The urgency for developing new, effective methods of excavation of rock and ore in tunnels, mines, and other underground openings in rock is well documented (NAS Rept., 1958) (Lane and Garfield, 1972) (OECO Tunneling Conference, 1971). Two novel blasting methods offer promising developments for excavation of rock (Peterson, 1972) (E. I. DuPont de Nemours) (Rollins, et al, 1974), which are: (1) a spiral type of explosive round with a machine for remote control (Peterson, 1972), and (2) an automated system using decoupled charges (Rollins, et al, 1974). The spiral system (Peterson, 1972) utilizes a simulated auger geometry, blasting one hole at a time. Drilling, explosive loading, and blasting are to be performed by remote control. Rock throw is primarily perpendicular to the spiral face, the free face being parallel to the axis of the tunnel. A multiple heavy wire mesh barrier is employed to partially contain the fly rock. Blasting utilizing decoupled charges with an automated drill and blast machine has proven technically feasible (Rollins, et al, 1976). Automated explosive handling and blasting systems with protected personnel at a short distance from the face represent radically new procedures which will require careful evaluation for production and safety standards. More effective methods of tunnel excavation with explosives must minimize air blast, ground vibration, overbreak into the walls, and markedly reduce the disadvantages of cyclic operations. The small charge blasting system described below offers most of these advantages. The results of the first year's investigation have demonstrated a good degree. of probability for an effective rock breakage system with air blast reduction containment, fragment containment, reduction of wall fracturing, and reduction of ground vibration. The concept of controlled rock fracture by reinforced stress waves from simultaneously fired explosive charges was inspired by the results of experimental tests and theoretical analysis of the stress fields generated by adjacent thermal inclusions, and by mechanical rock splitters (Clark et al, 1971), as well as the processes of presplitting and smooth blasting, and by the photoelastic analysis by Dally (Dally and Khorana, 1971). The first year's work dealt with round design parameters, shield design and testing, measurement of fly rock velocity, ground vibration, and air blast reduction and fly rock containment by a steel shield. Small holes of 3/4 and 7/8 in. diameter and 20 in. depth were loaded with charges of 50 to 100 gm of 60% dynamite, which gave an optimum burden and spacing of 20 and 18 in., respectively, in granite. A rectangular tunnel 8 ft x 8 ft was employed to permit a simple design for the shield with a V-cut with peripheral holes closely spaced to give fracture control at the wall, floor and roof. Observations were also made of bit wear and small drill performance. For an operational system insensitive slurry explosives will be used instead of dynamite, and the smallest diameter of sensitized slurry is 1 in., requiring holes of 1-1/8 in. diameter.


Currently, the most flexible technique of excavating hard rock is the conventional drill and blast method. However, blasting operations are cyclic, utilizing large charges which generate high velocity fragments, create vibrations, air blast, and cause overbreak and fracturing of the surrounding rock.

This content is only available via PDF.
You can access this article if you purchase or spend a download.