An investigation into the effect of varying joint aperture and nature of surface on pre-splitting

Conference · Sun Dec 01 04:00:00 EST 1996

OSTI ID:398384

Tariq, S M; Worsey, P N ^[1]

---

1. Univ. of Missouri, Rolla, MO (United States)

Presplitting is now a universally accepted perimeter control technique in rock excavation. The success of presplitting and the smoothness and integrity of the resulting perimeter is largely dependent on the nature of joints in any given formation. Many facets of jointing have been previously investigated. The results of the effects of joints frequency and spatial positioning were presented by the authors at the ISEE annual meeting last year. This paper includes the results of further research into the mechanism of presplit blasting being carried out at the Rock Mechanics and Explosives Research Center of the University of Missouri-Rolla. The results of experimental model testing carried out in concrete blocks are presented. The research comprised of modeling both closed and open joints between 3/8 inch blastholes loaded with 15-grain per foot PETN detonating cord. The closed joints were (a) simple (rough) machine-cut and (b) surface ground (smooth-matching). The precision ground joints were modeled to simulate tight fractures as found in real rock mass. Precision spacers of varying thicknesses were used to create opening between the joint surfaces. It was found that precision ground joints have no significant effect on the maximum blasthole spacing up to two joints, and act like a continuous medium. This is because ground surfaces provide a relatively perfect match thereby transmitting most of the energy through the joint. However beyond two ground joints, the effects of attenuation is evident and the maximum blasthole spacing has to be reduced to obtain a presplit plane. A simple machine cut joint, on the other hand, has some undulations that results in loss of energy, making it necessary to bring the blastholes closer to achieve a presplit plane (for up to two joints). It was observed that a ground joint with spacer thickness of 0.012 inch behaves like a free surface.

• OSTI ID: 398384
• Report Number(s): CONF-960234--
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
EXPLOSIVE FRACTURING
FRAGMENTATION
FUNCTIONAL MODELS
GEOLOGIC FRACTURES
PERFORMANCE
PROCESS CONTROL
RESERVOIR ROCK
ROCK MECHANICS
SCALE MODELS
SURFACE PROPERTIES