Dynamic propagation behavior of cracks emanating from tunnel edges under impact loads

In order to study crack dynamic propagation behavior of cracked tunnels under dynamic loading, a new configuration specimen of a tunnel with single radial crack (TWSRC) emanating from tunnel edge was proposed and by using these specimens, drop weight impacting experiments were conducted in this paper. The study using TWSRC specimens could be directly applied to tunnel engineering, and could guide tunnel designers to enhance tunnel stability. Sandstone was selected to make TWSRC specimens and crack propagation gauges (CPGs) and strain gauges were used to measure crack initiation and propagation time and crack speed. Numerical models were established by using the finite difference code AUTODYN to simulate crack propagation behavior and propagation path. The finite element code ABAQUS was used to calculate dynamic stress intensity factors (SIFs). For cracks propagating with a speed, the dynamic SIFs were obtained by the corresponding stationary crack SIF times a universal function. According to the initiation time and propagation time, the critical SIFs (or fracture toughness) in initiation, propagation and arrest were determined by the experimental-numerical method. The results show that (1) in the process of crack propagation, crack speeds are not a constant, and the cracks may temporarily stopped for a period, and in this study, the maximum arrest period is 227.52 μs; (2) the propagation toughness is related to crack speeds, and the arrest toughness is lower than the initiation toughness.