# The Efficiency of Large Hole Boring (MSP) Method in the Reduction of Blast-Induced Vibration
## 2 Project Description  
### Introduction to MSP Method  
The main purpose of the MSP method is to reduce the blast-induced vibration as one of the cut methods by boring a large empty hole, as shown in Figure 1. A cut blasting method using a large hole involves the utilization of 250-1000-mm diameter empty holes in Korea [14]. The MSP method usually includes 50 m boring length using a high-performance boring machine with a 382 mm hammer bit: 20 to 60 m depths can be drilled depending on the conditions of a site. This method can be used to simplify the blasting patterns of the cut area compared with other methods.  
Figure 1: Comparison of the principle between (**a**) general blasting method and (**b**) multi-setting smart-investigation of the ground and pre-large hole boring (MSP) method.  
This large empty hole plays an important role in the reduction of the initial vibration by releasing the confining stress of the tunnel face before blasting, and the residual energy after rock breaking. In addition, the compressive stress wave generated by the explosion is reflected as a tension stress wave when it reaches the free face, and tensile strength of rocks is typically much lower than compressive strength; therefore, the explosives loaded into a charge hole at the cut area can break rock more efficiently [18; 19; 20; 21; 22; 23]. The boost of tensile failure by producing a large-diameter empty hole at the excavation surface, which is longer than the length of the blast holes, greatly contributes to the efficiency of the blast force, thus it has a great advantage in increasing the excavation length [15].  
Figure 2 depicts an earlier version of a boring machine and the newly developed high-performance MSP boring machine. One of the main issues with the old machine was a lack of mobility and necessity for multiple construction vehicles (crane, truck, etc.) for transportation and setting of the boring machine. Furthermore, a transition between various functionalities was incorporated, and required accessories and other parts to be carried around separately and manually installed. In contrast, the high-performance MSP boring machine is capable of independent movement and setting utilizing a remote control and crane system, which significantly reduces installation and uninstallation times by more than 50% compared to older boring machines. A hydraulic power pack system that generates electric power is used for boring without a diesel engine. This system improves the working environment by reducing the smoke in the tunnel.  
Figure 3a shows the applications of the MSP method at tunnel and shaft construction sites. This method is also used to create a free face to increase the breaking efficiency when applying a hydraulic rock splitter, which is a non-vibration excavation method, as shown in Figure 3b. The machine can not only be used for boring in the vertical shaft through mode conversion, as shown in Figure 3c, but also for slope boring in the range of 0-90\({}^{\circ}\).  
Figure 3: Field applications of MSP method: (**a**) horizontal tunnel for blasting, (**b**) horizontal tunnel for non-vibration excavation, and (**c**) vertical shaft for blasting.  
Figure 2: Comparison of boring machine: (**a**) outdated boring machine, and (**b**) newly developed high-performance MSP boring machine.