Rock fragmentation using the disc tool assisted by the prefabricated kerf: Numerical modelling based on discrete element method (DEM)

Abstract

To improve the hard rock cuttability of disc tool and decrease its wear rate, a method of rock fragmentation with the help of the prefabricated kerf formed by external waterjet is proposed. Furthermore, a numerical model for rock/disc tool interaction based on the Discrete Element Method (DEM) is established to reveal the mechanism of rock fragmentation mechanism by disc tool and the effect of prefabricated kerf on rock fragmentation progress, and to investigate the cutting depth of disc tool, kerf parameters and their combination relationships with rock fragmentation performance. Firstly, the micro parameters of particles are calibrated by the uniaxial compression strength (UCS) test of the rock, and the cutting force signals in tests and simulations are compared, thus providing the effectiveness of the proposed model. Secondly, the rock/disc tool interaction mechanism is revealed by analyzing the cracks initiation and propagation microscopically and the variations in the cutting force macroscopically, and the cutting depth of disc tool under the optimal rock fragmentation performance is determined as 20 mm. Finally, the effect of different combinations of cutting depth and kerf parameters (including kerf depth and kerf spacing) on rock fragmentation is considered, and the results indicate that when the diameter of disc tool is equal to the kerf spacing, the rock can be deemed to be unconfined, and the cutting force decreases by more than 30 % compared with that of rock fragmentation without prefabricated kerf. The relationship between the cutting depth and the kerf spacing exerts a significant influence on the specific energy (SE), and the cutting depth and kerf spacing in the optimal case is 20 mm and 100 mm, respectively. The relationship between fractal dimensions of rock fragments and SE is also studied, with the SE increasing linearly with the fractal dimensions.