# Study on Mechanism of Static Blasting-Induced Hard Rock Fracture Expansion
## 5 Discussion  
This article explores the mechanical analysis of static cracking agents, elucidating their underlying mechanisms and principles, as well as the dynamics of expansion pressure and rock fracturing. By conducting PFC2D inversion experiments, the feasibility of simulating fractures induced by static cracking agents is demonstrated. The study investigates the internal dynamic effects, crack propagation characteristics, and patterns of expansion pressure development under various aperture sizes, spacing, and confining pressures. This research significantly contributes to enhancing the convenience and timeliness of downhole rock fracturing using explosives. While the existing literature has extensively examined the mechanical mechanisms and crack propagation laws of bulk cracking agents [12; 13; 24; 29; 30], this paper specifically highlights the mechanical principles and mechanisms of rolled cracking agents. Rolled static cracking agents (RSCA), compared to traditional bulk static cracking agents (BSCA), generate higher expansion pressure, leading to improved effectiveness and efficiency, especially in rapidly fracturing hard rocks.  
The experiments on expansion pressure play a crucial role in determining the effectiveness of static fracture agents [14; 15; 18]. The magnitude of expansion pressure determines the speed at which rocks are fractured. Previous studies have primarily focused on the impact of different environmental factors on expansion pressure and the resulting expansion laws [17; 19; 21; 22]. However, this study focuses on investigating the variations in expansion pressure and crack propagation laws based on the morphology of the fracture agents themselves. The aim is to enhance the efficiency of rock fracturing, starting from the very source. In a comparative analysis, when the inner diameter of the steel pipe is the same, the RSCA demonstrates an expansion pressure that is 9.5-12.2% higher than the BSCA. For a 30 mm inner diameter, RSCA and BSCA exhibit expansion pressures of 38.2 MPa and 43.5 MPa, respectively. The peak expansion pressure for BSCA occurs between 240 min and 320 min, while for RSCA, it occurs between 390 min and 550 min. It is noteworthy that under the same aperture, BSCA shows a faster hydration reaction, averaging 1.7 times that of RSCA. The crack initiation rate of single-hole specimens under RSCA is lower than that of BSCA, but the former has a higher crack propagation rate than the latter.  
The parameters of static fracturing agents play a crucial role in their effectiveness on fractured rock. Most literature analyzes these parameters using numerical simulations, with  
Figure 30: The variation rule of expansion pressure of double-hole specimen with different circumferential pressure.  
many scholars employing finite difference methods to simulate rock fracturing [23; 24; 26; 27]. However, these methods cannot visually display crack development patterns. This study utilizes the PFC2D particle flow inversion test process to validate parameter selection and demonstrate the feasibility of simulating static fracturing agents with PFC. It examines internal dynamic effects, crack propagation, and distribution characteristics, as well as the development laws of dual-porosity expansion pressure under different aperture sizes, spacing, and confining pressures. In conclusion, this study provides valuable insights into the fracturing mechanism of RSCA, contributing to improved efficiency in downhole rock fracturing. Nonetheless, it is important to note that the research findings have not yet been applied in real-world applications, and field testing would provide more effective validation of the results.