Evolution law on explosive stress and strain field of column charges at middle detonation position

Combining dynamic caustics,ultra-dynamic strain test and numerical analysis method,the explosive stress & strain field of column charges with middle detonation and the evolution law of the stress field at the tip of the crack were studied. The conclusions obtained by the three analytical methods are consistent. According to caustic method, main stress differences of mid-perpendicular direction,end perpendicular direction,end axial direction and end tilt di- rection gradually decreased for middle position denotation,and the maximum values namely are 50. 9,29. 9,15. 3 and 13. 3 MPa,thus the end effect was obvious. As the explosive stress wave decreased rapidly,the differences of principal stress differences at the circular holes gradually decreased as the distances increasing. The small circular holes can effectively measure the influence of crack size and the range of influence. When the crack propagated to the circular holes,the stress field around the tip of the crack increased,and the caustic spot at the circular hole increased. As the crack propagated,the direction of caustic spots changed continuously. It was obtained by the ultra-dynamic strain test method that the strain duration in the column area of borehole was 40 μs,due to the superposition of stress waves, mainly representing compressive strain. The axial strain duration at the end of the borehole was 10 μs manifesting com- pressive strain,which converted to tensile strain and last for a long period. The numerical simulation shows the fitting curve of stress attenuation in four directions around the boreholes,which makes up for the defect that the experimental method cannot measure the evolution law of stress and strain field near the boreholes. The column charge with middle detonation significantly improves the uniformity of the explosive stress field along the axis of the boreholes,which is beneficial to the rock fragmentation,thereby improving the utilization of the boreholes and reducing the rock mass rate.