Experimental Evaluation of Fragments from TBM Disc Cutting under Different Load Cases
The Tunnel Boring Machine (TBM) tunneling process always contains a certain degree of vibrations due to the step broken phenomenon of the cutting tools. Undoubtedly, there is a quite difference in the fragment characteristics which are related to the construction efficiency of TBM under the static load and the combination of static and impact load. In this study, a series of rock breaking tests with a 216 mm diameter disc cutter and marble samples were conducted under different load cases. Based on the Rosin–Rammler distribution curve, the fragments from the cutting tests were also sieved to calculate the absolute size constant (x’) and coarseness index (CI). The relationship between coarseness index, absolute size parameter and the cutting parameters, specific energy, production rate was evaluated. The results show that there is an increasing trend of x’ and CI with the increase of cut spacing and penetration as well as adding impact load component. An overall downtrend in specific energy and upward trend in production rate which are associated with the high efficiency can be observed with the increasing CI and x’. It is believed that the conclusions are of great significance for improving TBM construction efficiency and cutterhead design.