An Investigation into the Performance of Bottom Air-Deck Method in the Presence of Water, Using SPH-FEM

The use of the bottom air-deck method in open-pit blasting has been widely accepted by researchers as an efficient technique. In this method, leaving an empty space (air-deck) at the bottom of the blast hole improves the blast results. However, if the blast hole is filled with water, the presence of water may affect the blast results. In such cases, it is necessary to study the effect of the water in the air-deck area on blasting performance. In this research, a numerical method was used to investigate the effect of the presence of water in the blast hole on the blasting results in the bottom air-deck method. Considering the advantages of the SPH method in modeling the fractures caused by blasting and the advantage of the FEM method in terms of processing time, the combined SPH-FEM method was used to carry out the simulation. The Dehghan-Banadki empirical model was employed to validate the model and determine the SPH parameters. The results showed that due to the incompressibility of water, more pressure produced by the explosive detonation is transferred to the rock, Additionally, water causes attenuation of the blast wave and reduces the wave frequency. In a dry blast hole, despite the decrease in the initial wave pressure compared to a water-filled blast hole, multiple reflections of the wave in the empty space lead to longer duration waves and absorption of explosive energy by the rock. The peak effective stress taken at different distances around the blast hole in the air-deck area showed that the maximum stress applied to the rock in the water-filled blast hole is higher. The results also indicated that the total length of fractures in the dry blasting condition is 13.15 m, while in the water-filled blast hole blasting, it is 12.5 m. Therefore, the total length of fractures in the dry blast hole is only 5% more than in the water-filled blast hole. In other words, the presence of water in the air-deck area does not have a negative effect on the blasting results, and thus, this method can also be used in water-filled blast holes.