This study explored the dynamic behaviors and fracturing mechanisms of flawed granite under split‐Hopkinson pressure bar testing, focusing on factors like grain size and flaw dimensions. By means of digital image processing and the discrete element method, Particle Flow Code 2D (PFC^2D) models were constructed based on real granite samples, effectively overcoming the limitations of prior studies that mainly relied on randomized parameters. The results illustrate that the crack distribution of granite is significantly influenced by grain size and flaw dimensions. Tension cracks predominate and mineral boundaries, such as between feldspar and quartz, become primary crack sites. Both flaw length and width critically affect the crack density, distribution, and dynamic strength of granite. Specifically, dynamic strength tends to decrease with the enlargement of flaws and increase with an increase in flaw angles up to 90°.

Investigating dynamic responses and damage modes of tunnels constructed in different geological conditions is of great significance to understand the damage mechanism and put forward mitigation measures. In this paper, large-scale shaking table tests with the similarity ratio of 1:12 were used to study the seismic response (acceleration and spectrum characteristics, hoop strain, dynamic earth pressure, and longitudinal strain) of shallow buried elliptical tunnels motivated by different dynamic loads. Three different conditions of tunnel section were discussed: with shock-absorbing layer (SAL), with fault, and without SAL and fault. Then the slipping and expanding displacement, dynamic stress concentration, and damage modes of the tunnel across the fault fracture zone were studied based on numerical simulations. The research results illustrate that the presence of SAL has slight influences on amplifying the peak acceleration of the excitation motions and controlling the longitudinal strain, but it could effectively mitigate the motion energy and dynamic earth pressure around tunnels; it also demonstrates that the SAL can be utilized as a damping layer to weaken the seismic waves. Additionally, tunnels in the fault fracture zone perform remarkable dynamic response than those in the normal surrounding rock; the largest slipping and expanding displacement of fault often occur at the moment when the acceleration of the excitation motion reaches its high value.