Study On The Rock Crack Mode Under The Cutting Of Disc Cutter By Linear Cutting Experiment

The high-radioactive waste repository and underground laborary has high standards for quality, accuracy and excavation damage control. Mechanical excavation methods (mainly by TBM) are higher in effeciency, lower in damage zone sacale and exvironmental friendly, and has been proposed as the major method for the excavation for tunnels in the repository. The rock fragmentation of TBM is implemented by the disc cutters on the cutter head, so the cutter-rock interaction is the fundamental problem to solve in order to understand the rock breakage and damage, and can provide basis for the following research on the mode of nuclide emission and transmission.In order to study the crack mode of Beishan granite under the indentation of a single disc rolling cutter, a series of linear cutting experiments were conducted on the Mechanical Rock Fragmentation Experimental Platform developed by Beijing University of Technology. During the experiment, a constant cross-section disc cutter with a diameter of17inches (432mm) is used and a block of Beishan granite with the size of1000×1000×600mm is adopted. After the tests, it is found that there is a cracked part beneath the groove with varied fragmentation degree. Based on the observed crack mode and crack density, the rock sample is classified into re-compacted zone, crushed and cracked zone and intact rock zone, then the size and area of these zones are summarized accordingly. Meanwhile ultrasonic velocity tests and rebound tests are conducted to obtain the properties of different zones. Finally, it is found that these testing results agree well with the fragmentation degree of different zones.Compared with the cutting of normal cutter, the cracks lean to the direction of the load under the cutting of inclined cutter, the crack density is also relatively higher at the very side. Besides, when the penetration depth is the same, the normal force of the normal cutter is significantly higher than the inclined cutter (2.5times), the depths of the zones stays similar (within25%), the width ofthe crater and the crushed zone (close to the rock-cutter contact position) while the width of the severely cracked zone and slightly cracked zone are significantly low. The ultrasonic velocity tests result also indicates that the velocity if drastically different in different zones, the size of corresponding zones changes as the setting changes, while the parameters in the zones are similar.The set joint spacing increases in the order of100,400,600mm, the penetration depth (or load) needed to generate the macro median cracks increase accordingly. This phenomena indicates that the joint intends to induce the initiation and propagation of macro median cracks, a smaller joint spacing will make it easier for the median crack to reach the next discontinuity surface, by then, chips generated will be extraordinarily large and be different in type from normal cutting. Smaller the spacing is, more obvious this tendency would be. At the same time, the underlying thin pieces of rock sample usually stay intact, despite the severely damaged upper ones, which means the joints also play an important role in protecting the underlying rock.In addition, under different experimental setting, the area of these zones changes significantly, while the properties of corresponding zones almost keep constant.