## 1 Introduction
Thus, the application of CT scanning technology plays an essential role in understanding the three-dimensional macroscopic fracture characteristics of rock. Additionally, the three-dimensional rock fracture mechanism under blasting loading requires further study and analysis from a microscopic perspective. In recent years, many researchers have utilized scanning electron microscopy (SEM) and other testing instruments to investigate the relationship between the microscopic fracture and macroscopic failure of rock under various loading conditions. Among them, [PERSON] et al. [13] were the first to use SEM to study the failure characteristics of rock fracture surfaces under different loading conditions. [PERSON] et al. [14] used SEM to examine the microstructure and mineral composition of shallow rocks from different geological formations, and analyzed their effects on macroscopic mechanical properties. [PERSON] et al. [15] utilized SEM to analyze the fracture surface morphology of blast-induced cracks in marble under slit charge blasting loading, exploring the directional fracture mechanism of rock under dynamic loads from a microscopic perspective. [PERSON] et al. [16] studied the microscopic morphological characteristics of rock at various locations during blasting using SEM, obtaining the evolution process of internal crack propagation and fracture patterns in blasted rock. It can be seen that the research on the mechanism of blast-induced crack propagation in rock under deep high in situ stress conditions has become relatively advanced. However, the related studies mainly focus on the independent propagation of single or limited numbers of cracks. Studies on the distribution characteristics of crack networks and the damage properties under high in situ stress conditions are still relatively limited, especially in terms of experimental research on three-dimensional rock blasting. CT, SEM, and other testing technologies have been widely applied in analyzing rock blasting damage and fracture patterns. Applying these to the experimental analyses of blasting mechanisms in high in situ stress rock masses can facilitate a clearer understanding of the effects of in situ stress on rock blasting damage and fracture patterns. Based on this, this paper designs a coupled loading device capable of applying both blast-induced stress and in situ stress to three-dimensional rock specimens, simulating model experiments of rock blasting under varying in situ stress conditions. The study conducts a segmental analysis of sandstone, dividing it into stemming, charge, and bottom segments, and investigates the crack propagation and failure modes of sandstone under different in situ stress conditions from macroscopic, mesoscopic, and microscopic perspectives. At the macroscopic level, CT scanning and three-dimensional reconstruction technologies are used to obtain three-dimensional damage images of sandstone cracks under varying in situ stress conditions, providing qualitative insights into crack propagation. At the mesoscopic level, CT scanning combined with multifractal methods is employed to study the relative damage of different segments of sandstone under different stress conditions, yielding quantitative results on the damage patterns of the sandstone. At the microscopic level, scanning electron microscopy (SEM) is applied to examine the failure modes of sandstone under different in situ stress conditions, further revealing the microstructural effects of blasting.