## 2 Experimental Setup and Procedures
### Linear Cutting Machine  
The linear cutting test is known as the most reliable method for the design and performance prediction of mechanical excavation machines [25]. Linear cutting machines can be classified into full-scale and small-scale linear cutting machines. Since the full-scale cutting machine uses a large sample, the test result can be directly used in an excavation machine [26]. Small-scale linear cutting machines were developed before full-scale machines [27]. Rock samples from small-scale linear cutting machines have the advantage of  
Figure 2: Cutting tool used in the experiment: (**a**) specification; (**b**) appearance.  
being easily and inexpensively obtained from core or rectangular block samples, obtained during a geological investigation [28].  
In this study, rock-cutting tests were performed using a small-scale linear cutting machine, as shown in Figure 4a. A linear cutting machine is divided into cutting and control systems. The cutting system includes a frame of the main body, bucket for holding rocks, driving device for a machine, and load cells. The control system consists of a computer and monitor.  
The linear cutting machine used in this study is driven by a servomotor rather than a commonly used hydraulic cylinder. The servomotor has the advantage of precision control in terms of the moving distance. The servomotor in the x-direction has a stroke of 500 mm in the left and right directions and is used to set the cutting spacing. The y-direction servomotor has a stroke of 700 mm in the front-rear direction and is used for cutting the rocks (Figure 4b). A z-direction servomotor is used to set the penetration depth. The servomotors in the x- and y-directions used a variable type, with a maximum speed of 100 mm/s.  
In general, the tool forces generated in three directions are measured using a triaxial load cell. However, in this study, three uniaxial load cells were installed in each direction to accurately measure tool forces. Because the side force (_Fs_) generated in the x-direction is relatively small, it was measured using a 15-ton load cell. The cutting force (_Fc_) and normal force (_Fn_) generated in the y- and z-directions, respectively, were measured using 25-ton load cells (Figure 4c). Because one cutting action is completed in a short time during a linear cutting test, a load cell capable of accumulating data at 50 Hz is used to increase the amount of available data and the reliability of the test results.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Target Strength** & **Elastic Modulus** & **Density** & **Poisson’s** & **Uniaxial Compressive** & **Brazilian Tensile** \\
**(MPa)** & **(Gpa)** & **(kg/m3)** & **Ratio** & **Strength, UCS** & **Strength, BTS** \\  & & & & **(Mpa)** & **(Mpa)** \\ \hline
20 & 16.92 & 2214 & 0.3 & 18.0 & 2.06 \\
30 & 33.35 & 2363 & 0.3 & 29.3 & 2.18 \\
40 & 38.92 & 2382 & 0.3 & 42.0 & 2.51 \\
50 & 44.47 & 2235 & 0.3 & 51.8 & 2.99 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Physical and mechanical properties of rock specimens.  
Figure 3: Tests to obtain the mechanical properties of rock specimens: (**a**) uniaxial compression and (**b**) Brazilian tests.  
The control system may set cutting conditions such as the penetration depth and spacing. As the cutting length, penetration depth, spacing, and number of cuttings were input, a series of cuttings were automatically performed. The tool forces generated during cutting were displayed in real time via the monitor. In addition, the speed of the servomotors and data measurement period of the load cell can be set.