"This investigation was performed to determine the burden at which hard rock would break utilizing decoupled and unstemmed charges when the free surface parallel to the borehole was the wall of an open hole. This open hole was created by burn cuts and by drilling holes of 7-7/8 in. and 12 in. diameter. Additional tests were performed using partially stemmed charges where the stemming was the same size as the explosive charge.
The explosive used was a 0.75 lb. slurry charge, 1.5 in. diameter and 10 in. long. The diameter and depth of the borehole were 2 in. and 3 ft., respectively. The borehole pressure, Pb, for cylindrical charges was found to vary with the explosion pressure, P3, and the ratio of the radius of the charge Rc, to the radius of the hole Rh, by the relationship:
Pb = P3 (Rc/Rh)5
This equation relates the borehole pressure and the explosion pressure for the symmetrical decoupled condition.
For the non-symmetrical decoupled condition the average borehole pressure obtained for top, side, and bottom holes around a central opening was 57%, 35% and 11.5% of P3 respectively, with a decoupling ratio D = Rh/Rc = 1.33. The reflection theory of rock breakage was used to determine the decay exponent, m, in the transition zone and from the experimental data, the maximum burden Rtmax was found to be a function of the radius of the hole, Rh, the radial stress in the rock at the boundary of the cavity, Pmo, and the tensile strength of the rock, σt. These quantities are related by the equation
Rtmax = Rh/2(Pmo/σt)1/m
with 1/m = 0.66, 0.71 and 0.84 for top, side, and bottom holes, respectively. The burden as a function of the diameter of the opening, Φ, for side holes was determined to be of the form:
RΦ = Rtmax (1-3-0.41Φ)
The relationship between burdens, for partially stemmed Rt and unstemmed conditions Rt1 depends on the exponential decay time τ and τ1 and by the equation
τ / τ1 = Rt / Rt1
which was found to have a value of 1.113 in this investigation"--Abstract, pages ii-iii.
Rollins, Ronald R.
Haas, Charles J.
Clark, George Bromley, 1912-
M.S. in Mining Engineering
University of Missouri--Rolla
vii, 59 pages
© 1975 Roberto Ucar, All rights reserved.
Thesis - Open Access
Print OCLC #
Link to Catalog Record
Ucar, Roberto, "Decoupled explosive charge effects on blasting performance" (1975). Masters Theses. 3034.