Rock-Properties Estimation by TBM Cutting Force


6. Conclusion

In the present study, a method is proposed for estimating face-rock strength from TBM cutting force. Rock strength along the Niken-Goya and Maiko tunnels is estimated from actual excavation data for sections a few hundred meters in length. The estimated strengths were then compared with those obtained using the bedrock survey and Schmidt-hammer rebound hardness. Estimated rock strengths were found to agree well with those found using these surveys. In addition, rock strength was estimated using the geological boundary at the Culter-goodman tunnel. The estimation was found to be in good agreement with the uniaxial compressive strength of rock. Therefore, the proposed method provides a useful method for properly selecting a supporting pattern for rapidly changing rock mass characteristics, thereby preventing accidents and reducing construction time and expense.

Equations (5) and (6) for estimation using thrust and torque, respectively, are based on previous laboratory excavation results, and may be applied independently. It is very important for high reliability of estimated rock strength. The tunnel environment, i.e., moisture and temperature conditions, provides a severe measurement environment; however, rock strength estimated from the thrust can be compared to that estimated from the torque to provide a highly reliable estimation method.