Study on Mechanical Properties of Shotcrete Arch Frames in Tunnel Engineering Considering Blasting Excavation Effect at Early Age

Steel arches and shotcrete systems are the most commonly used forms of initial support structures in underground tunnel engineering. Blasting and excavating in tunnels constructed using the drill-and-blast method affect the synergy between the early-age concrete and the steel arch. Research on the performance of commonly used grid steel frames and I-steel frames in tunnel support systems under blasting vibration conducted to date is not sufficient. In this paper, an experimental instrument was developed that can apply displacement and impact loads on concrete at an early age to simulate the stress situation of a steel frame during tunnel blasting excavation, and four groups of steel-grid frame and I-frame experiments were carried out. A numerical simulation of twelve schemes was launched based on ABAQUS, considering the effects of arch curvature and the time of impact load. Results: (1) The synergistic action between the steel frame and concrete has a time effect, and the damage between rebar and concrete caused by the blasting action decreases with the age of the concrete. (2) After the impact load, the ultimate bearing capacity of the two types of steel frame decreases by 25% and 15.5%, respectively, and the bearing capacity of the I-steel concrete arch is higher than that of the grid concrete arch, but the I-steel concrete arch is greatly affected by the vibration load. (3) The impact load and curvature of the steel arch have an impact on the synergy between the steel frame and concrete, while the supporting performance of the I-frame concrete arch is more significantly decreased by the effect of blasting excavation.