# Analysis of Blasting Efficiency Using Crack-Inducing Holes and Pre-Splitting Method in Blasting
## 1 Introduction  
Underground excavations in urban areas are primarily carried out for the construction of road and railway tunnels to expand transportation networks. Methods for excavating rock-based tunnels can be broadly categorized into blasting methods, which use high-power explosives, and mechanical excavation methods, which crush rock using machinery. With the increasing trend of tunnel excavation projects, various excavation methods have been developed and commercialized. However, from the perspectives of constructability and cost-effectiveness, blasting methods maintain a comparative advantage. Nonetheless, blasting excavation has drawbacks, including complaints arising from vibrations caused by the use of high-power explosives and the tendency for overbreak to expand in weak or highly jointed rock formations [1, 2, 3]. An analysis of the environmental dispute statistics published by the Ministry of Environment in December 2023 shows that complaints related to construction site noise and vibration have been increasing annually from 2019 to 2023, posing significant constraints on blasting operations [4]. As a result, extensive research has been conducted to minimize blasting-induced vibrations and overbreak.  
One way to reduce blasting vibrations is by improving the tunnel cut area. [PERSON] et al. (2012) showed that installing large-diameter blast holes in the tunnel cut area zone resultedin reduced blasting vibrations compared to conventional V-cut blasting methods [5,6]. However, a downside is the need for special drilling equipment to be deployed inside the tunnel, additional safety measures, and extra time for work. To minimize overbreak, [PERSON] et al. (2013) proposed overbreak management using artificial neural networks and the Overbreak Resistance Factor [7, 8, 9, 10], but they did not suggest drilling or blasting patterns for different rock types. [PERSON] et al. (2018) conducted a sensitivity analysis using artificial neural networks and concluded that drilling, blasting, and RMR were the most effective factors for overbreak control [11], but they did not propose a blasting method. [PERSON] et al. (2023) optimized tunneling parameters and overbreak prediction modeling for various tunnel cross-sections [12,13] but faced limitations due to numerical analysis. To reduce blasting vibrations and minimize overbreak, [PERSON] et al. (2007) developed a notch bit for forming notch grooves on the outer sections [14,15], but, due to wear, jamming, and other issues during drilling, there are few cases of its application in practical fieldwork.  
The efficiency of blasting during tunnel excavation can vary depending on rock characteristics and drilling conditions, and the areas where vibrations are most intense can also differ. Considering the rock characteristics, which are an unchanging parameter in blasting operations, adjusting the drilling patterns and detonation sequences would be the most effective approach. However, there is a lack of research on methods to minimize vibrations and overbreak during tunnel blasting without the need for additional equipment. Therefore, it is essential to develop technologies that can block and reduce vibration generation.  
Full-scale comparative blasting experiments were planned and conducted by the authors at a railway tunnel construction site using a blasting method that combines crack induction holes and presplitting blasting techniques to minimize overbreak and control vibrations alongside the conventional Smooth Blasting method in this study. The ground vibration propagation characteristics and overbreak amounts from the combined blasting method and from the typical Smooth Blasting method were compared and analyzed.