Cumulative Damage Feature Analysis Of Fully Grouted Gfrp Rock Bolts Under The Blasting Dynamic Loads

Aiming at the cumulative damage and failure problem of fully grouted GFRP bolts under blasting dynamic loads,the paper first reveals the cumulative damage process of the bolt support system under blasting dynamic loads based on the stress principle of the bolt under blasting dynamic loads,and determines the failure forms and main influencing factors of the GFRP bolt.Then,taking the maximum axial stress at the end of the rod and the debonding length of the anchor interface as the damage variables,combined with Miner’s linear cumulative damage theory,the paper establishes a cumulative damage calculation model for GFRP bolt.At the same time,the paper uses FLAC^3Dsoftware to establish a dynamic load bearing model of full-length mortar anchor bolt,and based on the support parameters of GFRP bolt and the measured data of blasting vibration in Jinchuan No.3 Mining Area,carries out theoretical research and numerical analysis on the stress and cumulative damage characteristics of fully grouted GFRP bolt under blasting dynamic loads,and compares the research results with metal bolt.Finally,the feasibility of GFRP bolt support under dynamic blasting load is determined through the analysis of the effect of GFRP bolt support and field tests in Jinchuan No.3 Mining Area.The main research results of this paper are as follows:（1）Under dynamic blasting load,the axial stress of the fully anchored GFRP bolt reaches its maximum at the hole opening,and then exponentially attenuates to zero along the axial direction of the rod body,with a more concentrated stress distribution than metal bolt.The shear stress at both interfaces rapidly increases to a peak value along the axial direction of the rod and then decreases to zero.After that,the interface with relatively weak bonding performance first undergoes debonding failure,and the shear stress at the debonding position decreases to the residual bonding strength,while the peak shear stress shifts to the bottom of the hole.The interfacial shear stress of GFRP bolt is more concentrated than metal bolt,and the peak position is more prominent.（2）The maximum axial stress of GFRP bolt increases linearly with the increase of dynamic load strength and decreases with the increase of surrounding rock or mortar strength.Changing the dynamic load strength does not change the failure mode of the anchoring interface,and debonding failure always occurs at interfaces with relatively weak bonding properties.The greater the dynamic load strength,the greater the interfacial debonding length and shear stress distribution range,and the closer the peak shear stress position is to the hole bottom,while the peak shear stress position of the undamaged interface will also shift towards the hole bottom.The greater the strength of surrounding rock or the smaller the strength of mortar,the more likely the shear failure occurs at the rod-mortar interface,conversely,the more likely the shear failure occurs at the mortar-rock interface.（3）The cumulative damage rate of GFRP bolt rod body continues to increase with the number of blasting times,but the growth rate is relatively slow,while the cumulative damage rate of anchorage interface increases rapidly with the number of blasting times,showing an exponential growth.The cumulative damage characteristics of GFRP bolt rod are to some extent opposite to those of metal bolt,and their explosion resistance performance is worse than that of metal bolt.The cumulative damage characteristics of the anchoring interface are basically consistent with those of metal bolt,the interfaces begin to debond from the orifice,and the debond length increases exponentially with the number of dynamic loads.（4）With the increase of dynamic load strength,the maximum stress times before failure of GFRP bolt rod and the anchoring interface decrease exponentially,and exhibit a two-stage characteristic of first rapid decline and then slow decline.The greater the strength of surrounding rock or mortar,the smaller the damage caused by a single blasting dynamic load to the rod and interface,and the smaller the cumulative damage speed of the rod and interface.With the increase of interfacial bonding strength,the cumulative damage velocity at the interface decreases significantly.（5）The effect analysis and field test of GFRP bolt support under blasting dynamic load show that the validity period of the optimized GFRP bolt support is obviously improved,and no obvious bolt failure occurs.On the whole,the stress of the bolt does not exceed the tensile strength of the GFRP bolt itself.The stability of the ore and rock in the support area meets the requirements of normal production on site.It is feasible to use GFRP bolt support under blasting dynamic load conditions.