Failure Mechanism And Control Of Surrounding Rock Of Reserved Roadway Under The Influence Of Upper And Lower Coal Seam Mining

The deformation and damage of the surrounding rock of the reserved roadway has been the focus and difficult point in the field of roadway support.The serious deformation and demage of roadway surrounding rock has hindered the mining of mining face,and has also took a series of safety hazards,such as roof fall accident,broken anchor bolt and anchor cable hurting human accidents,which has brought great pressure to safety production of the coal mine.Reserved roadway is one of the two roadway of the working face,which is left to serve for the next working face.The roadway is often affected by two or more mining disturbances and prone to severe deformation and damage.The two levels of Panel 1 Coalseam NO.2-2 and 4-2 in Buertai Mine are simultaneously mining,and the overlapped layout of the working face and the roadway at the top and bottom two coal seam.In the early stage of coal mine operation,the upper coal seam face was first mined,followed by the lower coal seam face,under the influence of superimposed stress,there were serious floor heave,roof subsidence and coal side deformation and failure in reserved roadway of upper coal seam,with an average floor heave of 2.2m,the roadway was abandoned because it could not be controlled,and finally a roadway was re-excavated,which seriously affected the safe production of coal mine.Therefore,in order to solve this problem,detailed analysis is needed.The plastic damage of roadway surrounding rock is the main cause for deformation and damage.The geometric size and shape of the plastic zone determines the destruction characteristics and the scope of the surrounding rock.Therefore,to reveal the deformation and damage mechanism of the reserved roadway is to study and analyze the formation and development of the plastic zone of the roadway surrounding rock.This paper takes the reserved roadways under the influence of the working face mining of Buertai Mine in Shendong Mining Area as the engineering background,and adopts comprehensive research methods such as theoretical analysis,on-site monitoring,laboratory tests,numerical simulation,and industrial tests to form the plastic zone of surrounding rock of the roadway,from the plastic zone of surrounding rock of formation and development,to reserved the roadway surrounding rock deformation and damage characteristics,the evolution and dynamic spatial stress following mining under the influence of mining deformation mechanism,reserved roadway butterfly plastic zone malignant extended support resistance on the mechanism,the plastic zone of surrounding rock stress control surrounding rock control technology in the system research,has made the following main conclusions and innovations:?1?Through three methods of surface displacement,deep base point displacement and roof drilling peeping,the deformation and failure characteristics of 22103 return airway in Buertai Mine were monitored in detail,the deformation and failure rules of reserved roadway in different stages were obtained.There was no deformation and damage in the surrounding rock of roadway during the driving;during the first mining of the same coal seam,there was a slight shallow layer damage in roadway surrounding rock,which mainly shows delayed damage,the roadway in front of work was basically free from deformation and failure,deformation and failure of roadway at50m behind the working face began,deformation and failure of roadway remained stable within 200m⁴50m area behind the working face;during the period of superposition mining in upper and lower coal seam,the surrounding rock of reserved roadway was severely destructed,50m in advance working face roadway began to undergo deformation and failure,with the advancing of working face,the degree of deformation and failure was gradually aggravating,the deformation and failure of roadway surrounding rock was characterized by"big top and bottom,small sides",the maximum displacement of the roof and floor was 2.2m,and the maximum of coal sides was 1.53m.?2?Core sampling work was carried out in 22103 return airway of Buertai Mine,through the physical and mechanical parameters experiment of coal and rock,the rock structure and its mechanical properties of reserved roadway roof were obtained;roof lithology was mainly sandy mudstone and sandstone,the uniaxial compressive strength of sand mudstone is 19²6MPa,tensile strength of sand mudstone is 0.76⁰.93MPa,uniaxial compressive strength of sandstone is 28³5MPa,tensile strength of sandstone is 0.83¹.41MPa,which belongs to a project of soft surrounding rock,at the same time,the elastic modulus and Poisson's ratio of surrounding rock of roadway roof were obtained.?3?Taking the 22102 working face of Buertai Mine as the engineering background,the distribution characteristics and laws of stress field around the coal seam after the first mining of the same coal seam were obtained by the FLAC³DD numerical simulation.The lateral 0³m range of the working face was in the high stress ratio band,the ratio is 1.7⁵.7,and the lateral 11.25³0.75m range of the working face was in the low stress ratio zone,the ratio was 1.26¹.3.When the 20m coal pillar was reserved,the reserved roadway was in the low stress ratio band.The stress field of reserved roadway was related to the location of the working face.The front face had little change compared with the original rock stress field.The maximum principal stress behind the working face increases gradually,the maximum value was1.47 times of the original rock stress,and the angle between the maximum principal stress and the Z axis was deflected from 90 degrees to 48 degrees.?4?Taking the 22102 working face and 42102 working face of Buertai Mine as the engineering background,the distribution characteristics and laws of the stress field around the stope after the overlay mining of the upper and lower coal seams were obtained by the FLAC^3D numerical simulation.The lateral stress ratio range of the upper coal face increased,and the 0³m increases to 0⁵1.75m,and the maximum principal stress increased.When the 20m coal pillar was reserved,the reserved roadway was in the high stress ratio zone.Retention of roadway surrounding rock and stress field should be corresponding to the position of the lower coal working face about space,in front of the 0⁵0m range in low stress ratio,principal stress ratio was1.43¹.61,50m⁴50m behind working face were at the high stress ratio,principal stress ratio was 1.84².22,the maximum principal stress and the Z axis angle between39.7°⁴1.9°.?5?The mechanical mechanism of the formation of plastic zone around circular roadway under bi-directional non-isobaric conditions was revealed,the influence of surrounding rock cohesion,internal friction angle,ratio of main stress,minimum principal stress value and direction of