Shigen-to-sozai, Vol.116, No.11, pp.894-900.
Mechanism of Chipping upon Water Jet Drilling
in Rock
Katsuhiko SUGAWARA1, Akira SATO2 and Takayuki HAMAURA3
| 1. Graduate School of Science and Technology,
Kurnamoto University, Kurokami, Kumamoto
860-8555 2. Faculty of Engineering, Kumamoto University 3. Tokyu Construction Co., Ltd. |
| A specific fixed depth chipping experiment is conducted to investigate the mechanism of chipping upon water jet drilling in rocks. It is shown that the net impinging time: t for a fixed depth chipping is closely associated with the bottom incident pressure: p evaluated by the Third Power Method, and that the fixed depth chipping occurs in the case that the bottom incident pressure: p is greater than a thresholding pressure: pth,. The relation of p - t determined by the experiment is explained, basing on the fracture mechanics, and it is discussed that the chipping upon drilling is a kind of the fatigue fracture and initiates at a circumfereace of the advancing bottom. In order to forecast the incidence of the chipping upon water jet drilling, a chipping potential is subsequently proposed as a function of p and pth It is clarified that the chipping potential Pc in the case of p = Pth = Se, where Se: the erosion strength of materials, is available for forecasting the incidence of chipping upon drilling. |
| KEY WORDS: Water Jet, Erosion, Chipping, Drilling, Rock, Fracture |