Fatigue Damage And Anti-fatigue Bolt Supporting Principle Of The Anchoring Body

Bolt supporting technology,widely used in mines,slopes,tunnels,and other engineering fields,has achieved huge economic and social benefits.However,anchoring parameters are often designed according to the principle of limit equilibrium in engineering design,ignoring the influence of anchoring-force fluctuations on the fatigue property of the anchoring body.In the actual working conditions of coal mine roadways,the anchoring force of the bolts in the roadway fluctuates constantly due to engineering disturbances such as the mining of the working face,roadway excavation,and blasting.The fluctuations of the anchoring force will cause fatigue damage to the anchoring bodies of bolts,which is related to the bearing capacity and stability of the surrounding rock of the roadway.The correlation between the anchoring-force fluctuation and the fatigue damage of the anchoring body should be analyzed for solving the failed anchoring body caused by the fatigue damage under complex working conditions.The work takes the anchoring body as the research object and simplifies the anchoring-force fluctuation as constant-amplitude fatigue loading.The fatigue damage effect of the anchoring body is revealed by the comprehensive use of the fatigue-damage-behavior experiment of the prestressed anchoring bodies of bolts and anchoring bodies of sandstone,analytical method,finite element method,finite difference method,on-site pull-out tests of bolts,industrial tests,and other methods.The fatigue damage effect of anchor bolt is revealed,the fatigue damage characteristics of anchor bolt are identified,and the fatigue damage mode of anchor bolt is distinguished.The analytical equation of the fatigue failure rate is deduced to determine the constitutive equation of the fatigue stiffness degradation of the anchoring interface.A finite element analysis model of fatigue damage is constructed to explain the influence of anchoring defects on the fatigue failure of the anchoring-body interface,with an improved method for the fatigue resistance of the anchoring body proposed.Besides discovering the mechanism of the anchoring-force fluctuation of the bolt,the principle of anti-fatigue bolt support is summarized and verified by engineering practice.The main research work is as follows:(1)The fatigue-damage-behavior experiment of the prestressed anchoring body is used to analyze the effects of loading amplitude,frequency,and pre-tightening force on the fatigue damage of the anchoring body.With the cyclic load of the same amplitude,the cumulative ringing count of the acoustic-emission parameters and the loading time conform to the curve of the logarithmic function,and the fitting formula was y=Aln(n/f)+B.The loading frequency accelerates the anchoring damage process and reduces the damage degree of the anchoring body.The greater the pre-tightening force,the stronger the ability of the anchoring body to resist cyclic loads.Besides,the ringing count in the acoustic-emission parameters is used to define damage parameter D_d of the cyclic load.The damage degree of the anchoring body under the cyclic load is quantitatively analyzed to infer the damage evolution process of the anchoring-body specimens after the cyclic load.The prestressed anchoring body after the cyclic load has higher stability.(2)The damage evolution process of the anchoring body of sandstone under the drawing of fatigue loading is described through the fatigue-damage-behavior experiment of the anchoring body and the acoustic-emission characteristic parameters monitored in the whole process.It is divided into the stages of elastic deformation,stable development,and fracture failure,revealing the evolution law of the anchoring-body fatigue damage of sandstone.The RA-AF correlation analysis method is introduced to identify the fatigue-damage properties of anchoring-body specimens at different stages.The clustering algorithm is used for the cluster analysis on the acoustic-emission characteristic parameters of the specimens under fatigue loading,thus identifying the fatigue damage mode of the anchoring body.(3)An analytical equation for the fatigue failure rate of the anchoring interface is proposed based on the double shear lag model.The fatigue failure of the anchoring interface can be divided into the initial,early,and later stages of fatigue.The interface failure length at the initial stage of fatigue is very little.The interface failure rate at the initial stage of fatigue decreases gradually after the maximum value of 0.0326 mm/time,and its reduction range at this stage is greater than 0.00001 mm/time.In the later stage,the fatigue failure rate of the interface is less than 0.0007553 mm/time,and its reduction range is less than 0.00001 mm/time.The failure rates of the interface at the early and later stages of fatigue show a decreasing trend,but the failure length continues to increase.Besides,the work discusses the influences of each material parameter in the analytical equation on the fatigue failure of the anchoring interface.(4)The theoretical model of interfacial fatigue in fibers is used to propose the constitutive equation of anchoring-interface fatigue stiffness degradation.Through the secondary development of the UMAT subroutine,the constitutive equation is embedded in ABAQUS to establish the finite element analysis model of fatigue damage.Moreover,the work proposes a numerical analysis method based on the Tresca yield criterion and the fatigue-degradation constitutive equation of the anchoring-interface stiffness.The monotonic-load and cyclic-load drawing experiments of the bolt are used to determine the key parameters in the finite element numerical-experimental parameters in fatigue stiffness degradation model of anchorage interface and shear strength of anchorage interface element in finite element model.The influences of anchoring-body sizes and material parameters on the fatigue damage of the anchor interface are analyzed,and the correctness of the finite-element numerical analysis method is verified through theoretical calculations.(5)The finite-element numerical analysis method based on Tresca yield criterion and fatigue stiffness degradation constitutive equation of anchorage interface is used to illustrate the interfacial fatigue-failure process of the anchoring body with defects,which is divided into the initial,early,and later stages of fatigue.The related effects on the fatigue damage of the anchoring interface are analyzed by combining the change curves of the axial stress and interface shear stress of the anchoring body with different defect lengths,positions,and distribution patterns at the initial,early,and later stages under fatigue loading.A device to increase the anchoring compactness and anchoring force of the bolt is designed to propose an improved method for the fatigue resistance of the anchoring body.(6)Relying on the engineering practice of the track tunnel along working face30104 of Youzhong Coal Mine under mining conditions,the finite difference method is used to analyze the dynamic load response of the anchoring-body particles in simple harmonic waves.The anchoring-force fluctuation mechanism of the bolt is as follows:dp1-2 is the displacement difference between the surface particles and the shallow part;dp1-2 is the displacement difference between the surface particles and the deep part in the anchoring range under dynamic-loading disturbance;d_{(dp1-2)-(dp1-3)}is the difference between dp1-2 and dp1-3;variable d_{(dp1-2)-(dp1-3)}acts on the bolt to cause the anchoring-force fluctuations.Furthermore,the principle of anti-fatigue bolt support of roadways is summarized.The anti-fatigue bolt supporting scheme along the track tunnel of working face 30104 is designed according to the related principles.The results of mine pressure monitoring verify the rationality of the supporting scheme in controlling the anchoring-force fluctuations of bolts,indicating the correctness of the anti-fatigue bolt supporting principle.