Study On Coordination Relationship Between Prestress And Length Of Bolt And Bearing State Of Surrounding Rock Of Roadway

The deformation value and failure depth of roadway roof have the characteristics of "big middle and small sides".The same length and equal strength bolts are often used to support the roadway roof.There are problems that roof bolts can not coordinate the bearing capacity and give full play to their supporting effectiveness.Based on the engineering background of 11-3108 main haulage roadway in Menkeqing Coal Mine,this paper studies the coordination between the prestressing force and length of roof bolt and the surrounding rock of roadway by means of on-site investigation,geological grading evaluation,theoretical analysis,numerical calculation and engineering analogy,and puts forward and verifies the rationality and feasibility of differential support design.The main research results are as follows:(1)Analytic hierarchy process(AHP)is used to evaluate the grade of nine factors in three directions: Underground pressure,surrounding rock properties and engineering environment,so as to classify and support differential support.Finally,the differential degree of bolt support in roadway is divided into four grades.Combining with the mechanical test of coal samples under specific geological conditions,it is determined that the length of bolt in 11-3108 main transport roadway is 0.5-1 m higher than that of side bolt,and the prestress is 50-100 k N higher.(2)Based on the deformation and failure characteristics of roadway surrounding rock,the concept of differential support is put forward,and the theoretical basis of differential support research is clarified.On the premise of guaranteeing the support strength,the prestress and length of the middle bolt should be larger than that of the side bolt in order to adapt to the roof deformation characteristics;the distribution law of the depth of the balance ring in the state of self-stable equilibrium and ultimate equilibrium of the surrounding rock of the roadway is revealed,which serves as the basis for the design of the length of the roof bolt;the force model of the roadway roof is established,and the supporting effect of the prestress of the bolt on the roof and The characteristics of stress distribution can be used as the basis for the design of roof bolt prestressing.(3)The prestressing effect of roof bolts under equal and unequal lengths is simulated and analyzed.It is concluded that the central anchor prestressing plays a major role in controlling the roof deformation;when the prestressing is the same,the length of the side anchor is reduced by 0.5m,which can improve the stress and deformation state of the roof at the height of 1m,and verify the rationality of differential support.(4)Combining with the specific conditions of main haulage roadway 11-3108 in Menkeqing Coal Mine,the differential support scheme is put forward: the length of side bolt is 3.5 m,the prestress is 170 k N,the length of middle bolt is 4 m,and the prestress is 230 k N.By comparing with the original support scheme,the length of bolt is 4 m and the prestress is 200 k N,the mine pressure of roadway is better than the original support scheme,which proves the feasibility of differential support.(5)The results show that the working resistance of the side bolt is generally lower than that of the middle bolt and the design value.The initial prestress of the middle bolt has a significant effect on the increase of the working resistance of the bolt,which indicates that the strength of the two sides of the support is excessive.The rationality and feasibility of the differential support is verified on the side.