## 2 Full-Scale Tests for Tunnel Boring Machine (TBM) Tunneling
### Development of Earth Pressure Balance (EPB) Shield TBM  
The KEPCO Research Institute and EMK companies manufactured the 3540 mm diameter EPB shield TBM machine comprising five hydraulic motors and seven hydraulic pumps which had the capacity to supply 630 kW power to the machine. Specifications of the developed TBM are provided in Table 1.  
Cutterhead was manufactured by hard facing welding and the gage cutters in cutterhead were designed for properly achieving a steep curved sectional excavation up to R30 m. A 3622 mm diameter of cutting was achieved by the 3560 mm diameter cutterhead which was designed so that the 3000 mm diameter of segmental linings could possibly be installed afterwards. The disc cutters provided in the cutterhead were divided into six center cutters, 12 face cutters, and eight gage cutters as shown in Figure 2a. The spacing among different kinds of disc cutters provided in the cutterhead was, accordingly, designed as shown in Figure 2b. The tunnel face was excavated in accordance with the cutterhead design, as shown in Figure 2c. An assembly of scrappers as well as 26 pieces of 17 in diameter disc cutters with average spacing of 68.5 mm between them was used to design the cutterhead. A constant spacing was provided among the individual center and face cutters. The spacing among the gage cutters was designed to be decreasing towards the periphery of the cutterhead ranging from the maximum spacing of 65 mm to a minimum spacing 20 mm spacing between gage cutters. The outer gage disc cutters were designed at a 25-degree angle from the vertical axis because the gage cutters are responsible for overcutting in order to achieve a smooth excavation and also to prevent jamming in the periphery of the cutterhead. The scrappers were provided in the cutterhead for achieving a flat tunnel face during excavation. They also facilitate in the collection of chips and debris into the chamber. \begin{table}
\begin{tabular}{c c} \hline \hline
**Design Parameters** & **Specifications** \\ \hline Disc cutter & 26 pieces each of 17 in. size \\  & (6 center, 12 face, 8 gage) \\  & 68.5 mm average spacing \\ Shield body & 3540 mm (Shield diameter), 7240 mm (Length) \\  & 3622 mm (Cutting diameter), 3560 mm (Cutterhead diameter) \\  & Maximum 1309 kN-m torque \\ Cutterhead & Maximum 10.5 RPM (Revolutions per minute) rotation speed \\  & 19.3\% open ratio \\  & Up to 5 bar of seal protection \\  & Maximum 12,000 kN thrust force \\ Shield jack & 1750 mm stroke \\  & Maximum 10,000 kN thrust force \\ Articulation jack & X Type \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications of the developed EPB shield TBM. Figure 2: Cutterhead design and tunnel face, (**a**) Schematic view of cutterhead design; (**b**) sectional view depicting cutterhead spacing design; (**c**) Excavation front. As mentioned previously, the cutterhead driving was achieved by a set of five hydraulic motors and seven hydraulic pumps which had the capacity of supplying 630 kW power to the machine. The assembly of hydraulic pumps, oil units and various components related to the machine is illustrated in Figure 3. The cutterhead could reach a maximum rotational speed of 10.5 RPM for a developed torque of up to 450 kN\(\cdot\)m, and it could rotate up to 3 RPM at a maximum torque of 1309 kN\(\cdot\)m. As shown in Figure 4, the cutterhead drive capacity can be expressed by the relationships between torque and rotational speed of the cutterhead, therefore, a single hydraulic pump was designed to rotate the cutterhead at maximum 1.5 RPM which could develop 25.82 kN\(\cdot\)m of torque. So, by utilizing seven hydraulic pumps, the rotational speed of 10.5 RPM can develop 1309 kN\(\cdot\)m torque by using 320 bar of oil pressure from the pumps. Figure 4 shows an example of the experimental results at different operational parameters within the cuttherhead drive capacity. The cutterhead drive capacity is a good tool for presenting the operational conditions of the TBM based on the relationships between torque and cutterhead rotational speed.