Information concerning size and shape of TBM debris is essential for designing the efficient loading, hauling and dumping system in TBM excavation. The information is also very important to decide how to recycle the TBM debris. However, only very limited information is available at present, and then theoretical or calculation method to estimate size and shape of TBM debris is still open to discussion.
In this paper, size and shape of TBM debris are estimated by the well-known Nishimatsu's equation that is usually applied to a roadheader or a shield type machine with chisel bits. In this study, the equation was applied to TBM excavation with disc cutters in which shear failure or plane extends from a new groove to an adjacent one. Estimated size and shape of TBM debris were found to be consistent with the measured results. Side force applied to a disc cutter and the resultant stress on the disc cutter were discussed. The maximum debris size encountered in tunnel excavation was also discussed assuming that it followed the Gumbel distribution. It can be said that the proposed approach based on the Nishimatsu's equation indicated a promising results for future extension.
