Simulation And Experimental Study On Crack Propagation And Control Of Peripheral Hole Blasting Around Tunnel

The cartridge often forms an eccentric decouple charge on the side wall of the contact hole due to gravity in roadway excavation smooth blasting. Eccentric decouple charge blasting can cause broken cell walls of the rocks and produce ultra-digging phenomenon, affecting the stability of surrounding rocks. In this paper, under the background of Dadingshan mine blasting, theoretical eccentric decouple charge blasting cracks, rock damage and control analysis and simulation experiment were carried out with plexiglass and cement mortar being the test media in different locations and decouple coefficients, as well as considering whether the wall is variable. The results are as follows:First, we analyzed the crack spatial expansion with stress wave interference theory, and found cracks of roof hole eccentric decouple charge could cause eccentric phenomenon. Meanwhile, the curve of correlations between decouple coefficient and maximum hole spacing was calculated.Second, we explored the crack distribution and propagation in eccentric decouple charge blasting and eccentric wall blasting with different decoulple coefficients, taking plexiglass(thickness of 10mm) as the test medium. The results showed that optimal outcomes were achieved when the side wall hole eccentric decouple coefficient was 1.76 and the roof hole eccentric decouple coefficient was 2.06. Compared with eccentric decouple charge blasting, eccentric wall blasting produced a larger ratio of layer cracks and surrounding rock cracks, which indicated that the wall casing could effectively control the crack propagation.Third, rock damage in eccentric decouple charge blasting and eccentric wall blasting with different decouple coefficients was studied with cement mortar as the test medium. It showed that the rock damage decreased as the decouple coefficient increased, with a minimum damage at K=2.0. In the experiment for side wall hole, the reduction rate of sonic waves was 17% lower in models with walls, compared with that in models without walls; under the same conditions, the reduction rate was 8% lower in models with walls in the experiment for roof hole.Finally, we made some suggestions on the improvement of Dadingshan mine blasting effect: optimize the hole spacing, change the eccentric charge location, select the proper decouple coefficient and apply the wall structure.