Short Encapsulation Pullout Test Method And Application Based On Equivalent Radial Stiffness

Bolt support technology has been widely applied in many fields.The anchoring system transfers the load from the unstable surrounding rocks to the stable ones through the anchor rod,which improves the surrounding rocks’ bearing capacity and realizes the anchoring system’s optimization results.The anchoring force,which is generated and interacted between the anchoring part of the bolt and the surrounding rocks through the bolts,is an important index towards the mechanical parameters of the load transfer capacity of the system and plays a decisive role in the anchoring effect.Therefore,the accurate measurement and application of anchoring force is the foundation of bolt support design and the basis of numerical calculation of surrounding rock deformation and control means,which is of great significance to engineering practice.In this dissertation,theoretical analysis,indoor short sleeve pull-out test,numerical calculation,and field engineering verification were all used to study.Based on the load transfer mechanism of anchor mechanics,the theory of the thick-walled cylinder was applied in the research of anchorage mechanics laboratory;Short Encapsulation Pullout Test(SEPT)was carried out,simulated and anchored the equivalent radial stiffness analysis method of surrounding rocks through the calculation of radial stiffness of surrounding rock,socket,get a set of wall thickness and material mechanics parameters,the calculation formula of equivalent mechanical parameters of surrounding rocks.The radial extruding effect of resin ring on hole wall and the anchoring effect of resin ring by rod body during pullout process are analyzed by using the circumferential strain variable of the sleeve.Based on the analysis method of equivalent radial stiffness established in this paper,sleeve materials and wall thickness parameters of different surrounding rocks were proposed to simulate the coal mine site.It was concluded that PVC,6061 aluminum,and 20 steel sleeves with corresponding wall thickness could simulate the equivalent radial stiffness of soft,semi-hard,and hard surrounding rocks,respectively.The corresponding simulation methods of different sleeve materials in the laboratory and different surrounding rock properties in the field were established.Based on the laboratory short encapsulation pullout test,the principle of stress influence of the radial stiffness of the sleeve on the anchoring performance of the anchor solid was raised.Based on the theoretical analysis model,the negative exponential relationship between the average anchoring force peak value of the bolt and the radial stiffness of the surrounding medium was revealed.Through data fitting,the relationship between the anchoring force peak value of the left-handed anchor solid and the right-handed anchor solid and the elastic mechanical properties of the surrounding rock was obtained.The equivalent radial stiffness method is used to carry out numerical calculations and field industrial tests.The analysis results show that the anchorage force parameters calculated by the theoretical method are closer to the field practice,and present the conformability with the field test results.In this dissertation,the equivalent radial stiffness theory was used to establish the simulation method of different radial stiffness sleeve materials in the laboratory and different surrounding rock properties in the field.The principle of stress influence on anchor solid’s anchoring performance was studied through the short pull-out test of different radial stiffnesses in the laboratory,and the anchoring force prediction expression under different radial stiffnesses of surrounding rock was established,which was validated by numerical calculation and field test results on site.The research results of this paper provide a theoretical basis and technical support for the mechanical mechanism and performance analysis of the field anchoring system and the design of bolt support schemes in the future.In this dissertation,there are 97 figures,13 tables,and 158 references respectively.