## 5 Engineering Cases and Comparative Analyses  
### Hard-Rock Cutting Cases and Analyses  
Rock strength and abrasiveness determine the performance and life of a cutter, allowing us to study the engineering cases of different strength rocks, establish the wear theory under the action of thermal effect, and calculate the predicted life and wear amount of the cutter under the joint action of heat-force [39]. Three project cases of cutting hard rock are selected for a comparative study. The comparative study is carried out to verify the accuracy of the prediction model [9]. This provides a basis for the application of prediction theory, which is important for safe construction and economic efficiency. The case of disc cutter cutting of hard rock requires the selection of shield construction projects with different rock strengths. The effect of different rock types, such as high-extremely high hard rock, medium-very high hard rock, and medium hard rock, on the cutter ring wear is analysed. It is necessary to select the same range of installation radius, shield machine cutter head diameter, individual cutter thrust, cutter speed, etc., which is conducive to cutter ring wear data statistics. Rock samples of different strength types have different characteristics, and their physical properties and mechanical parameters play an important role in the cutting process. Three rock types were selected: high-strength hard rocks, such as slightly weathered granite and basalt, with a uniaxial compressive strength higher than 120 MPa and thermal conductivity lower than 3.1 W/m\(\cdot\)\(\cdot\)\(\cdot\)C; medium-hard rocks, such as marble, dolomite and moderately weathered granite, with strengths in the range of 40-120 MPa and a thermal conductivity of 3.1-3.6 W/m\(\cdot\)\(\cdot\)\(\cdot\)C; and a selection of soft rocks, such as sandstone, gneiss, mudstone, etc., with a strength of less than 40 MPa and a thermal conductivity of more than 3.6 W/m\(\cdot\)\(\cdot\)C.  
[PERSON] [2] of the Norwegian University of Science and Technology (NTNU) selected a project in north-central Europe and collected data on shield cutter ring damage. Hard rock is predominantly distributed in the excavation area of this tunnel. It is dominated by hard granites, mostly above 120 MPa, with an average UCS of 198 MPa and tensile strength (BTS) of 2.1-3.3 MPa. The excavation of granite, quartz and diorite accounted for about 75% of all rocks. The various types of rocks show an uneven distribution, which tends to exacerbate the effects of abrasion. [PERSON] et al. of Shanghai Jiao Tong University (SJTU) [15] selected the Mumbai Metro Tunnel Line 3 project for their study. The rock formations of the tunnel section present a complex lithological assemblage, with hard rocks of high strength predominantly distributed in the excavated area. The rocks are mainly composed of fine-grained green basalt, moderately weathered basalt, slightly weathered basalt and breccia. It exhibits large heterogeneity, with strengths distributed in the range of 80-120 MPa, and the depth of the rock layer is 16.5-18.0 m.  
[PERSON] (TUM) has statistics on case studies of tunnelling in central Europe [12], a region with predominantly earth-rock composite formations with hard rocks of medium strength, such as marble and limestone. Abrasion resistance tests were carried out on different types of rocks to summarise the CAIs of different rocks. [PERSON] (BJU) selected the case data of Shenzhen Metro Line 6 [1], where marble and moderately weathered granite are distributed in the excavation area, with a strength distribution in the range of 40-80 MPa. The average compressive strength is 70.6 MPa, and the average tensile strength is 6.5 MPa. Uniform wear is the main cause of tool failure, accounting for about 91.71%, and non-uniform wear only accounts for 8.29%, and both cases are hard rock of medium strength.