Proposing feasible borehole spacing in non-vibrational rock splitting method using discrete element modeling

Abstract

Drill-and-blast method is widely used for tunnelling and trench at the cost of noise and dust production alongside because of the excessive vibration used for excavation in urban areas. These problems demand utilization of a non-vibrational rock splitting method that involves the breaking of rock blocks by inserting a split-wedge system mounted on an excavator into already drilled boreholes and splitting of rock segments with their subsequent excavation. Particle mechanics approach using PFC2D code was selected for this numerical analysis based study due to its inherent function of crack formation and coalescence that could be related to the fracture propagation in rocks. The spacing between the drilled boreholes is usually kept to be 0.6 m in soft rocks. This study can prove useful considering the deficiency of research work in this area. In this study, various values of spacing between 1.4 m deep boreholes were investigated for geotechnical properties of different rocks by adjusting the micro parameters of particles using bonded particle model (BPM). Fracture propagation was achieved by inserting the full length (1 m) of the split-wedge system in the borehole and the results were obtained according to two different splitting widths of the system at the head of borehole. The numerical analysis results show that when the splitting action is performed in soft rock, a breakout zone is formed vertically from the rock surface to the tip of fractured plane approaching the free space. Based on the numerical analysis results, it is suggested that the borehole spacing values greater than those in practice can be used in soft, normal, and hard rocks if the splitting width of 20 mm and 25 mm is utilized, respectively. The application of the results suggested in this study can help undergo an economical and efficient excavation process as they shall not only reduce the noise production during borehole drilling as well as the time and power usually consumed for the excavation.