Numerical Analyses Of The Effective Bonding Length Of Bolts Based On A Cohesive Zone Model

Interface bonding between bolt and grout body is the base that they can work together. Due to the high strength of the bolt, usually a bond failure is induced by low interface strength in anchor reinforcement in the geotechnical engineering.Hence it is necessary to further study the interface between bolt and grouting body.This article, based on the bolt pull-out experiment, analyzed theoretically the interface bond-slip behavior of bolt and grouting body and proposed the interface bond-slip model of bolt and grouting.Based on the proposed bond-slip model, the pull-out process of the bolt can be divided into four stages, The corresponding interfacial shear stress, slippage and the axial stress analytical solution, and the formula for the ultimate bearing capacity corresponding to the four stages were presented.In this thesis, the main research work and achievements are as follow:(1) The reinforcement of rock with bolt is obvious and widely used, so it is very necessary to study the force mechanism of bolt in the bulk rock and the stress distribution. Then the research status of bolt anchoring is described from three aspects-experimental research, theoretical derivation and numerical simulations. At last the main research contents and the methodology are put forward.(2) This thesis introduces the material constitutive relation used in the numerical simulation, and illustrates several bond-slip constitutive relations commonly used in geotechnical engineering, and obtain the interface bond-slip curve from experimentally measured strain of the bolt.The variation of shear stress in different positions along the bolt-grout interface can be acquired from experimental tests,and the results provide a comparison for numerical simulation.(3)This thesis analyzes the interfacial bond-slip curve derived from experimental tests, proposes interfacial bilinear traction displacement relationship curve. The relevant parameters of the model in ABAQUS traction-separation criterion are specified. And then the experimental constitutive data were used to get the results of numerical simulation as a supplement by using displacement extension criterion. At the same time, the cohesive model in the application of numerical simulation is briefly introduced. On the basis of the theory, combined with the finite element software ABAQUS, this thesis set up the simulation of the bonding relationship of the zero-thickness adhesive layer between bolt and grout body.(4) Using the proposed numerical model for bolt and grouting body, the failure process of bonding interface of bolt and grouting body is analyzed. The failure process of bonding interface can be divided into 4 stages:elastic, elasticity-plasticity, elastic-plastic-stripping, plasticity-stripping. Using the interface bond-slip model proposed in this paper, the interface bonding shear stress and slippage, and the normal stress of bolt have been theoretically obtained. This thesis theoretically explains the concept of valid bond length. Finally, the numerical simulation results show that the interfacial bond-slip model established in this paper can be in good agreement with the experimental tests. That the theoretical results are consistent with the numerical simulation results further proves the significance of the theoretical derivation of the bolt pull-out process.The tri-linear bond-slip model was used to theoretical derivation for further discussion. It could provide the basis for the follow-up research.