Study On Support Technology Of Large Section Soft Rock Roadway In Hongliu Coal Mine

The geological conditions of Hongliu coal mine are complex.The roof of the roadway has weak lithology and low strength.It is a argillaceous cemented composite roof.The pores of the main roof contain water and are close to the coal seam.During the excavation of the mining roadway in I020207 working face,the roof locally bursts water,and the mudstone softens and collapses when encountering water,resulting in the failure of the "bolt anchor cable anchor mesh" combined support system,large roadway deformation and difficult support.At the same time,in order to meet the needs of equipment installation and auxiliary transportation in fully mechanized mining face with large mining height,the section size of mining roadway in working face is large,with roadway width of 5m,height of 4.4m and section area of 22m2.Therefore,the mining roadway in the working face of Hongliu coal mine belongs to a typical large section soft rock roadway.The contradiction between roadway surrounding rock deformation and control is becoming more and more prominent,which seriously restricts the safe and efficient production of the mine.The surrounding rock deformation control and support technology of mining roadway has become the primary problem to be solved urgently.Based on the analysis of the failure theory of the surrounding rock of the large roadway,this paper puts forward a new supporting scheme for the large roadway,which has a good supporting effect.The problem of difficult support of large section soft rock roadway in Hongliu coal mine is effectively solved.The specific work is as follows:(1)Firstly,this paper analyzes the engineering geological conditions,roadway excavation technical parameters,roadway surrounding rock deformation characteristics and deformation influencing factors of return air roadway in 1020207 face of Hongliu coal mine,and determines the roof rock composition and physical and mechanical parameters.The total thickness of direct roof and false roof of return air roadway in 1020207 working face is 6.8m.It is a argillaceous composite roof,which is supported by 2.5m anchor bolt,6.3m anchor cable and anchor mesh.Through field observation,it is found that the typical feature of the mining roadway in 1020207 working face is that the deformation of surrounding rock in the roof drenching area is large,while the deformation of surrounding rock in the area without roof drenching is small.Based on the analysis of geological conditions,tunneling parameters,roof lithology and roadway deformation characteristics,a reasonable conjecture is put forward.During the roadway excavation,the direct roof of the roadway is thin and uneven in thickness.The local anchor cable leads to the main roof,resulting in the downward seepage of pore water in the main roof.The argillaceous composite direct roof softens and expands when encountering water.The failure of the original support system is the main reason for the large deformation of surrounding rock.Under the condition of no water in the roof,the strength of the original support system meets the requirements,the surrounding rock control effect is remarkable,and the disturbed cracks in the roof are not developed to the main roof.(2)Roof water inrush is the main factor causing the difficulty of roadway local support.Through the analysis of surrounding rock stability,the deformation characteristics of roadway surrounding rock are obtained,and the real cause of roof water inrush is clarified.Firstly,the calculation formula of plastic zone radius of roadway surrounding rock is deduced based on Mohr-Coulomb strength criterion.Considering the residual cohesion and friction angle of soft rock mass,the calculation formula of plastic zone radius of surrounding rock deduced based on Mohr-Coulomb strength criterion is improved.It is calculated that without considering the support,the plastic zone of roadway surrounding rock extends about 2.8m from the roadway wall to the depth of surrounding rock.Secondly,by means of numerical simulation,the control effect of the original support system of the roadway on the surrounding rock of the roadway under the condition of no water is analyzed,the size of the plastic zone is determined,and the stability of the roadway is studied.Both theoretical analysis and numerical simulation show that the surrounding rock deformation control effect of the original support system is good under the condition of no water.The comprehensive analysis verifies the reasonable conjecture of the cause of local water inrush from the roadway roof.(3)According to the theory of bolt(cable)reinforcement and composite arch,the relationship between the thickness of composite arch and the length of bolt(cable)in arch roadway is deduced.It is calculated that the effective length of bolt(rod)cable should not be less than 4.1m.Through theoretical analysis,in order to ensure sufficient support strength,and the principle that the anchor cable does not penetrate the roof and directly conduct the pore water of the main roof,it is determined that the reinforcement length of the anchor cable at the roadway arch is 4.3m,and the anchor length remains unchanged.Two improved roof support schemes of "bolt anchor cable anchor mesh anchor shotcrete" and "full anchor cable anchor mesh anchor shotcrete" are further proposed.Through numerical simulation analysis,it is concluded that the development range of surrounding rock plastic zone of "bolt anchor cable anchor mesh anchor shotcrete" support system is significantly increased,and the roof cracks are developed,which may develop to the main roof when the local direct roof of the roadway is thin,so there are certain potential safety hazards.The use of 4.3m full anchor cable reinforcement can effectively limit the development of the plastic zone of the roadway roof,the deformation of surrounding rock is small,the roof crack and anchor cable do not conduct the pore water of the main roof,and the support effect is good.(4)The on-site monitoring was carried out during the excavation of the return air roadway of i020208 working face adjacent to 1020207 working face and with the same geological conditions.The roof was supported by 4.3m full anchor cable,and there was no water inrush during the excavation.The field monitoring results show that under the new support conditions,the maximum displacement of the top and bottom plate is 50.3mm,and the maximum displacement of the two sides is 72.3mm.In the reinforcement area of arch crown anchor cable,the maximum separation is 18.9mm.At the measuring point 8.0m away from the roadway surface,the maximum separation value is 28.1mm.There is no strong floor heave,wall falling and roof falling,which ensures the safe mining of the working face.Good support effect has been achieved.Based on the practical problems in the field,this paper systematically and comprehensively studies the surrounding rock support technology of large section soft rock mining roadway in Hongliu coal mine,analyzes the deformation law and causes of roadway surrounding rock,puts forward a reasonable improved support scheme,and obtains good practical application.This work provides a theoretical basis and guidance for the study of surrounding rock deformation law and support design under similar geological conditions,and provides a useful reference for the surrounding rock deformation control of mining roadway under similar geological conditions in Ningdong mining area.