Mechanical characterization and dynamic fracture behavior of twin straight-wall-top-arch tunnels under impact loading

This research aims to investigate the effect of external dynamic loads such as blasting, drilling, and mechanical vibrations on the stability of twin straight-wall-top-arch (TSWTA) tunnels. Dynamic impact tests on TSWTA tunnel specimens are carried out by employing the split Hopkinson pressure bar (SHPB) device. The dynamic mechanical characteristics and energy evolution law of the specimens are also methodically explored. In addition, the strain evolution laws and failure modes of TSWTA tunnel specimens are analyzed based on the DIC technique. The results indicate that the presence of TSWTA tunnels weakens the dynamic compressive strength of the rock, and such a weakening effect becomes more pronounced as the spacing between the twin tunnels increases. As the spacing of the TSWTA tunnel specimens increases, the dissipated energy density index of the specimens tends to decrease, indicating a gradual decrease in the degree of specimen failure. The connection regions between the inner vaults of the TSWTA tunnels and the connection regions between their inner bottom are the first to exhibit strain concentration and cracking. As the spacing of the TSWTA tunnels increases, the crack initiation time and propagation rate gradually decrease. Additionally, the interconnected cracks between the TSWTA tunnels result in the loosening and failure of the central rock pillar. With increasing spacing between the TSWTA tunnels, both the degree of failure and the displacement of the central rock pillar gradually decrease. Furthermore, the angle β between the primary tensile crack and the horizontal direction gradually decreases.