| Based on the National Natural Science Foundation of China(51474218)and the 3206 mining roadway in Nanguan Mine,this paper studies the relationship between the concrete-filled steel tubular support and its combined support with anchor and netting.Aims to improve the concrete-filled steel tube for underground engineering.The design of the bracket provides a favorable basis.This paper studies the mechanism of CFST short columns from the most basic CFST short columns and measures the ultimate bearing of CFRP short columns with different wall thickness.Force,and the relationship between the Poisson's ratio and the load of the specimen under different wall thicknesses,and then studied the relationship between the steel tube and the core concrete according to the theory of elastic mechanics and defined the definition of the thin-walled CFST short column.There is a critical point in the ratio of wall thickness to diameter.When it is larger than this value,the axial stress of the steel pipe is not consistent with the actual force.When it is less than this value,the axial stress of the steel pipe presents pressure.Different calculation methods for ultimate bearing capacity of thin and thick-walled CFST short columns are presented in combination with experiments.The calculated results are in good agreement with the experimental results.Then the mechanism of the circular arch of concrete filled steel tube under the mean loading of six equal points is studied.The ultimate bearing capacity and deformation and failure characteristics of CFRC arch with different span ratio and steel fiber volume are measured by structural experiments.The increase of the span ratio can improve the ultimate bearing capacity of the circular arch,while the increase of the steel fiber volume parameter reduces the ultimate bearing capacity of the circular arch,indicating that the CFRC circular arch is affected by the axial force under the six-point equivalent loading.Greater than the bending moment.Through the numerical simulation,the stress distribution in the elastic range of the arch and arch bottom section and the plastic range are analyzed.The influence of different wall thickness,different section size and different span-to-span ratio on the ultimate bearing capacity of CFST circular arch is also analyzed.It is pointed out that the cross-sectional dimension of the wall thickness is greater than the span ratio greater than the wall thickness.According to the elastic center method of the arch bridge,the axial stress,bending moment and shear force of each section of the CFST circular arch under unit force are calculated.Combined with the experimental results and numerical simulation results,a reasonable assumption of the section strength is given.The interaction mechanism between the steel tube and the core concrete in the short column is proposed.The calculation method of the ultimate bearing capacity of the CFRC circular arch under the equivalent loading of six equal points is obtained.The calculated results are in good agreement with the experimental results.In the study of the joint mechanism of concrete-filled steel tubular frame and anchor-plate retaining and the surrounding rock,the similar model test of four sets of circular roadways were designed,which were unsupported roadway,bolting net support roadway and concrete-filled steel tube support.Roadway(hereinafter referred to as bracket support roadway),steel tube concrete support and anchor-plate retaining combined support roadway(hereinafter referred to as support support roadway).The problem of difficult to embed the anchor in the circular roadway was solved during the implementation of-the similar model test.Through model test analysis,the deformation and failure characteristics of surrounding rock,surrounding rock displacement and surrounding rock stress of unsupported roadway,bolting and meshing support roadway,support roadway and combined support roadway are compared.The test pointed out:Without support roadway,the bottom lines monitoring line flrst loosened,and then the roadway walls part cracked.As the load increased,the crack of the roadway walls part expanded to the tunnel roof,accompanied by the falling of the roadway walls and the tunnel roof.The anchor-plate retaining support roadway:the roadway walls and the roof monitoring line have loosed at the same time,and the range of relaxation is large,indicating that the anchor net spray support can make the broken surrounding rock and the deep surrounding rock form a continuous deformation overall.When the load is increased,the phenomenon of bottom drum is prominent,the shoulder steel strip is bent,some of the anchor rods are embedded in the surrounding rock,and the tunnel roof is partially collapsed.The bracket supports the roadway:and brackets of roadway walls firstly contact the surrounding rock and plays a certain supporting role.The roadway walls have no deformation,and the roof and bottom of surrounding rock are in an unsupported state,and the change of the top and bottom surround rock are similar to that of no support.Continue to load,the top arc arch span ratio increases,the top arc arch bearing capacity also increases,the arc arch bearing capacity of the roadway walls is reduced.Finally the roadway presents an elliptical shape.The combined supports roadway:in the early stage of support,the deformation characteristics of the roof surrounding rock are similar with thar of the anchor-plate retaining support.Differently,the support firstly contacted with the roadway walls,which leads to the monitoring line of tunnel walls unloosening:Compared with the bracket support,the roof monitoring lines have a larger loosening range.The effect of combined support is significantly better than the anchor-plate retaining support and the bracket support.Finally,according to the elastoplastic theory,considering with the reasonable thickness of the spray layer and the influence of the anchor cable,compression on ring support theory is optimized.Through numerical simulation experiments and similar model tests,the anchor-plate retaining support,bracket support and combined support are analyzed.The effects of three kinds of support forms,such as anchor-plate retaining supports,bracket supports and combined supports are analyzed.By analyzing the influence of brackets,anchors and anchor cables on shallow surround4ng rock,the compression on ring support theory is confirmed.Finally,the applicability of the pressure ring theory is confirmed by typical engineering examples. |
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