Full-scale granite cutting experiments using tunnel boring machine disc cutters at different free-face conditions

This study presents the results of full-scale hard rock (granite) cutting experiments using tunnel boring machine disc cutters at different free-face conditions. Rolling cutting tests are conducted on a full-scale rotary cutting machine with a commercial constant cross-section disc cutter with a diameter of 432 mm. Three free-face conditions are prepared for the tests: vertical free faces, inclined free faces (with different heights and cut spacings), and narrow kerfs. The rock-cutting force, rock-cutting trajectory, specific energy, and shape of the representative rock chip are analyzed and compared for each test. The major results are as follows. First, for the granite subjected to vertical free-face conditions, the cut spacing should not be larger than the critical value of 140 mm in order to break the rock successfully with high efficiency. Second, the free face that is closer to parallel to the penetration direction exhibits a decreased rock-cutting force and improved rock-cutting efficiency. Third, narrow kerfs are not as effective as vertical and inclined free faces for assisting rock breaking. Therefore, to exploit the advantages of narrow kerfs, they should be prepared close to the cutting path, with spacings of less than 40 mm for the studied granite. Fourth, the applied grain-based discrete element method is effective for numerical analysis of the rock-cutting process because the rock-fragmentation performance is very similar to that in the laboratory tests.