Cumulative damage characteristics of fully grouted GFRP bolts in rock under blasting dynamic loads

In the civil and mining industries, bolts are critical components of support systems, playing a vital role in ensuring their stability. Glass fibre reinforced polymer (GFRP) bolts are widely used because they are corrosion-resistant and cost-effective. However, the damage mechanisms of GFRP bolts under blasting dynamic loads are still unclear, especially compared to metal bolts. This study investigates the cumulative damage of fully grouted GFRP bolts under blasting dynamic loads. The maximum axial stress at the tails of the bolts is defined as the damage variable, based on the failure characteristics of GFRP bolts. By combining this with Miner's cumulative damage theory, a comprehensive theoretical and numerical model is established to calculate cumulative damage. Field data collected from the Jinchuan No. 3 Mining Area, including GFRP bolts parameters and blasting vibration data are used for further analysis of cumulative damage in fully grouted GFRP bolts. Results indicate that with an increasing number of blasts, axial stress increases in all parts of GFRP bolts. The tail exhibits the most significant rise, with stress extending deeper into the anchorage zone. Cumulative damage follows an exponential trend with the number of blasts, although the incremental damage per blast decelerates over time. Higher dynamic load intensities accelerate damage accumulation, leading to an exponential decline in the maximum loading cycles before failure. Additionally, stronger surrounding rock and grout mitigate damage accumulation, with the effect of surrounding rock strength being more pronounced than that of grout. In contrast, the maximum axial stress of metal bolts increases quickly to a certain point and then stabilizes. This shows a clear difference between GFRP and metal bolts. This study presents a new cumulative damage theory that underpins the design of GFRP bolt support systems under blasting conditions, identifies key damage factors, and suggests mitigation measures to enhance system stability.