Abstract
Information concerning the size and shape of tunnel boring machine (TBM) debris is essential for designing efficient loading, hauling and dumping systems for TBM excavation. It is also very important in deciding how to recycle the TBM debris. However, only very limited information is available at present, and theoretical or calculation methods to estimate the size and shape are still open to discussion. In this paper, the size and shape of TBM debris are estimated by the well-known Nishimatsu's equation that is usually applied to roadheaders or shield-type machines with chisel bits. In this study, the equation was applied to the case of TBM excavation with disc cutters in which the shear failure or plane extends from a new groove to an adjacent pre-existing one. The estimated size and shape of TBM debris were found to be consistent with the measured results. Side forces applied to a disc cutter and the resultant stress on the cutter were considered. The maximum debris size encountered in tunnel excavation was also discussed assuming that it followed the Gumbel distribution. The results suggest that the proposed approach based on Nishimatsu's equation shows potential for future study.
Highlights
The debris expelled by a tunnel boring machine (TBM) varies widely in size and shape under the influences of many factors [1]
In the present study we investigate the size and shape of debris using Nishimatsu’s expression for cutting resistance [7], which is the most widely known expression among those dealing with rock cutting
Nishimatsu assumed, that p reached a maximum value at point A and diminished monotonically at points closer to B. He approximated this change with the following equation: Size and Shape of TBM Debris Estimated by the Nishimatsu's p where t is the cutting depth, is the angle between the horizontal axis and the shear plane AB, is the distance measured along the shear plane from the origin A, and n is a constant determining the distribution of the resultant force distribution. p0 is determined by force equilibrium and is proportional to F
Summary
The debris expelled by a tunnel boring machine (TBM) varies widely in size and shape under the influences of many factors [1]. Is the angle F makes with a vector normal to the rake face and is measured in the counter-clockwise direction Both Merchant and Nishimatsu assumed that fracture occurs on the shear plane (AB) in Fig. Nishimatsu assumed, that p reached a maximum value at point A and diminished monotonically at points closer to B He approximated this change with the following equation: Size and Shape of TBM Debris Estimated by the Nishimatsu's p. Krystof’s Assumption: A simple and clear proposal, this assumes that the shear plane occurs at a 45o slope relative to the resultant cutting force F. This assumption considers the shear planes occurring in a material with a small internal friction angle during a uniaxial compression test
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