Study On Bearing Properties And Failure Modes Of Anchors Under Cyclic Load

Based on the evaluation of the stability of bolt anchorage system under cyclic perturbation loads,the dissertation studies the bearing performance and anchorage failure mode of anchor under cyclic load by theoretical analysis,push-in experiments,and acoustic emission positioning.In the research,it mainly analyzes the bearing capacity of different surrounding rock anchors under different forms of cyclic loads.At the same time,it analyzes the internal damage and failure modes of the anchor.The main conclusions are listed as follows:(1)The distribution of shear force on the interface and the axial force on the anchor are analyzed.The distribution function of the shear force on the anchorage interface and the axial force during the loading process is established.The influence of cyclic loading on the shear force on the interface between the anchor layer and the surrounding rock and the distribution of the axial force is analyzed.(2)The change of the bearing capacity of anchors in soft surrounding rock under the dynamic load was studied.For anchors in the soft surrounding rock,when the cycle frequency is constant,the ultimate bearing capacity of the anchor increases with the increase of the cyclic amplitude,but the addition amount decreases,and the carrying capacity after the disturbance decrease with the increase of the cycle amplitude.When the cyclic amplitude is constant,the ultimate bearing capacity of the anchor increases with the increase of the cyclic loading frequency,but the increasing amplitude is gradually reduced.The load carrying capacity of the anchor is affected less by the low-frequency load,and only the frequency of the cyclic load increases to a certain level-10 Hz,the carrying capacity of the anchor after the disturbance rapidly decreases.(3)Under the anchorage condition of medium hard rock,when the cyclic frequency is constant,the low-amplitude loading(40%F)does not affect the ultimate bearing capacity of the anchor,but the bearing capacity of the anchor after cycling disturbance is obviously improved;when the cyclic loading amplitude exceeds a certain level,Ultimate load capacity and carrying capacity after the disturbance decreased.When the cyclic amplitude is constant,the ultimate bearing capacity increases quickly at low frequency(5Hz)loading,but the bearing capacity of the anchor after cyclic disturbance is basically unchanged;when the cyclic frequency increases to 10 Hz,the ultimate bearing capacity of the anchor remains basically unchanged.The bearing capacity of the anchor rapidly declines after cyclicdisturbance.(4)Explore the anchor failure form and internal damage under cyclic disturbance.Under soft rock anchorage conditions,with the increase of cyclic amplitude,the failure modes of anchorage are all damage of surrounding rock,and the extent and density of damage of acoustic emission location also increase.With the increase of the cycle frequency,the failure modes of the anchor are changed from the debonding of the anchoring agent-rock interface to the shear fracture of the rock near the bolt.When the frequency is increased to 10 Hz,he interior of the anchor appears damage-intensive areas.However,under the low-frequency and high-frequency loading,there is damage continuous lines inside the anchor.(5)Under the anchorage condition of medium-hard rock,with the increase of cyclic amplitude,the failure modes of anchorage are changed from the debonding of anchoring agent-rock interface and the shear fracture of rock mass near the bolt to the damage fracture of the surrounding rock.The acoustic emission location indicates the extent of damage-intensive areas also increased accordingly.With the increase of the cyclic frequency,the failure modes of anchorage are changed from the shear failure of the surrounding rock mass near the bolt and the integral fracture of the external rock mass to a single external fracture of the rock mass,and when the cyclic load frequency is increased to 10 Hz,Acoustic emission shows that the number of damage-concentrated areas and the number of damaged continuous lines increased significantly.