Study on interaction between TBM cutter and assisting kerfs based on full-scale cutting tests

When tunnel boring machines (TBMs) excavate intact high-strength rock masses, creating kerfs on the tunnel face is a promising solution to enhance the efficiency of TBM cutters. The cutters can be arranged to cut between kerfs or cut along kerfs. The rock breaking mechanism of cutting along kerfs is not fully revealed yet, and a quantified comparison in cutting performance between the two arrangements is needed. This study investigated the rock breaking mode and efficiency of cutting along kerfs by linear cutting tests. Different combinations of kerf depth (D) and cutter penetration (P) were designed. Cutter force, vibration, muck characteristics and rock breaking specific energy were analyzed. The results revealed two distinct modes existed in cutting along kerfs. Grooving mode occurred when P was 2 mm or when D was twice P, the kerf facilitated the formation of a thick crushed zone while constrained the expansion of lateral cracks, the kerfs were enlarged into grooves, producing much rock powder, the cutter force and vibration were significantly reduced compared to cutting without kerfs. Chipping mode occurred when D was not greater than P, macro cracks accumulated and extended to the bottom of the adjacent kerf after multiple layers of cuts, producing large rock chips, although the cutter force and vibration were higher than those of the grooving mode, the specific energy was significantly lower. The performance parameters of cutting along kerfs were compared with those of cutting between kerfs from another research. The rock formation in the chipping mode was less efficient than cutting between kerfs, while the cutter force and vibration in the grooving mode were significantly lower. Consequently, a conceptual cutterhead design for kerf-assisted cutting was proposed, which combined the advantages of the two cutting arrangements. The study contributes to the development of a new generation of kerf-assisted TBMs.