| In underground blasting, the pull of the initial cut is the limiting factor for the success of the rest of the round. By improving the pull of the first cut, a critical step is made towards improving the entire round. This project attempted to optimize a burn cut's effective pull by varying the depths of the relief holes in the burn, and then analyzing the results. In testing, relief holes were drilled to depths both shorter and longer than that of the cut's charged holes. The overall objective was to consistently achieve greater pull than in a standard burn, using an identical amount of explosives. Increased pull results in savings of both time and cost in underground heading advance.;The testing was conducted in dolomitic limestone at the Missouri S&T Experimental Mine. The project utilized a small diameter hole burn design that has historically proven to be successful in the rock type in which the tests were being completed. Burn cuts were drilled and shot separate of the full standard round. This allowed for the author to analyze depth of pull solely in respect to the initial cut holes. Drilled with a jackleg and a design template, identical replications of the cut were tested and pull measurements were obtained.;With all testing completed and results analyzed, the data suggests that a depth of pull greater than the length of the longest charged hole can be achieved through the application of lengthened relief holes. The tests consistently show an average pull increase of 3 inches, which results in an average pull of 105 percent in the rounds. The findings produced by this project should prove beneficial for work performed in similar blasting conditions as well as in various rock types and other burn configurations. |
