Abstract: Based on the principles of hole-by-hole millisecond delay initiation technique, the basic features of the burden distance distribution for the triangular drill pattern and the rectangular drill pattern are analyzed. The uniformity of the burden distances at the initiation instant is found to be strongly related to the type of drill pattern and has a significant impact on the amount and quality of fragmentation. The concept of the uniformity coefficients of burden distance distribution β, γ, and η are thus introduced. It is found through a comparative analysis that, with respect to the hole-by-hole millisecond delay initiation technique, the triangular drill pattern is superior to the rectangular drill pattern in getting a more evenly distributed burden distances in different directions. If a coefficient of hole spacing  =1.155 is adopted for the triangular drill pattern, the burden distances in all directions will be nearest to each other, being most favorable to the improvement of the fragmentation amount and productivity of blast holes.

Key words: Hole-by-hole initiation, Drill-hole pattern, Burden distance, Uniformity coefficients of burden distance distribution