| In order to reveal failure mechanism of fully bonded bolts,this dissertation discussed the main factors which determine durability of fully bonded bolts by theoretical analysis,laboratorial tests,and engineering field verification.A series of researches were subsequently carried out,including microcosmic mechanism of bearing strength restoration in rock/coal,serial decoupling of bonding interface and bonding failure caused by strata separation,reliability test and implementation of prestressed fully bonded bolts,failure mechanism of bolts bonded by segmented steel tube,and durability evaluation of fully bonded bolts suffering cyclic load.Finally,a brief outlooking regarding development of fully bonded bolts in the future was raised.The main conclusions are listed as below.(1)A new type of grouting resin was proposed to implement fully bonded bolting system,and post-peak strength restoration tests on coal and sandstone were conducted based on this kind of bonding material.Relevant results indicated that the proposed grouting resin had certain superiorities in reinforcing cracked coal/sandstone,and corresponding specific implementing process was eventually put forward.Mechanism for failure occurring along resin-rock interface of a bolting system was investigated,thus the serial decoupling process was raised.Theoretical study regarding distribution of interfacial shear stress and axial stress under different bonding states was conducted,and the mechanism for sudden drop of bolting force was discussed from a perspective of bonding states alteration.(2)Pertinent research on separation of layered strata indicated that elastic state of bonding interface corresponded to a critical separation width.Below the width,shear stress distribution was insensitive to the exact locations of separation along the bolting system,and the stability could be guaranteed.Beyond the width,bonding force bilateral the separation would be altered and this alteration was fairly sensitive to locations hereinbefore mentioned.Stability of bolting system suffered dramatically when separation located around embedded end,whereas it was negligibly impacted when the separation located near rock surface.Reasonability of shear stress distribution bilateral the separation was calibrated at last by laboratorial test.(3)A new type of cement-based anchoring bag was proposed to implement prestressed fully bonded bolting system.Pullout tests proved that this system was much more stable and stronger than traditional end-encapsulated resin bonded bolting system.AE tests indicated that increase of pretension force brought decrease of total damage events,and events distribution tended to migrate to bolt rod itself and embedded direction.What determined the bearing property of bolting system under high pretension force was tensile strength of bolt.Relevant laboratorial results were generalized to Datong coal mine in Qinghai province,which turned out as a big success and brought significant effects considering controlling effects of surrounding rock.(4)In order to simulate failure characteristics of fully bonded bolt installed in strata with different thicknesses,segmented steel tubes were adopted and bonded together end by end to form a combined steel tube,then their separation mechanism was analyzed by pullout test.It was acknowledged in the end that failure forms,fluctuation properties,specific amount for pullout load and displacement were closely related to the length of the last segmented steel tube.Moreover,theoretical model for stress distribution inner the steel tube was also built.(5)Dynamic response properties of fully bonded bolts under cyclic load were studied,and reasonable stress distribution inner steel tube was proved by experiment.It found that bolting system also had deformation-memory and rheological properties,however,hysteresis loop similar to rock response under cyclic loading was rarely observed.Failure forms and anchoring configurations were closely related to properties of cyclic load. |
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