Study On Compressed Arch Of Anchor Rod And Reasonable Support Parameters In Deep Mudstone Roadway

As the roadway excavation technology becomes increasingly mature,shallow coal resources have been basically exhausted.Relevant data show that the reserves of shallow coal mines are far from meeting the needs of social and economic development.Along with the increasing depth of roadway excavation,the increasing degree of loose and broken rock and the deteriorating property of rock,the difficulty of excavation increases day by day.Therefore,mining of deep coal resources and technological innovation have become a key problem to be solved.At present,the main technology of roadway support is the combined support of anchor cable and anchor rod.As a good form of active support,anchor rod support has a great influence on the effect of roadway support.In view of the different properties of rock strata in the excavation of roadway,it is necessary to make comprehensive analysis and consideration on the selection of reasonable parameters of bolt support.A large number of practical experience shows that the reasonable selection of bolt parameters will directly affect the stability of roadway surrounding rock.But at present,the layout of bolts in roadway support is mainly based on experience and the empirical analysis method of surrounding rock classification without displaying the advantages of bolt support.Therefore,the study of bolt support parameters,such as pre-tightening force,spacing,length and other reasonable parameter has become very meaningful and provided reference values for the roadway safety and economy in real production and life.By means of numerical simulation,800 m of surrounding rock-rock mudstone is buried in the roadway.When using ss constitutive model,different parameters(pre-tightening force,length,spacing)of anchor rod are selected,and FLAC 3D model is established by measuring the parameters of rock mechanical properties in laboratory.This study observes the displacement and additional stress values of roadway under different anchor arrangement,and uses TECPLOT software to slice the section and process the relevant data.After the slice processing data is imported to ORIGN software drawing chart,it clearly reflects the displacement and additional stress changes.Anchor rod support can restrict the deformation of roadway to a certain extent,ensure the stability of surrounding rock,reduce the breaking degree of rock around roadway,improve the stress condition,and reduce the displacement of rock in all directions of roadway.Under the condition of mudstone,the additional stress is closely related to the pre-tightening force,length and spacing of anchor rod.Based on the 1.5 m of bolt spacing,the influence of the additional stress value on the pre-tightening force of the bolt is studied.Previous studies have shown that the necessary condition for the compressed arch under horizontal additional stress is0.07 Mpa,and for the compressed arch under vertical additional stress is 0Mpa.As the pre-tightening force of 0 KN,40 KN,80KN,100 KN and 120 KN increases,the peak of additional stress value increases gradually,and the thickness of compressed archunder horizontal additional stress increases.During the study of the change of the additional stress value with the bolt length 1.0m,2.0m,2.2m,2.5m and 2.8m,it is found that the magnitude of the peak value of the additional stress is positively correlated with the increase of the bolt length,and the thickness of the compressed arch also increases.After analyzing the influence of bolt pretension and bolt length on additional stress,the influence of bolt spacing on additional stress is discussed.According to the condition of arch formation,when the spacing of anchor rods is less than 0.4 m,the compressed arch under triangular additional stress with anchor rod as central axis can be formed,and superimposed on each other,which is beneficial to the stability of roadway.The influence of different pre-tightening forces on the displacement is investigated by taking the length of anchor rod 1.5m and spacing 1.0m as the initial conditions while considering the additional stress.The pre-tightening force 100 KN is determined to be the optimal condition by the comparasion of the pre-tightening force0 KN,40 KN,60KN,80 KN,100KN and 120 KN.When the pre-tightening force100 KN and spacing 1.0m have been determined,the optional length of anchor rod2.5m can be obtained by changing the length 1.5m,2.0m,2.2m,2.5m and 2.0m.Thus,the influence of spacing is further deduced.Comparing the anchor rod spacing 0.6m,0.8m and 1.0m,the support effect is best when the bolt spacing is 0.6m.The optimum supporting method in soft rock is obtained with the bolt pre-tightening force 100 KN,the length 2.5 m,and the spacing 0.6 m.The principle of economy is also taken into account when selecting the optimum parameters of anchor rod.The change of plastic circle of surrounding rock is observed in the process of selecting parameters.It is found that in the process of selecting parameters,the plastic circle of surrounding rock is decreasing continuously,and the supporting effect is also increasing continuously.