclusions have been obtained:(1)plastic damage are mainly located at sides and floors of surrounding rock in gob-side entry retaining with thin roof and thick-hard roof;(2)the scope and depth of plastic damage of surrounding rock mass are large,however,plastic damage of backfill is not obvious;(3)plastic damage are mainly located at sides of surrounding rock in gob-side entry retaining with multi-thin roof.(5)Considering stress field and displacement field of surrounding rock,the order of stress field for gob-side entry retaining with different roof conditions is: thick-hard roof>thin roof>multi-thin roof>thick roof.The order of damage degree of for gob-side entry retaining with different roof conditions is: thick roof>multi-thin roof>thin roof>thick-hard roof.(6)Based on dynamic response characterization of roof migration failure in horizontal and vertical direction,roof disaster-causing mechanisms of gob-side entry retaining with different roof conditions are studied,and the initial and critical points of deformation and failure of roof support structures are specified.The Initial and key factors of roof support structures for gob-side entry retaining with thin roof and thick-hard roof are at backfill,coal side and floor.The initial and key fac tors of multi-thin roof support structures for thin roof are at backfill roof,backfill and floor.The Initial and key factors of roof support structures for gob-side entry retaining with multi-thin roof are at filled area roof,backfill and floor.(7)2 factors of roof disaster on deep gob-side entry retaining are studied,i.e.natural factors inclued high crustal stress,strata occurrence characteristics,fissure water and characteristics of surrounding rock structures.human factors include fierce mining influence,roadway section dimension,support factor and time factor.The main factors of roof separation and collapse are lithological difference and uneven distribution,non-coupling and low support strength of asymmetric surrounding rock structure,large span,and its fragmentation,dilatancy and long-term creep in strong disturbance and highly centralized stress state.(8)Based on regional morphology of roof separation in deep gob-side entry retaining,3 types of roof separation are classified,i.e.be nding subsidence type,tilt fault type and mixed type.From vertical and horizontal direction,roof separation degree is classified: fierce,medium and weak separation.Mechanical models of bending subsidence type and tilt fault type are built respectively,and then maximum critical values are calculated by following equations.Maximum critical value for bending subsidence separation:(?)Maximum critical value for tilt fault separation:(?)(9)The formation process of short cantilever beam structure of gob-side entry retaining is cleared after cutting or caving roof.3 types of short cantilever beam structure are short cantilever-articulated rock beam,short cantilever-step rock beam(I type and II type),mechanical interaction between different rock beam structure and surrounding rock support are analyzed.(10)Mechanical models for short cantilever beam structure and surrounding rock supporting structure are established.formation mechanisms of different short cantilever beam structure are clarified,and the basic criterion for different short cantilever beam structure formation is determined.As sliding instability coefficient K?1,short cantilever hinged beam structure is formed.As K<1,short cantilever stepped beam(I and II type)is formed.Further,effects of thickness and length of basic roof,thickness of roof and coal seam on short cantilever beam structure are determined.(11)A “multi support structure” control system for deep gob-side entry retaining roof is proposed,consisting of bearing capacity enhancement of anchorage system,intensity of crack coal-rock mass,colla-borative bearing structure of roof and sidewalls,as well as unloading and span-cut,which can ensure the structural integrity of roo f and improve the coordination bearing capacity of roof and sidewalls.(12)The critical technology of coupling support by division in surrounding rock of deep gob-side entry retaining is proposed.4 classes and 9 supporting zones are divided,including co upling support of roof 3 zones,combined support of 2 zones of solid coal seam,composite bearing structure of roadside 3 zones and auxiliary support in different stages.Support mechanical effects and maintaining roof stability are detailed analyzed in every zooms.(13)New truss and anchor rope structure with horizontal bidirectional constant resistance function is designed to effectively control asymmetric deformation and failure in vertical and horizontal direction in deep gob-side entry retaining,whic h consists of two anchor cables and short channel steel composite beams close to the roof rock surface.In particular,short channel stee beam includes main beam,secondary beam and 2~3 U type cable.The secondary beam is inserted into the main beam to overlap with a certain length and is fixed with a U type cable.(14)Geometric and mechanical properties of new truss and anchor rope structure are analyzed and strength of this structur e is tested.The bidirectional control mechanism of new truss and anchor rope is cleared,i.e.when the roof is in the failure form of extrusion and loose expansion,if the bearing force of short channel steel composite beam in the axial direction is greater than the static friction resistance of cable assembly,short channel steel composite beams can be moderately stretched or indented,adapting to the horizontal compression of the roof strata.(15)The extension theory and analytic hierarchy process of matter element concept are used to select and explore 15 evaluation indexes and their weights for roof disaster instability of gob-side entry retaining.A comprehensive evaluation model with multi-level and multi-index is constructed,which is based on class ical domain matter element,domain matter element and correlation function in the extension set.O n this basis,the corresponding digital comprehensive evaluation system is developed to improve the efficiency of the evaluation system.(16)The “multi support structure” control system and the critical technolog of coupling support by division in surrounding rock are employed in deep gob-side entry retaining in the eastern area of Panyi coal mine.Roof maintenance effect is better,it isn't obvious separation and fragmentation in shallow and deep roof.The roof supporting structure of deep gob-side entry retaining is more complete,satisfying ventilation safety and reuse security. |
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