Study On Synergistic Load-Bearing Mechanism Of Fully Bonded Bolts And Surrounding Rocks

Bonded bolts have become important means for surrounding rock stability control because of the significant effect of anchorage,but it is still lack of unified understanding about the anchor mechanism.Existing studies mostly treat bolts and surrounding rocks as separate individuals for discuss,ignoring the essential characteristic that bolts and surrounding rocks are a unified whole.In this thesis,fully bonded bolts are used as the research carrier,and bolts and surrounding rocks are taken as unified object.The physical simulation and numerical simulation are used to analyze the stress characteristics,deformation and energy evolution of the anchor solid with different anchorage variables.Based on the viewpoint of Synergetics,the evaluation model of anchorage synergistic effect is established from the angle of energy to explore the synergistic load-bearing mechanism of fully bonded bolts and surrounding rocks.Main research results are as follows:(1)Based on the similarity criterions,different materials are used to simulate soft rocks and hard rocks.The ratio of the matarials are determined by basic mechanical tests and the model samples are prepared.The physical simulation system is designed according to the research contents,with the use of advanced digital photography deformation measurement technology and dynamic FBG stress measurement technology,the loading and data acquisition functions of the anchorage models are realized.(2)Through physical simulation tests,the influence rules of load-bearing capacity of anchorage bodies under different surrounding rocks conditions and bolts layouts are obtained.The difference of mechanical properties between soft rocks and hard rocks is obvious,the loadbearing capacity and energy storage capacity of soft rocks are less than that of hard rocks.The peak strength,elastic modulus and strain energy reserves of anchored surrounding rocks are improved,which shows positive synergistic effect,especially in soft rocks.Excessive bolt layout density will promote the development of cracks,and the synergistic effect between anchor and surrounding rocks will be reduced,whitch is not conducive to the load-bearing of surrounding rocks.(3)Through the monitoring of axial force of bolts,it is found that the axial force of soft rocks bolts rises early and the rising of the axial force of the hard rocks bolts is lagging behind.It is shown that the load-bearing capacity of bolts is different under different surrounding rocks conditions.It is found that the soft rocks show obvious plastic damage characteristics while brittle fracture characteristics of hard rocks through the digital photography,and displacements of different surrounding rocks are all convergent after anchoring.(4)The influences of bolt layouts,bolt length,bolt materials and preload on the load-bearing capacity of the anchorage bodies are obtained by PFC3 D numerical simulation.The layouts and preload have significant influences on the synergistic effect between anchor and surrounding rocks.The effects of anchorage on soft rocks are more prominent than that of hard rocks,and the soft rocks are more sensitive to the change of anchorage variables.(5)By improving the stress state of surrounding rocks,the anchorage can improve the energy storage capacity of the surrounding rocks before the peak strength,and control the release of energy after the peak strength,so that the surrounding rocks form a good self-bearing structure and has a wider adaptability.The energy storage capacity of soft rocks are poor,and the mechanical properties of surrounding rocks before the peak strength are ameliorated obviously by anchoring.The utilization rate of hard rocks before the peak strength is low,and the strain softening characteristics of surrounding rocks after peak strength are obviously improved by anchoring.