Experimental investigations of direct measurement of borehole wall pressure under decoupling charge

Decoupling charge is quite widely applied in smooth blasting, pre-splitting blasting, and bench blasting. The borehole wall pressure (BWP) is an indispensable condition for analyzing blasting action as it is the main initial parameter that determines the stress wave generated in the rock. In this study, a full-scale concrete model (4.0 m in length x 3.0 m in width x 1.6 m in height) with two boreholes was utilized to directly measure the BWP under decoupling charging. PVDF (polyvinylidene fluoride) gauges were employed as pressure-sensing devices to develop a technique for direct measuring high dynamic pressure due to its superior characteristics. The values of measured peak pressures of the borehole wall ranged from 1461 to 205 MPa within 0.1-1.1 m from the explosive charge end along the borehole axis. BWP of decoupling charge are responses to air shock wave loading and explosion gas loading, in which the responses near the explosive charge are the results of air shock wave and explosion gas working together, while the responses far from the charge are merely loaded by the air shock wave. The strain rates varied from 2.12 to 0.73 s(-1) for the test range, which has confirmed that decoupling blast loading is a quasi-dynamic process. By fitting the experimental data, it is found that the peak value of BWP along the borehole axis decreases as a power function with the increase of the distance from the explosive. The findings may be of great significance to mechanism analysis of rock blasting, scientific design of blasting schemes, and numerical simulation of rock blasting.

Automated summary

This study measured the borehole wall pressure (BWP) under decoupling charging using a concrete model. The experiment confirmed that decoupling blast loading is a quasi-dynamic process, and the peak value of BWP decreases as a power function with the increase of the distance from the explosive.