Research On Mechanical Behavior Of Prestressed Full-length Anchorage System And Anchorage Anti-cracking Mechanism

When end anchors are used for roadway support in the coal mine,there are a large number of anchor failures,especially in a deep well with the fractured surrounding rock.The problem of insufficient adaptability under the conditions of large deformation of soft rock in deep coal mines has emerged.Implementing full-length anchorage is an effective means of solving this problem.However,full-length anchoring still does not completely prevent anchor failure from occurring.To reveal the debonding failure mechanism of the full-length anchorage system and the anchoring and anti-cracking effect on the jointed rock body.To achieve the purpose of constructing high-quality anchor solids.This dissertation adopted a combination of field research,theoretical analysis,laboratory experiments,numerical simulations,and engineering practice.The debonding failure process,load-displacement characteristics,anchor solid damage evolution law and crack expansion of jointed rock,and the effect of anchor reinforcement and anti-crack of full-length anchor bolts were investigated.The main research contents and conclusions are as follows:(1)Prefabricated cross fissured rock specimens were designed and fabricated under four geometrical parameters: length of rock bridge,the angle between primary fissure and axial load,the angle between rock bridge,and primary fissure,and angle between primary and secondary fissures.The effects of geometric parameters of the joints on the rock mass crack initiation,propagation,coalescence mode,crack initiation strength and coalescence strength were analyzed.The experiments of crack extension based on the prefabricated cross-fractured rock were carried out.The GPGPU parallelized 2D Y-HFDEM IDE code was applied to simulate the damage process of the jointed rock mass.The transition of rock mass deformation from continuous to discontinuous media was realized.Experimental and simulation results were obtained the damage caused by mixed tensile-shear cracks sprouting and expanding at the tip of the main fissure was obtained to be dominant in the final damage to the rock.It is the main control crack that causes the rock mass to lose its bearing capacity.Guides controlling the deformation of jointed rock masses.(2)The mechanical analysis model of the bolt-anchoring agent interface was constructed.The bolt pull-out sliding leading to anchoring agent ring crack expansion and the change of circumferential pressure at the bolt-anchoring agent interface and anchoring agent-rock interfaces with bolt sliding was analyzed.The locations of the maximum axial force and shear stress were deduced.The failure mechanism of the boltanchoring agent interface by cyclic diffusion was revealed.Full-length anchorage system loading experiments were carried out under the condition that the tensile strength of the surrounding rock was greater than the tensile strength of the anchoring.Combined with bolt strain analysis and anchor solid acoustic emission monitoring.The load transfer mechanism of the full-length anchorage system,the load-bearing characteristics of the bolt,and the stress distribution characteristics were analyzed.The debonding failure behavior of the bolt-anchor agent interface was also analyzed from the acoustic emission response characteristics,the anchor solid damage evolution law,and the spatial evolution process of pull-out debonding.The correspondence between the way the pullout anchor force acts and the anchor agent ring integrity state is obtained for the four stages of the anchorage failure process.The cumulative damage of anchor solids was mainly occurred in the elastic deformation phase of bolts(39 %)using acoustic emission monitoring.Reducing the amount of damage to anchor solids in the elastic deformation stage of bolts is conducive to improving anchorage quality.(3)Anchor solid mechanical response experiments with 5 factors and 3 levels of bolt diameter,anchorage length,surrounding rock strength,surrounding pressure and preload were carried out.The effects of bolt diameter,anchorage length,surrounding rock strength,surrounding pressure,and preload on pullout load,axial stress and shear stress distribution,anchor solid acoustic emission response law and evolution characteristics of damage variables were investigated.It is revealed that the reason for the higher anchorage quality in full-length anchorage compared with end anchorage is the reduced amount of damage produced by the anchor solid in the elastic deformation phase of the bolt after full-length anchorage.The amount of damage in the pull-out damage phase increased.The full-length anchorage improves the safety of the bolt before yielding load.And several key ways to construct high quality anchor solids were proposed.(4)A series of 5-factor,3-level experiments were designed on the anchoring and crack-stopping effect of jointed rock with or without bolt,anchor length,preload,anchor location,and anchor number.The combination of acoustic emission damage monitoring and digital image correlation(DIC)monitoring.The effects of no bolt,anchorage length,preload force,anchorage position,and bolt quantity on the changes of mechanical parameters,acoustic emission characteristics,damage evolution law,deformation field evolution characteristics and crack expansion of anchor solids were analyzed.The suppression effect of bolts on the master crack expansion under different working conditions was obtained.The anchoring and anti-cracking effect of bolts on the jointed rock mass were revealed.(5)The way to reduce the damage of anchor solid was proposed,and the purpose of constructing high-quality anchor solid was realized and applied to the field engineering practice.Using comprehensive testing and analysis of roadway envelope deformation monitoring,anchor cable axial force monitoring,and borehole peephole analysis,the results show that: The full-length anchorage can control the deformation of the surrounding rock and increase the pull-out anchorage force in time,effectively controlling the deformation of the surrounding rock and reducing the anchorage failure phenomenon.The increase in cable diameter suppressed the damage of anchor solids in the elastic deformation stage of the cable.The control of the initial deformation and fracture expansion of the surrounding rock was enhanced by increasing the pre-load force.The combination of short and long cables was optimized to build a stable anchorage layer.It shows that the optimized support effect is significantly improved.It shows that the pre-stressed full-length anchorage technology has significant advantages in controlling roadway deformation under complex and difficult conditions.There are 119 figures,14 tables,and 197 references in this dissertation.