## 3 Methods
### Truck Haulage Simulation  
In this study, a discrete event simulation that can simulate the truck haulage system in the study area is developed. The simulation's algorithm is based on the truck cycle time theory proposed by [PERSON] [53]. In the truck cycle time theory, individual trucks' operation times are expressed as in Equation (1):  
\[\text{TCT}=\text{STL}+\text{LT}+\text{TL}+\text{STD}+\text{DT}+\text{TE}+ \text{AD} \tag{1}\]  
where TCT is the truck cycle time; STL is the time during which a truck is accessed by the loading equipment; LT is the time during which the ore is loaded; TL is the time during which the loaded truck travels to the crushing site; STD is the time during which the truck is accessed by the crusher (outdoor storage site); DT is the time during which the ore is dropped off; TE is the time during which the truck travels to the loading site after performing the ore drop-off operation; AD is the time during which the truck waits during ore loading and drop-off. Figure 5 shows the algorithm of the truck haulage system simulation. When the simulation begins, a truck's destination is assigned by a real-time dispatching method. The truck departs from the crushing site and travels to the W01 AP located at the mine entrance (TE1). Then, it travels to the W01-W02 segment (TE2) and W02-W03 segment (TE3). The truck travels toward the assigned destination from the crossroads located close to W03. It performs the ore loading operation and returns to W03 (K). Then, it travels to the W03-W02 segment (TL1) and W02-W01 segment (TL2), and it travels from the mine entrance to the WC located at the crushing site (TL3). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Heading** & **Data Name** & **Data Type** \\ \hline \multirow{3}{*}{Inputs} & Two type of truck tag ID (UWB \& 900 MHz frequency) & Constants \\  & Original packet data obtained in the underground mine & ASCII \\  & Original packet data obtained in the crushing zone & ASCII \\ \hline \multirow{2}{*}{Outputs} & Tag recognition time & ASCII \\  & Truck travel time & ASCII \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Description of the input data and output data of the program developed for measuring truck travel data. Figure 5: Flow chart showing procedures for implementing the truck haulage simulation algorithm. The truck that arrives at the crushing site checks whether there are trucks waiting to perform the ore drop-off operation. If there are trucks waiting, the truck waits until the waiting trucks complete the ore drop-off operation (AD). If there are no trucks waiting, the truck drops the ore off in the hopper (DT). This operation also includes cases where the truck travels to the outdoor storage site and drops the ore off if the amount of ore in the crusher hopper exceeds the limit capacity. The user-specified simulation end time and the simulation's absolute time are compared to determine whether the truck will perform the loading operation again or whether the simulation will end. The Windows-based truck haulage simulation program employed in this study consists of a graphical user interface (GUI) and a simulation engine. Through the GUI, a user can enter the simulation factors (operation days, daily operation time, number of trucks, truck weight, etc.) and temporal factors (truck operation time, ore drop-off time, etc.) that are required to run the simulation. Table 3 lists the input and output data of the program. The averages and standard deviations of the temporal factors are calculated through statistical analysis using the truck travel times for all haulage cycles obtained in Section 3.1. The simulation engine runs when the user finishes inputting the simulation factors and clicks the 'Run' button. The simulation results can be seen by clicking the 'View' button. The simulation engine was developed based on GPSS/H, which is a typical simulation language. Please refer to [PERSON] [54; 55] for a detailed description of the GPSS/H language. The simulation engine performs three functions.