Theoretical and numerical investigation of deep-hole cut blasting based on cavity cutting and fragment throwing

Abstract

Cut blasting is the key of single-face blasting in underground rock engineering, which determines the success or failure of the blasting process. Traditional cut blasting is not suitable for deep-hole blasting engineering because of the difficulty of throwing rock fragments and the accumulation at the bottom. In this paper, an advanced concept of cavity cutting and fragment throwing (CCFT) for cut blasting is proposed, which is divided into the following two blasting processes: cut hole breaking and fragment-throwing hole throwing. By establishing a mechanical model of CCFT, cut cavity efficiency is introduced as an evaluation index of the cutting effect, and the advantages of CCFT cut blasting are analyzed theoretically. Based on the smoothed particle hydrodynamics-finite element method (SPH-FEM), a CCFT cut blasting model and a traditional cut blasting model are established and compared. The results show that the detonation of the central fragment-throwing hole in CCFT cut blasting plays a key role in the throwing of rock fragments, improving the cut cavity efficiency by approximately 20%. Additionally, 9 sets of numerical models are established to study the effects of various parameters on the cut cavity formation, and optimization suggestions are given for the parameters. The findings show that as the hole depth increases, more blasting energy is needed for the throwing of rock fragments, which can be effectively achieved by increasing the ratio of the charge weight δ. The hole spacing needs to be properly designed to ensure that the rock between the holes is penetrated and broken. The large-diameter fragment-throwing hole guides the development of blasting cracks and promotes rock fragmentation. Finally, two engineering cases, namely, one-step shaft excavation and deep-hole drilling and blasting in a rock tunnel, illustrate the application of CCFT cut blasting. The good application results provide references for similar engineering projects.