Experimental and numerical study on the indentation behavior of TBM disc cutter on hard-rock precutting kerfs by high-pressure abrasive water jet

Tunnel boring machine (TBM) excavation of high strength or highly abrasive rock strata has some limitations, such as slow advance speed, low rock-breaking efficiency, and significant increase in the disc cutter changes and construction cost. To improve the rock boreability, a novel breakage method for hard rocks using a TBM disc cutter penetrating into kerfs precut by a high-pressure abrasive water jet is explored. With a confining pressure of 5 MPa, a series of cutter indentation tests and particle flow simulations of granite with two precutting kerfs are carried out to investigate the indentation behavior and the breaking efficiency. The effects of the kerf depth and the kerf spacing on the normal indentation force, rock chip volume, and specific energy are studied. The initiation, propagation, and coalescence modes of the surface and internal cracks and the failure mechanism are analyzed. The results show that the average peak force decreases significantly with the increase of the kerf depth, and the maximum rock chip volume and minimum specific energy are obtained at a kerf depth of 18.14 mm. The failure mode of kerf specimens after two indentations could be divided into the flat and slow shallow failure, one-sided inclined failure, and two-sided inclined failure. The micro-crack distribution of a single shallow kerf under low confining pressure is similar to that of intact rocks, while it is oblate and semi-elliptical under high confining pressure. However, for a single deep kerf, the breakage consists of a wedge-shaped crushed zone, a failure zone, and a damage zone around the kerf boundary and the bilateral inclined cracks, which are almost not affected by the confining pressure.