# Theoretical Study of Large Uncoupling Coefficient Loading for Surface Blasting
## 1 Introduction
The understanding of the relationship between cracked-zone radii and the dominant frequency of vibrations during tunnel blasting was studied by [PERSON] et al. [20] using theoretical, numerical, and in situ measurement approaches. The rock fragmentation induced by blasting using a decoupled charge is investigated by [PERSON] et al. [21] combining finite element modelling and image processing. The results showed that rock fragmentation became finer, and the fragmentation size distribution range becomes narrower with the decrease in the decoupling ratio. [PERSON] et al. [22] found that for the Liuzhi-Anlong highway tunnel blasting construction, light surface blasting effects are poor, and by using a numerical simulation to optimize the reasonable blasting parameters, they found that the radial uncoupling coefficient of 1.25 and the distance between the holes for the site of the 55 cm blasting application produced good results. [PERSON] et al. [23], through the test to explore the effect of uncoupled charges on the concrete blasting effect, produced results that show that the optimal uncoupling coefficient is 1.85 when the air is not in a coupled charge; polystyrene (EPS) foam is not coupled to the optimal uncoupling coefficient of 1.65 when the charge is not coupled. To facilitate the loading, the diameter of the explosive charge is generally kept smaller than the diameter of the blast hole. To avoid excessive crushing of the hole wall, the axial and radial uncoupled charging are used widely in the smooth surface blasting construction process. Smooth blasting operations in roadways and tunnels are limited by the size of the excavation section and the direction of excavation. To maintain the effectiveness of light blasting, air-legged rock drills are still used more often in the open terrace or slope light blasting with a drill hole diameter of 42 mm and charge diameter of 25 mm or 12.5 mm [15]. However, with the advancement of drilling machinery such as crawler hydraulic submersible drills, a larger diameter (90-140 mm) is often adopted for smooth blasting holes in open slopes to accelerate the construction progress and mechanization level, while still using an explosive charge diameter of 32 mm or 35 mm [15; 24]. [PERSON] et al. [25] used large-diameter deep-hole blasting for ore chipping in mining, according to the actual ability of the engineering site to use the uncoupling coefficient of 2.36 of the charging structure and achieve good application results. Using a charge with a larger uncoupling factor can increase the quasi-static effect of explosive gas, while reducing the damage incurred to the blast hole. The classical theory of smooth blasting considering large uncoupling charging has not been well analyzed and solved for the blast parameters of large uncoupling charging [26; 27; 28; 29; 30; 31; 32; 33]. The present study aims to determine the axial and radial uncoupled charge coefficients, the force acting on the blast hole wall, and the distance between adjacent blast holes under the action of an uncoupled charge in order to effectively improve the utilization rate of explosive energy and improve the blasting effect. From the blasting theory, axial and radial critical uncoupling coefficients are solved according to the actual detonation expansion law. The calculation methods for estimating quasi-static pressure, uncoupling coefficient, and blast hole spacing under the action of a large uncoupling coefficient charge were explored based on the requirements of the structure of smooth surface blasting and field charging. A slope in Guizhou was taken as the research subject for the present study. The proposed light surface blasting method was applied in the field, and satisfactory light surface blasting effects were obtained.