## 1 Introduction
[15] modeled the fracturing process of the samples with circular, horseshoe-shaped, trapezoidal, rectangular or square holes under biaxial compressive loads, and claimed that their fracture evolution is similar but with different initiation stress and crack strength under identical loading conditions, and the tensile cracks and remote cracks are restricted as the confining pressure rises, which were clearly explained according to the stress distributed near the cavities derived by an improved complex variable method. In addition, other loading methods such as general triaxial loading [16], true triaxial loading [17], Brazilian split tension [18], one-dimensional impact loading [5; 19], one-dimensional static-dynamic loading [20; 21; 22], two-dimensional static and one-dimensional dynamic loading [23; 24; 25; 26] and dynamic Brazilian split tension [27] were employed on samples with one circular, elliptical, horseshoe-shaped or rectangular hole to examine the fracturing behaviors and mechanical properties, providing some insights into the failure characteristics of underground openings under geo-stress. Actually, there is rarely one single hole but multiple holes in rock mass, and holes like air pores in basalt and tunnels in underground rock engineering generally occur in groups. It is evident that performing different loading tests on specimens with two or more holes is of more practical value. For this purpose, numerous efforts have been devoted to studying the crack development and intersection features of samples with more than one opening subjected to various loads. [PERSON] et al. [28] analyzed the strength, deformation and AE properties of rock-like samples with two round holes with various rock bridge inclinations in uniaxial compression, and concluded three failure modes and two deformation stages. Literature [29] conducted a list of axial compression experiments on sandstone samples with two oval holes with different configurations, and discovered six types of cracks and four failure modes. With the aid of DIC measurement, [PERSON] et al. [30]clearly presented the deformation fields and crack coalescence patterns of marble samples with two rectangular openings in axial compression. [PERSON] et al. [31] applied the RFPA code to investigate the intersection mechanisms and failure modes of samples with three or numerous round openings under axial loading, and the numerical outcomes agree well with the laboratory conclusions obtained by [PERSON] et al. [32]. In our previous work [33; 34], we also experimentally investigated the strength, deformation and fracturing responses of sandstone samples with two, three and four inverted-U shaped openings under uniaxial loading, and deemed that the intersection of the tensile cracks, shear cracks and holes leads to failure. [PERSON] et al. [35] studied the crack extension and connection of different concrete specimens with cavities under Brazilian split tension both experimentally and numerically. Moreover, the influence of material type, material heterogeneity and temperature treatment on the fracturing feature was also explored [36; 37; 38]. Since tunnel excavation and stope mining are usually constructed by the drilling and blasting method in hard-rock mines, the surrounding rocks frequently suffer from the dynamic loads. In mining engineering, a large number of tunnels are distributed in various locations underground, and there may be two, three or more parallel tunnels in a certain space. As a result, tunnel stability is affected by dynamic disturbances from surrounding tunnel excavation activities. However, much of the aforementioned literature is based on static tests, and studies are still limited regarding dynamic experiments.