## 5 Theoretical Case Study, Results, and Discussion  
### Project Overview  
TBM predictions help control the construction risk related to cost, operation, and decision under certain conditions. Machine and rock parameters should be incorporated into the model to predict the performance of TBMs close to reality. This research collected data from the NJHEP project, the second largest hydropower tunneling project globally (Figure 12). Two TBMs were used to excavate twin tunnels, each 10 km in length. TBMs were adopted to enhance the project's productivity, but due to the complex nature of geology, the TBMs faced serious problems [61]. The TBM tunnels are driven in the central portion of a zone bounded by two major Himalayan faults. The first is the Main Boundary Thrust Fault, and the second is the subsidiary reverse or Muzaffarabad Fault. The first fault extends through the mountain range's length following the Neelum River's course at the upstream start of the headrace tunnels at Nauseri, while the second fault runs close to the course of the Jhelum River at Thotha. A rupture along this fault in 2005 resulted in the Muzaffarabad earthquake, which caused over 75,000 fatalities.  
The project is located at the foothills of the northwestern Himalayas (Murree Formation), where the infrastructure is inadequately developed. The Murree Formation comprises tight folding with repeated faulting and fracturing, indicating a high structural compression. Three detailed laboratory testing programs were conducted at the feasibility/detailed design, commencement of construction, and construction phase to determine rock parameters. Three main rock units of the Murree Formation, sandstone, siltstone, and mudstone, were found and classified during the detailed design stage. Sandstone is well cemented, generally strong, fine- to medium-grained, greenish-grey to grey, and moderately to closely jointed. Silstone is strong to medium-strong, greyish brown to brown and reddish-brown, and closely jointed. Mudstone is weak to medium-strong, fine- to very fine-grained, reddish-brown, and closely jointed. Table 2 summarizes some of the intact rock mass parameters of the Murree Formation.  
Figure 12: Neelum Jhelum project: (**a**) layout showing the alignment of TBM twin tunnels and other marked features; (**b**) terrain profile of the tunnel.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Parameter** & **Sandstone** & **Silstone** & **Mudstone** \\ \hline Color & Gray & Brown– reddish-brown & Reddish-brown \\ Weathering & Fresh–slightly & Fresh–Slightly & Fresh–slightly \\ Structure & Massive, blocky, locally irregular & Blocky, Tabular, Locally Irregular & Tabular, blocky, irregular \\ Grain size & Fine–medium & Very fine–Medium & Very fine \\ Bedding & Thick–massive & Thin & Very thin–ythin \\ Bulk density, kg/m\({}^{3}\) & 2730 & 2771 & 2722 \\ Uniaxial compressive strength, MPa & 86.0 & 56.5 & 33.0 \\ Average rock quality classification & Good & Fair & Poor \\ Volumetric joint count (joints/m\({}^{3}\)) & 1–22 & 3–25 & 3–25 \\ Number of joints sets & 2 + random to 3 + random & 3 to 3 + random & 3 to 3 + random \\ Joint roughness, waviness & Rough, planar–undulating & Rough–smooth, planar & Smooth, planar \\ Joint aperture or thickness (mm) & \textless{}0.1–10 & 0.1–10 & 0.25–5 \\ Joint filling & Clean, sandy particles, or hard calcite & Clean, sandy, or silty coatings & Silty or clayy coatings, occasionally \\  & & & soft clay \\ \hline \hline \end{tabular}
\end{table}
Table 2: Intact rock parameters of the main rock types.