## 2 Non-Vibrational Rock Splitting Method  
The most important feature of non-vibrational rock splitting method is the split-wedge system that consists of a combination of a steel wedge and two counter-wedges, widely used in the construction industry for rock splitting by inserting it in the already drilled boreholes in the rock [8], as illustrated in Figure 2. This system can be easily mounted on an excavator in less than 10 min and requires only one person to operate. This saves the manpower required by the other types of excavation methods from being used. Usually, the excavators are commonly available with the contractors so relatively cheaper investment has to be made for using the split-wedge system. Much less time is required to learn about the efficient operation of this system. The use of this rock splitting method is very safe as there is always a safe distance between the rock face to be excavated and the excavator in which the driver sits. Continuous excavation process can be carried out using this mechanized method in the form of borehole drilling, rock splitting, and hauling procedures conducted simultaneously. This makes it very easy to break and excavate the rock material without causing the vibration, noise and dust problems as compared to other mechanized as well as blasting methods. The boreholes are drilled in a formation, at first, in the rock using jumbo drill so that  
Figure 1: Classification of intact rock based on modulus ratio concept. Figure 2: Illustration of rock splitting process. the rock splitting process could be initiated. The general features of split-wedge system and borehole configuration widely used in the construction industry (for instance [9]) are given in Table 1. Due to the splitting action by the split-wedge system, around 70% of the borehole depth usually fragments out and some part of the borehole remains there even after the initial excavation cycle. The spacing between the individual boreholes depends on the strength properties of the rock. The harder the rock material is, the smaller the borehole spacing it will require for the rock splitting process. The non-vibrational rock splitting method also requires a free surface to be artificially formed at the working face, just like the other mechanized and blasting methods used for excavation. Free face is any natural or excavated space towards which the rock mass can move during the splitting action due to fracture propagation. In order to create free surface for the excavation process, various methods have been proposed [10; 11], but these methods have some limitations such as the requirement of a special forming device, accuracy and efficiency of the forming in continuity. Considering these limitations, the jumbo drill is generally used not only to create the free surface but also the borehole drilled for rock splitting process. The boreholes must be sufficiently deep and in a straight alignment for conducting successful rock splitting process. Vertical boreholes are recommended to be covered with a cloth after drilling so that the rock fragments do not enter the borehole and borehole depth is effectively maintained. The illustration of one of the conceptual borehole configuration and free surface is shown in Figure 3.  
After the completion of borehole drilling, the split-wedge system is mounted on the excavator and is then inserted in the borehole adjacent to the free surface. The main cylinder of the excavator exerts \begin{table}
\begin{tabular}{c c} \hline \hline
**Characteristic Feature** & **Magnitude (Units)** \\ \hline Power of maximum rock splitting (kg) & \(2.18\times 10^{6}\) kg \\ Length of counter-wedge (mm) & 1000 mm \\ Borehole splitting width (mm) & 15–20 mm \\ Depth of drilled borehole (mm) & 1000–1400 mm \\ Borehole diameter (mm) & 76 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristic features of split-wedge system and borehole. Figure 3: Conceptual borehole configuration and free surface.