## 1 Introduction  
Two common rock tunneling techniques are (1) mechanical method, and (2) drill and blast/conventional excavation methods. The primary differences between them are the excavation sequences, support installation, and construction progress. The conventional method has a wider range of applications in both new tunnels and enlarged existing tunnels [1]. The mechanical method includes a tunnel boring machine (TBM), roadheader, and pre-cutting machine. Selection of the excavation method depends on ground composition and project-related features, and the selected method directly affects the project schedule and cost [2]. TBMs and roadheaders are widely used in new tunnel construction; however, the pre-cutting machine has comparatively high applicability in the enlargement of existing tunnels. A pre-cutting machine is a tunnel excavation machine that excavates using a cutting tool, such as TBMs and roadheaders. In the operation of a tunnel excavation machine and design of the cutterhead, the physical and mechanical properties of the rock and excavation conditions, such as penetration depth and spacing, must be considered. The pre-cutting method is a mechanical tunneling technique performed using a pre-cutting machine. In this method, a free surface is formed by pre-cutting along the edge of the planned tunnel cross section using an oversized chain-saw-shaped cutter head (Figure 1). Because the effects of excavation and blasting cannot pass through a free surface [3; 4], this technique does not disturb the surrounding ground, prevents ground settlement, and can accelerate tunneling [5]. This tunneling technique is economical, with a uniaxial compressive strength of approximately 70 MPa, and can be applied up to 100 MPa over short distances [6]. This tunneling technique was first introduced in the United States of America in 1950 and later rediscovered in France in 1970 and applied to the construction of transportation tunnels [6]. Incomplete statistics show that approximately 30 tunnels were built using this technique in France and Italy during the 1980s and 1990s [7]. In recent years, tunnel widening using pre-cutting machines has proven to be a good means of expanding the capacity of existing roads, highways, or railway tunnels while maintaining traffic flow [8; 9] (Figure 1b). Therefore, the demand for mechanical precutting is expected to increase. Numerous studies have been conducted to provide useful information for the design and operation of TBMs and roadheaders. [PERSON] et al. [10] analyzed the effects of excavation characteristics by penetration depth and spacing in cutting selected British rocks using TBM disc cutters. [PERSON] [11] investigated the excavation characteristics of a disk cutter for cutting anisotropic rock and provided useful performance predictions. [PERSON] et al. [12] analyzed the excavation characteristics to predict the performance of a TBM from the cutting test of Colorado red granite. [PERSON] et al. [13] investigated the relationship between optimal specific energy and rock properties in a roadheader using linear cutting tests. [PERSON] et al. [14] investigated the dominant rock properties that affect the performance of conical picks using rock-cutting tests. [PERSON] and [PERSON] [15] analyzed the effect of rock properties on the specific energy during cutting using pick cutters. [PERSON] et al. [16] analyzed the effect of penetration depth and spacing on the cutting performance when cutting using conical picks. [PERSON] and [PERSON] [17] provided useful information after analyzing the mechanical excavation characteristics based on cutting conditions during cutting using a chisel pick. [PERSON] et al. [18] investigated the relationship between the specific energy and physical and mechanical properties of rocks excavated by roadheaders. [PERSON] et al. [19] analyzed the excavation characteristics of granite under conical picks using indentation tests. However, the excavation characteristics of the pre-cutting machines were not analyzed compared to TBMs and roadheaders.