| Rockbolt support system is a common support technology in coal mine roadway,and its stability and durability are the key to evaluating the support reliability.At present,there is no clear understanding of the influence of surrounding rock strength and cyclic disturbance load induced by mining on the bolt support system.Therefore,this paper adopts the method of indoor pull-out test and theoretical analysis to explore the influence of surrounding rock strength and cyclic disturbance load on the mechanical response characteristics of bolt anchorage bonding interface,in order to improve the understanding of load transfer mechanism of anchorage system in deep complex environment.The main work and conclusions are as following:(1)Influence of surrounding rock strength on mechanical response characteristics of anchorage bonding interface under tensile load.The strength of surrounding rock controls the failure mode of anchorage bonding interface during pulling out.The higher the strength is,the more conducive it is to inhibit the derivation and propagation of radial cracks,and the higher the bearing capacity of anchorage body is.According to the characteristics of normalized bond stress-slip curve,the pull-out process can be divided into four stages:shear,dilatancy slip,softening slip and residual slip.A four-linear constitutive model is constructed to characterize the local bond-slip characteristics of anchor bolts.The model is based on three characteristic control points:initial slip point,peak strength point and residual slip point,and the control points are independent of the diameter of anchor bolts.(2)Characterization of damage evolution of anchorage bond interface based on acoustic emission characteristic parameters and preliminary study of instability slip warning.The evolution law of acoustic emission characteristic parameters of anchorage bonding interface during pull-out process is highly consistent with the slip characteristics of the bonding interface,which can be used as an index to evaluate the slip damage state of bonding interface.The minimum value of acoustic emission b value coincides with the formation of macroscopic cracks at the anchorage bonding interface,so the b value of sharp decline can be used as an early warning index before failure.The idealized bond interface model was constructed.Combined with the damage mechanics theory,the damage evolution of the anchorage bond interface in the pull-out process was quantitatively characterized.It was found that the damage amount when the bond strength reached the peak was independent of the bolt diameter,which further verified the rationality of the theoretical model.(3)Damage slips and fatigues characteristics of anchorage bond interface under cyclic disturbance load.In the case of no fatigue failure,compared with the static pull-out characteristic parameters,the influence of pre-applied cyclic disturbance load on the characteristic bond strength is not obvious.The slip displacement values of initial slip and peak bond strength increase,while the slip displacement values of residual bond strength decrease.The residual slip displacement of bond interface can characterize the development of damage under cyclic disturbance load.Based on this,the prediction equation of fatigue life of anchorage bond interface is proposed,which shows that the fatigue threshold should be above 0.75 ?_u.In this paper,through experimental and theoretical analysis,some new understandings of the damage and slip evolution law of bolt anchorage bonding interface are obtained,which can provide experimental basis for further laboratory tests and numerical simulation studies,and help to promote the design of roadway support in deep complex environments from experience to science. |
PDF Full Text Request