## 2 Materials and Methods
### Project Descriptions  
This section provides a brief overview of the six projects shown in Figure 1, whose data are used in this work. The first four projects are completed, and are presented in the manuscript as Project 1, 2, 3, and 4, which are based on the number of sections used in this work. The last two, Project 5 and 6, are the planned one, and their geotechnical data is used in the numerical modeling for validation. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Ground Behavior**} & \multicolumn{2}{c}{**Empirical Rock Mass Classification System**} \\ \cline{2-4}  & **RMR** & \(Q\) & \(RMi\) \\ \hline Raveling from slaking or friability & 4 & 4 & 4 \\ Swelling ground & 4 & 3 & 3 \\ Flowing ground & 4 & 4 & 4 \\ Water ingress & 4 & 4 & 4 \\ \hline \hline \end{tabular}  
* Fitness rating of different systems: 1, suitable; 2, fair; 3, poor; and 4, not applicable [15].  
\end{table} 
Table 1: _Cont._  
Figure 1: Location of the projects. **Project 1**  
The Lowari Rail Tunnel (LRT) is 8.5 km, and is the longest transportation tunnel in Pakistan, connecting the north district, Chitral, with the remainder of the country for vehicle transportation on an all-weather link road. The cross-sectional design of the tunnel was modified by the National Highway Authority (NHA) of Pakistan after the excavation of the LRT (7.12 m in span), for a road tunnel and named the Modified Road Tunnel (MRT). This MRT (11.17 m in span) is a part of the extension of road network for connecting Central Asian countries with Pakistan through the Chitral district, traversing Vakhan (Afghanistan). The geological formation of the project area is located between the active Eurasian continental plate and the Indian plate, and due to the ongoing subduction of the Indian plate, this area belongs to the active seismic zone. Based on the geological investigations for the LRT, five major geological units were defined along the tunnel route: the granite unit, the meta sediment unit, the meta volcanic unit, the meta igneous unit, and the biotite granite unit [31]. The LRT and MRT were completed in 2009 and 2016, respectively, and became operational for traffic in 2017. **Project 2**  
The Neelum-Jhelum Hydroelectric Project (NJHEP) of the Water and Power Development Authority (WAPDA) of Pakistan is located in Muzaffarabad, within the Kashmir region in northeast Pakistan. A number of underground structures are part of this 969 MW run-of-the-river project, including a diversion tunnel, headrace tunnels, a tailrace tunnel, access tunnels, a powerhouse cavern, and pressure shafts. The 28.5-km headrace tunnels convey the water of the Neelum River and pass beneath the Jhelum River. These headrace tunnels are a combination of single and twin tunnels. The twin tunnels (each with a span of 9.68 m) were excavated by the conventional method and a tunnel-boring machine (TBM). These tunnels pass through the Murree Formation of alternating beds of sandstone (medium to fine-grained) and siltstone with layers of occasionally thin mudstone [30; 32; 33]. The sandstone (SS) is further divided into two subcategories, SS-1 and SS-2, based on their mechanical properties. SS-1 is made up of comparatively strong, well-cemented sandstone, of fine to medium grain. It is also thinly to thickly bedded, massive at places, blocky, moderately to closely jointed, and at places fractured [34]. **Project 3**  
The Kohat Tunnel (KT)--also known the Pak-Japan Friendship Tunnel or simply the Friendship Tunnel--is an alternate route for traversing Kohat Pass in the Khyber Pakhtunkhwa province of Pakistan along the major national highway of NHA (known as the Indus highway), and follows the west bank of the Indus River. The 1.9-km, two-lane road tunnel was the first long road tunnel (9.4-m wide) in the country, and was open to traffic in 2003. Difficult geological sites were encountered during excavation. Along the tunnel route, the major rock types were limestone and shale [35].