Rock-Properties Estimation by TBM Cutting Force

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1. Introduction

At present, various types of tunneling boring machines (TBMs) are widely used as a substitute for conventional tunneling methods, i.e., drilling, blasting, and mucking. The performance of TBM is potentially far better than that of conventional methods. If TBM is properly applied, a mean penetration rate several times greater than those of conventional methods can be expected. However, TBM performance is very poor when applied under conditions that are adverse to TBM. Since TBM is a full-face machine, the face cannot actually be observed. This is disadvantageous when excavating rock which has rapidly changing characteristics, as is commonly the case for rock in Japan. Therefore, measuring geological characteristics forward of the face is essential. This measurement is generally performed using the wave reflection method. However, the relationship between wave velocity and the mechanical properties of rock is very complicated. Therefore, comprehensive estimation of the mechanical properties of rock is difficult using the wave reflection method.

In the present study, a method for estimating the rock strength of face using TBM cutting force, such as thrust, torque and cutting depth, is proposed. The response of rock to indentation by disc cutter has been the subject of several investigations. The thrust force of the disc cutter was found to be roughly proportional to the compressive strength of the rock. Moreover, the relationships between rock mass classification and TBM mechanical data, such as thrust, torque and penetration rate have been reported. The results obtained in previous studies indicate that the higher the rock mass classification, the lower the penetration rate and the higher the thrust. Thus, the TBM cutting force is correlated with the rock strength of face. For the TBM, maximum thrust and torque are determined by the compressive strength of rock. However, few studies have reported that rock strength can be estimated by the TBM cutting force.

The present study is an attempt to develop a method by which rock properties can be determined in real-time based on mechanical excavation data. In the present paper, a review of excavation tests performed using a disc cutter is presented, and the relationship between TBM cutting force and rock properties is obtained. In addition, rock strengths at the Niken-Goya tunnel and the Maiko tunnel are estimated from actual excavation data for sections that are a few hundred meters in length. These estimates are compared to those obtained using the bedrock survey and Schmidt-hammer rebound hardness. Finally, the estimated rock strength of the geological boundary at the Culter-Goodman tunnel is obtained.