## 5 Conclusions  
Given the dynamic load effect of mechanical impact and explosive blasting on surrounding rock during the excavation of underground openings in rock engineering, a number of impact tests were carried out using the SHPB testing system on seven groups of prismatic specimens (including one group of intact samples and six groups of rock samples containing holes with different numbers and layouts) in this work to explore the dynamic mechanical properties and failure behavior. In the tests, the influence of hole quantity and hole layout was deeply explored and discussed, and some conclusions could be refined as follows.  
1. A series of tests on rock chemical composition, microstructure and basic physical-mechanical parameters indicate that this kind of rock can be graded as tufaceous-feldspar-quartz sandstone which has a fine-medium sand texture and a blocky structure, and belongs to medium-strength brittle rock.
2. The prismatic specimens applied for dynamic experiments using SHPB device meet the stress uniformity assumption, and the stress waves attenuate when encountering holes. The dynamic compressive strength of the specimens is significantly deteriorated by the opening number and layout. The dynamic deformation process of the samples containing holes under impact loads could be parted into three phases: the elastic deformation phase, plastic deformation phase and the post peak phase. However, no regularity was found in the dynamic elastic modulus and peak strain of the pre-holed samples.
3. The dissipated energy densities and the dynamic compressive strength of several groups of samples showed the same change rule. The size order of the sample fragmentation can be listed as G3 < G2 < G5 < G4 < G7 < G6, which is consistent with the result derived from employing fractal dimensions to describe the rock fragmentation. In addition, the dynamic fracturing process of the sample with openings could be clearly captured with a high-speed camera, and it was found that there are three sorts of cracks, namely spalling cracks, shear cracks and tensile cracks, which formed around the holes during the tests. The samples of groups G2 and G4 suffered from shear-dominated failure, while the samples of groups G3, G5, G6 and G7 presented tensile-shear failure, suggesting that the fracturing behaviors are highly related to the opening configuration.  
Conceptualization, H.W. and Y.J.; methodology, H.W.; validation, [PERSON]; investigation, H.W.; resources, Y.J.; writing--original draft preparation, H.W.; writing--review and editing, Y.J.; supervision, Y.J.; funding acquisition, H.W. All authors have read and agreed to the published version of the manuscript.  
This study was jointly granted by the National Key R&D Program of China (2022 YFC2905600), National Natural Science Foundation of China (52204160), the Natural Science Foundation of Jiangsu Province (BK20210515), the China Postdoctoral Science Foundation (2022 MD713814, 2023T160555) and the Foundation of Hubei Key Laboratory of blasting Engineering (No. BL2021-10). Additionally, the support from the Yunnan Postdoctoral Science Foundation and the \"Double Innovation Plan (JSSCBS20221519)\" of Jiangsu Province are also greatly appreciated.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
Authors thank to [PERSON], [PERSON] and [PERSON] for their contribution to this article.  
Author [PERSON] was employed by the company Yunnan Phosphate Chemical Group Co., Ltd. The remaining author declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.