Study on fracture characteristics of surrounding rock of twin tunnels under various crack inclination and location conditions

In some practical projects, two neighboring tunnels are often constructed in natural rock bodies that have a significant number of fractures with unpredictable inclination angles and locations. To study dynamic fracture characteristics of the surrounding rock mass of the twin tunnels containing a crack with different crack inclinations and crack locations, an experimental model of a cracked twin tunnel was designed and proposed, dynamic experimental analyses were carried out by using a traditional split Hopkinson pressure bar (SHPB) device and digital image correlation (DIC) method, followed by simulation conducted by using LS-DYNA code. The findings indicate that the spandrels and corners of the twin tunnels nearest the pre-cracks are more vulnerable to failure under dynamic loads, resulting in tunnels joining the ends of the pre-cracks. With various crack inclinations and crack locations, the initial cracks are typically produced at the roof and floor of the tunnel, as well as at the points of the pre-cracks. The specimen's kind of crack and its emergence site are connected. Crack inclination and location have little influence on the maximum displacement value in the twin tunnels. The study's findings could offer a fresh theoretical direction for evaluating the stability of twin tunnels when there are numerous joints and flaws.