Research On Design And Optimization Of Extensible Energy Absorbing Anchor

There are two projects that support the research,the NSFC project of study on strata control and surface subsidence law of fully mechanized longwall mining with steep seam,and design and experimental study on the cyclic yield anchor bolt with large deformation of Hunan Graduate Innovation Fund.The failure forms and causes of bolt are analyzed.The deficiency of the common anchor in deep support is summarized.Two type of new yield bolts are proposed.Through the comparison of theory and experiment,it can be concluded that the extensible energy absorbing bolt is the best structure.The structural parameters optimization of the extensible energy absorbing anchor is carried out.Finally,the ideal mechanical properties of the optimized energy absorbing bolt is obtained.The traditional bolt support theory and the surrounding rock loose circle support theory are introduced.The main failure forms of bolt support,the mechanical behavior of loaded anchor and the failure mechanism of bolt are analyzed.It is concluded that the main failure mode of bolt support in deep roadway is broken failure.There are two reasons for the failure of anchor bolt,which are external loading and mechanical properties.The strength of anchor bolt determines the stress compensation which can be used to limit the deformation of the surrounding rock.The amount of extension determines the amount of pressure during the support period.Through the analysis of the failure mechanism of the anchor bolt,it can be concluded that the common bolt can not adapt to the stress and deformation of the deep surrounding rock,and can not meet the engineering requirements.Two new energy absorbing anchors are proposed.The structure composition,working mechanism and mechanical principle of pressure structure are introduced respectively.The contrast test of the mechanical properties of the bolt’s pressure structure is carried out.Experimental results show that two kinds of anchor bolts both have the mechanical properties of yield.The extensible energy absorbing anchor bolt can keep the basic constant resistance during the drawing process.The cyclical yield anchor bolt with large deformation has a large resistance value at the first yield period in the drawing process,but later stage the work resistance significantly reduced.The drop is large and the working performance is unstable.By comparison,the structure of the energy absorbing bolt can be identified as superior.The strength of the energy absorbing sleeve of the extensible energy absorbing bolt is checked.The optimum range of the wall thickness of the energy absorbing sleeve is obtained.The mechanical analysis of the plug of the extensible energy absorbing anchor is carried out.The optimum range of the pressure angle of the resistance plug is obtained.The mechanical properties of the energy absorbing structures at optimum range were tested.It is concluded that the lower limit of the wall thickness of the energy absorbing sleeve is inversely proportional to the thickness of the plug at the same bolt diameter.When there is a certain thickness of the resistance plug,there is a positive relationship between the lower limit of wall thickness and the diameter of anchor bolt.The mechanical characteristics of different section forms of energy absorbing sleeve are analyzed.According to the cross section,the punching die is manufactured.The cold pressure test of the seamless pipe is carried out by the mould.The cold pressing scheme with different cross sections is obtained.The complete energy absorbing bolt is machined.The static pullout test is carried out.The test results verify the bolt has the mechanical properties of yield and energy absorption.The extensible energy absorbing anchor bolt shows relatively stable mechanical properties.