Experimental and numerical investigation on the peak value and loading rate of borehole wall pressure in decoupled charge blasting

Decoupled charge structures are widely used in contour blasting because of their lower peak value and loading rate of the borehole wall pressure (BWP), which plays an important role in the contour blasting effect. The filling medium and decoupling ratio are the two key factors of decoupled charge blasting, and their effects on the peak value, rise time and loading rate of BWP need to be investigated. In the present study, physical model tests of decoupled charge blasting on cement mortar blocks (400 × 400 × 200 mm) were conducted under different filling mediums and decoupling ratios, and polyvinylidene fluoride (PVDF) gauges were used to directly measure the BWP. In addition, a numerical model was developed and verified to simulate the same decoupled charge blasting tests and some other tests with additional decoupling ratios. The measured and simulated results both showed that the peak value and the loading rate decreased with increasing decoupling ratio. Compared with the theoretical formulas, the modified power function formulas provide more accurate peak values. The peak pressure, rise time and loading rate were higher in water-coupled blasting, and the ratio of the peak pressure in water-coupled blasting to that in air-coupled blasting was between 2.35 and 4.28 under decoupling ratios of 2∼5. When the peak pressure was the same, the loading rate in the water coupling blasting was always lower than that in the air coupling blasting.