Study On Bearing Characteristic Of Pre-stressed Bonded Rockbolt In Jointed Rockmass

The jointed rockmass is complex rockmass which is often encountered in engineering project.Rock joints destroy the integrity and continuity of rockmass,weakening the strength.Under the external force,rock joint are prone to open and slip.And the anchoring mechanism of jointed rockmass has not been fully understood.There needs to be more studies on the stress distribution law and the bearing capacity of rockbolt in jointed rockmass,the interaction between rockbolt,epoxy and surrounding rock.Therefore,it is very important to study the bearing capacity of pre-stressed bonded rockbolt in jointed rockmass,which is of great significance to improve the stability of jointed rockmass.In this paper,the methods of theoretical analysis,physical simulation and numerical simulation,field test and industrial test are used to study the stress distribution along the embedded direction under different anchoring forms of rockbolt in jointed rockmass.The main work of this paper is as follows:(1)The transfer path of rockbolt loading at different stages is analyzed.Based on elastic theory,the mechanical model of rockbolt in the pre-stressed stage and the expanding deformation stage of jointed rockmass is established,the formulas of axial stress in the blot and the shear stress at the bolt-epoxy interface along the embedded direction is obtained.The stress distribution curve of rockbolt with different anchoring forms is deduced by using the specific parameters to verify the theoretical model.(2)The solid element model of pre-stressed bonded rockbolt in jointed rockmass is established by using FLAC3 d.The parameters of selected material are obtained by laboratory pull-out test of rockbolt.Based on the accuracy of material parameters in the numerical model,the stress characteristic of point anchoring bolt,extended anchoring bolt and fully anchoring bolt is analyzed under the pre-stressed stage,the expanding deformation stage of jointed rockmass,the sliding deformation stage of jointed rockmass.(3)The pre-stress distribution law of bolt shows that pre-stressing force of fully anchoring bolt along the embedded direction is hard to diffuse and stress concentration of bolt end is easy to be caused.The compressive stress zone of rockmass under extended anchoring and point anchoring state is pear-shaped and the compressive stress diffuses far away.The expanding deformation stage of jointed rockmass: point anchoring bolt has the lowest sensitivity to joints expanding,and it cannot control the strata separation in time.The extended anchoring bolt is most sensitive to joints expanding,it can control the strata separation in time,and improve the support rigidity.The sliding deformation stage of jointed rockmass: point anchoring bolt cannot prevent the strata sliding along the joint plane in time,the bolt has force reaction only after the shear displacement reaches a certain value,the support rigidity is low.Extended anchoring and fully anchoring bolt are very sensitive to the shear displacement and they can control the shear sliding of jointed rockmass early.Compared with point anchoring bolt,extended anchoring and fully anchoring bolt can alleviate the stress concentration in jointed rockmass and control the shear sliding better.The incline of bolt installation acts better than the vertical of bolt installation in a similar way.(4)Through analyzing and summarizing the research results,the key control technology of rockbolt support in jointed rockmass is put forward.The bolt stress distribution law along the embedded direction is analyzed with the measured data of dynamometer bolt in coalmine.A reasonable support program of 81303 tail entry in the First Mine is put forward,and successfully applied to engineering practice.