## 5 Engineering Cases and Comparative Analyses
### Soft-Rock Cutting Cases and Analyses  
The loose ground and soft-rock particles are plastically deformed by the squeezing action of the cutter ring, and radioactive cracks are less likely to occur. The side of the cutter is always in contact with the soft-rock excavation surface for a long time and produces continuous friction. The lateral force exists in the whole cutting process. For the case study of cutter cutting soft and hard rocks, different rock strength types need to be selected. The main types of rocks are soft and hard composite strata of low to medium strength, such as mudstone and medium-weathered granite. In addition, the same type of cutter, similar rock density and the same range of cutter installation radius are required. Numerous observations have shown that continuous lateral wear reduces the frontal rock-breaking capacity of the cutter. Cutting soft and hard composite strata is prone to uneven wear of cutter body [36]. The contact friction of cutting soft rock will cause the cutter  
Figure 21: Distribution of wear depth with shield distance. Fitted value and comparative study of Yu.H 2021 [15]. (**a**) Radial wear at R = 1650 mm. (**b**) Radial wear at R = 2475 mm. (**c**) Radial wear at R = 3300 mm. ring material to flake off, resulting in sharpening of the curved excess area on both sides of the cutter head. It is necessary to assess the condition of the cutter with the wear quality when cutting soft rock. The boring parameters and soft-rock geological characteristics of the soft-rock cutting project case are shown in Table 3.  
[PERSON], [PERSON] et al. conducted an experimental study on shield cutter wear using rock samples from the Shenzhen City Railway Tunnel Project [41]. The tunnel area mainly includes highly weathered granite and moderately weathered granite. The unconfined average compressive strengths were 11.5 MPa and 36.2 MPa, respectively, and the average value of tensile strength was 1.23 MPa, as shown in Figure 22a,b. Scholars [PERSON], [PERSON] et al. selected the engineering case of the Yintao project #9 tunnel for their wear prediction study [42]. The cutter ring wear and cutter replacement distance were determined according to the actual construction situation. The geological stratum of the project includes sandy mudstone, granite, diorite, conglomerate and other composite rock bodies with an average compressive strength of 36.5 MPa. Comparative analyses of soft-rock cutting cases found that the theoretical predictions of the radius wear depth and mass wear were generally lower than the actual measured values. The wear prediction model that takes into account the thermal stress effect is closer to the actual measured values. The predicted wear when cutting soft rock increases with  
Figure 22: Distribution of wear level for cutting soft rock. (**a**) Distribution of wear depth with installation radius, [PERSON]. Z 2020 [41]; (**b**) distribution of wear mass with cutting distance, [PERSON]. L 2021 [42]. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{3}{c}{**Project Cases**} \\ \cline{2-3}  & **Shenzhen Case** & **Gansu Case** \\ \hline Project location & East Asia & East Asia \\ Approximate tunnel length (km) & 2.7 & 18.2 \\ Rock samples & Highly/moderately weathered granite & Mudstone and gneiss \\ Rock strength range & Low–medium & Low–medium \\ UCS (MPa) & 5–18/15.7–56.8 & 5–68 \\ Rock density (g/m\({}^{3}\)) & 2.3 & 2.6 \\ Tunnel diameter (m) & 8.5 & 5.75 \\ Disc cutter diameter (mm) & 432 & 432 \\ Cutter head rotation speed (rpm) & 1.8–2.0 & 0–8.1 \\ Cutter thrust (kN) & 500–600 & 21,420 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: TBM boring parameters and soft-rock geological characteristics of shield engineering [17; 41; 42]. the radius, and the growth rate decreases. The error is about 13.6%, and the wear prediction error considering thermal effects is 9.3%.