maximum principal stress on the shape and geometry of the plastic zone of the surrounding rock of a circular roadway was obtained.The rock cohesion and internal friction angle was negatively related with the size of the plastic zone,the greater its value,the plastic zone size was larger,the shape of plastic zone was close to butterfly or butterfly;principal stress of rock mass and the ratio of the minimum principal stress value and the plastic zone size was positively related to the size of the plastic zone.The greater the value,the plastic zone size was larger,the shape of plastic zone was close to butterfly or butterfly;the plastic zone of the surrounding rock had the characteristics of direction,with the direction of maximum principal stress change occurred in butterfly shape deflection,maximum plastic zone stress in the direction of the maximum and minimum principal,oval shape the maximum plastic zone occurred in the direction of minimum principal stress.The most sensitive factor in the formation of the butterfly plastic zone was the ratio of stress.?6?Taking the 22102 working face of Buertai Mine as the engineering background,by means of FLAC^3D numerical simulation,the distribution characteristics and laws of the plastic zone of surrounding rock in the 22103 return airway during the excavation stage and the first mining stage of the same layer coal were obtained.During excavation,the plastic damage scope of reserved roadway surrounding rock was small,the top and bottom of plastic damage depth was 1.5m,coal sides of plastic damage depth was 0.75m;once mining in the same coal seam,plastic zone of reserved roadway in front of working face was basically unchanged,the plastic failure depth of reserved roadway behind the working face increased gradually and then tended to be stable,the plastic damage depth of top and bottom was 2.25m,plastic damage depth of coal sides was 1.5m.?7?Taking the 22102 working face and 42102 working face of Buertai Mine as the engineering background,through the FLAC^3D numerical simulation,the formation and development rule of butterfly shaped plastic zone in 22103 return airway under the influence of the upper and lower coal seam mining were obtained,the failure mechanism of the surrounding rock of reserved roadway was revealed.After the lower coal face was excavated,in front of the working face 50m,the main stress of the reserved roadway began to increase,and the plastic zone of the surrounding rock began to expand;after 50m behind working face,reserved roadway keep under high stress ratio,principal stress the value also increased gradually,butterfly damage pattern began to occur and expanded rapidly,at 400m after the working face,the principal stress tended to be stable,and the plastic zone of the surrounding rock is stable,the plastic damage was most serious at this time,plastic damage depth of roof was 7.5m,plastic damage depth of floor was 4.5m,plastic damage scope of floor was very large and was connected with plastic zone of coal pillar side,plastic damage depth of coal pillar side was 3m,plastic damage depth of coal wall side was 2.25m.?8?Theoretical analysis and numerical simulation had proved that,although supporting resistance and plastic zone of surrounding rock were positively related,however,the numerical value between supporting resistance and surrounding rock stress field was quite different in engineering practice,the influence of supporting resistance on plastic zone range of surrounding rock was limited,especially in high stress environment,supporting resistance played a very small role in roadway with large plastic damage.The size of plastic zone of surrounding rock was mainly controlled by original rock stress field or superimposed mining stress field,and support resistance can not change the initial plastic zone size and shape formed under the stress condition of surrounding rock.?9?Through FLAC^3D numerical simulation,the plastic zone distribution characteristics of surrounding rock of 22103 return airway under different supporting resistance in Buertai Mine were analyzed.there are three supporting conditions for 1cables of?15.24×6500mm per meter,1 cables of?15.24×6500mm and 1.5 cables of?17.8×8000mm per meter,1 cables of?15.24×6500mm and 5 cables of?17.8×8000mm per meter,maximum plastic damage depth of roof surrounding rock was 7.5m,maximum plastic damage depth of floor surrounding rock was 4.5m,maximum plastic damage depth of coal pillar side is 3m,maximum plastic damage depth of coal wall side was 2.25m,and the plastic zone of roadway was basically same.?10?Because supporting resistance can not reduce size of surrounding rock plastic zone size from the engineering scale,the key to control surrounding rock of reserved roadway under influence of upper and lower coal seam was to control the formation and development of the irregular butterfly shaped plastic zone.Most of butterfly deformation and destruction of surrounding rock of reserved roadway were caused by the action of mining stress,therefore,the control idea of reserved roadway surrounding rock was mainly by stress control,and the roadway supporting and the surrounding rock reinforcement were supplemented.Aiming at the technical conditions of Buertai Mine,the stress regulating and controlling technology for changing coal pillar size and horizontal distance between upper and lower coal seam faces was put forward,through numerical simulation analysis,increasing size of coal pillar could reduce magnitude and ratio of principal stress,thereby reducing plastic damage scope of surrounding rock,when the size of coal pillar was greater than 55m,the plastic zone of surrounding rock was greatly reduced;after the horizontal separation of upper and lower coal seam working face was increased,although the minimum principal stress increased slightly,the ratio of principal stress decreased,according to theory of butterfly plastic zone,the scope of plastic zone of roadway surrounding rock had also decreased greatly;when the horizontal distance between upper and lower coal seam working face was greater than 120m,the plastic area of reserved roadway surrounding rock decreased greatly.?11?Industrial tests were carried out in NO.2-2 coal seam and NO.4-2 coal seam in Buertai Mine,by stress control method of increasing horizontal distance between upper and lower coal seam working face,the situation of serious deformation and damage of reserved roadway was improved.Speed up the pushing rate of NO.2-2 coal seam,slow down or suspend NO.4-2 coal seam working face,when two coal seams were separated from a working face and the distance is 508m,the deformation and failure of surrounding rock of reserved roadway at upper coal seam was obviously improved,the deformation of roof and floor and two sides of surrounding rock decreased greatly,the surrounding rock controlling technology provides a good reference for the same type of roadway.