Rock-Properties Estimation by TBM Cutting Force

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4. Maiko Tunnel

The Maiko tunnel is a roadway tunnel of 3.3 km in length located in western Japan. A TBM having a diameter of 5 m was used to excavate a 600 m section of the tunnel. The rock in this tunnel consists of Rokko-granite. Cutting depth, thrust, torque and rock strength estimated using the Schmidt-hammer rebound hardness are shown in Fig. 3 (Kono, 1995). Rock mass strength is calculated using Equation (7). Torque remained almost constant (500 kNm). At 260 m, cutting depth is maximum (6 mm) and rock mass strength is minimum (50 MPa). At 500 m, cutting depth is minimum (2 mm) and rock mass strength is maximum (250 MPa). Cutting depth was found to correlate with rock strength, and therefore verifies Equation (6).

In Fig. 4, rock strength estimated using thrust is indicated by a solid line, and that estimated using the Schmidt-hammer rebound hardness is indicated by solid circles. Constant c1 is defined in a manner similar to that used for the Niken-Goya tunnel. At 0-50 m, 250-280 m and 510-580 m, rock strength estimated using thrust and that estimated using the Schmidt-hammer rebound hardness are below 100 MPa. Both estimates showed a maximum at 500 m, revealing that these methods agree well.

In Fig. 5, rock strength estimated using torque and that estimated using the Schmidt-hammer rebound hardness are indicated by a solid line and circles, respectively. Rock mass strength estimated using thrust is found to agree well with that estimated using the Schmidt-hammer rebound hardness.