Research On Interfacial Response Of Fully Bonded Layer-nailing Anchoring Body And Its Reinforcing Mechanism On Rock Mass

The roof of coal mine roadways in China are mostly thin-layered structures,which are commonly supported by prestressed bolts nailing different rock layers in the form of end bonding or lengthened bonding.As coal mining goes to the deep,the interlayer discontinuous deformation and layer separation of the layered roof roadway is intensified,while the end bonded or lengthened bonded bolts have limitations in perceiving the deformation of the nailed rock strata,resulting in a significant reduction of their support effectiveness,which causes safety accidents.Recent engineering applications have shown that fully bonding technology provides a new way to solve this deep engineering problem.The bearing mechanism and support effectiveness of fully bonded bolts are closely related to the mechanical properties of the nailed rock strata,so it is of great scientific significance and engineering value to systematically study the mechanical properties of fully bonded layer-nailing anchorage body.The thesis adopts a combination of laboratory tests,numerical simulations and engineering practice to investigate the interfacial response of fully bonded layer-nailing anchoring body and its reinforcing mechanism on rock mass,and the following main research conclusions are obtained:(1)The evolution of the bearing characteristics of fully bonded layer-nailing anchorage body under the influence of multiple factors was revealed.Anchorage specimens were prepared for laboratory pull-out tests to compare the bearing performance of anchorage body under different mechanical properties and structures of the nailed rock strata,and the amplification effect of the confining pressure on the pullout load capacity of anchorage body and its engineering significance were explained.The long-term loading experimental system was used to study the deterioration of anchorage body pull-out load capacity under long-term loading.The study showed that the strength of the nailed rock strata and the bearing capacity of the anchorage body were positively correlated,and the long-term loading under low confining pressure reduces the bearing capacity of the anchorage body by 17.0%-52.9%.And the enhancement of the confining pressure can effectively strengthen and maintain the bearing capacity of the anchorage body.(2)The interfacial response characteristics of fully bonded layer-nailing anchorage body under pull-out load were elucidated.With force measuring bolts and acoustic emission system,the distribution of axial force and interface shear stress and the fracture evolution process of anchorage body were obtained.The migration evolution process of the bearing core of fully bonded layer-nailing anchorage body interface from shallow to deep was revealed.The concept of critical bearing stratum in nailed rock strata was proposed.It is shown that the critical bearing stratum was the rock stratum where the peak shear stress of the interface was located when the anchorage body reaches the pull-out load capacity,that is,the rock stratum that can provide the highest shear strength of the second interface.The load blocking effect of the critical bearing stratum and its location on the response of the anchorage interface was analyzed.(3)The mechanical properties and sequential fracture evolution of layered rock mass were studied.Combined with laboratory tests and PFC3 D numerical simulation,the mechanical properties of layered rock mass with different proportions of soft and hard rock were studied.And the pre-peak damage of the layered rock mass was quantitatively evaluated with acoustic emission system.The internal inhomogeneous bearing phenomenon was analyzed.It was shown that the mechanical properties of layered rock masses were between those of homogeneous soft rock and homogeneous hard rock,and decreased slowly and then rapidly with the increase of the proportion of soft rock.The damage of the soft rock in the layered rock mass preceded that of the hard rock,and the high stress environment intensified the layer separation.(4)The reinforcement mechanism of fully bonded layer-nailing anchored rock mass was investigated.The effect of different bonding methods and support strengths on the mechanical properties of the layerd rock mass was investigated through laboratory tests,and the exponential decay function strengthening correspondence between the anchoring parameters and the mechanical properties of the nailed rock mass was established.The supporting effects of fully bonded bolts and end bonded bolts on layered rock masses were compared in terms of strengthening effect and damage control.By PFC3 D simulation,the mechanical properties and mesoscopic crack propagation process of the fully bonded layer-nailing anchored rock mass under different stress environments were studied.It was found that fully bonded bolts are significantly more effective than end bonded bolts in supporting layered rock mass,and the strengthening effect of fully bonded layer-nailing anchored rock mass was about twice that of end bonded layer-nailing anchored rock mass under the same conditions.(5)The support principle of deep high stress layered roof roadway was proposed,and the engineering verification was carried out in Wuju coal mine in Pingliang,Gansu.The controlling difficulties of deep high-stress layered soft rock roof roadway in Wuju coal mine were analyzed,the supporting technology of multi-level layer-nailing thick anchored rock beam based on prestressed fully bonding was proposed.The support scheme of railway inclined shaft in Wuju coal mine was designed.After the implementation of the new scheme,the integrity of the surrounding rock on the surface of the roadway was good,the layer separation of layered soft roof was eliminated,which provided valuable experience for the support design of the same type of roadway.There are 161 figures,26 tables and 172 references in this dissertation.