Mixed-mode fracture of construction building materials under impact loading is quite common in civil engineering. The investigation of mixed-mode crack propagation behavior is an essential work for fundamental research and engineering application. A variable angle single cleavage semi-circle (VASCSC) specimen was proposed with which the dynamic fracture test was conducted by using a Split-Hopkinson pressure bar (SHPB). Notably, the mixed-mode crack propagation velocity could be detected by the synchronized crack velocity measuring system. With experimental results, the dynamic initiation stress intensity factors K_I and K_II were calculated by the experimental-numerical method. Additionally, the crack path of mixed-mode I/II fracture can be predicated precisely by using numerical method. Thus, a comprehensive approach of investigation on mixed-mode I/II fracture under impact loading was illustrated in this paper. The study demonstrates that the mixed-mode I/II crack would transform from complicated mode I/II to pure mode I during crack propagation, and several velocity decelerations induced crack deflection. The dynamic initiation fracture toughness of mixed-mode crack was determined by the experimental-numerical method. The VASCSC specimen has a great potential in investigating mixed-mode fracture problems with the SHPB device.

In order to study the dynamic stress distribution and the fracture area of rock around the tunnel under different orientations of blasting disturbance, AUTODYN finite difference method software was used to conduct numerical simulation research. Gauge monitoring points were set around the numerical model of the tunnel to conduct real-time monitoring of the stress distribution, displacement and fracture area of the tunnel. Based on the analysis of the stress wave propagation law, the following conclusions are obtained: (1) under the condition of the same blasting loads, the stress and displacement of the tunnel is relatively small when the blasting disturbance source is located above the roof, i.e., the stress state of the tunnel is relatively stable and the fracture area around the tunnel is minimal; (2) from the uniaxial stress around the tunnel and the tunnel peripheral displacement, it can be seen that the displacement caused by horizontal direction stress of the tunnel is the largest, and the deformation is mainly concentrated above the floor and at the shoulder, while the vertical wall part has almost no deformation; (3) for brittle materials such as rock, the arch-shaped stress-bearing surface is more likely to disperse stress, while the straight wall and flat floor of the tunnel cannot well disperse stress, resulting in uneven stress on the stress-bearing surface, uncoordinated deformation and ultimately, failure.

There are a large number of primary and regenerated defects in the rock mass of deep underground engineering, such as primary joints, regenerated cracks and geological holes. When the cracks are subjected to external loads, especially dynamic loads, the dynamic fracture phenomenon will occur. The uncontrolled propagation of cracks will further aggravate the fragmentation of roadway surrounding rock and reduce its stability. To this end, this article simplifies geological fractures into a prefabricated crack and anchor bolt drilling into a single circular hole, thus constructing three types of single crack single hole board experimental configurations (SCSH) with horizontal, vertical, and single hole size variations. The Split Hopkinson Pressure Bar test system (SHPB) is used to explore the influence of single hole on the dynamic fracture behavior of cracks under dynamic load. The effect of physical experiment is verified by the explicit dynamic software AUTODYN, and its influence mechanism is further explored. The results show: (1) as the distance between the circular hole and the tip of the pre-crack increases along the crack direction and propagates to the vicinity of the circular hole, the propagation path tends to the hole; (2) as the increase of vertical distance between hole and pre-crack, the guiding stress field at the tip of the propagating crack and the guiding effect of the hole on the crack are both gradually decrease; (3) with the diameter increase of the hole, which presents a significant guiding phenomenon for the crack dynamic propagation, however, when the hole diameter is less than a certain value, it will have no guiding effect on crack propagation. The research results of this paper can provide strong theoretical support for the corresponding prevention and control measures to ensure the stability of roadway surrounding rock in underground impact pressure mines.

In the process of engineering rock blasting operations, quarrying, and tunnel excavation, explosives are usually detonated in different sequences to achieve the desired fragmentation effect. In this paper, circular PMMA samples with cracks and holes are used to study the model I crack propagation behavior in tunnel blasting sections with empty holes by blasting tests. The distance between the two holes is designed to be within the range of 10 mm to 30 mm. The numerical software AUTODYN codes are used to study the influence of holes on the initiation, propagation behavior of cracks, and the change in the surrounding stress field. The results indicate that: (a) the blasting stress waves diffract and reflect at the edges of the holes and superimpose in the area between adjacent holes, forming a pressure zone, and within a certain distribution range, the more dispersed the distribution of two holes, the more the propagation speed of stress waves decreases; (b) the presence of holes reduces the strength value at the crack tip, and the strength decreases as the distance between the holes increases. The influence of the holes on the stress field at the proximal crack tip is more significant than that of the distal crack tip; (c) the presence of holes increases the difficulty of crack initiation, and the stress intensity factor at crack initiation is basically proportional to the distance between holes.

In rock blasting for engineering applications—such as quarrying and tunnel construction—blasting is often detonated in carefully timed sequences to optimize rock fragmentation. This study examines Model I crack propagation in tunnel blasting sections with empty holes using circular PMMA (Polymethyl Methacrylate) samples containing pre-made initial cracks and empty holes. The distance between holes was varied from 10 mm to 30 mm. Using AUTODYN V18.0 numerical simulation software, how these holes affect crack initiation, propagation, and the surrounding stress field were analyzed. Key findings include the following: (a) Blasting stress waves diffract and reflect off empty hole edges, creating overlapping pressure zones between adjacent empty holes. Within a critical range of the empty hole distance, wider hole distance leads to slower stress wave propagation due to increased dispersion. (b) The empty holes weaken the stress concentration at crack tips, with greater distance further reducing peak strength. Proximal crack tips experience more pronounced stress field alterations than distal ones. (c) Holes hinder crack initiation, with the required stress intensity factor rising in near-linear proportion to hole separation distance.