FRACTURE-MECHANICS APPLICATIONS TO DRILLING AND BLASTING

This paper gives a brief review of research in rock fracture mechanics as conducted at the Fracture and Photo-Mechanics Laboratory (FPML) at Vienna University of Technology. The mechanisms pertaining to percuss ion drilling and blasting are investigated, with specific reference to the application of fracture mechanics. In order to gain an improved u nderstanding of the mechanisms controlling rock fragmentation, a multi disciplinary approach is followed which includes laboratory experiment s conducted in plexiglass and rock, in-situ held experiments and analy tical/numerical modelling techniques. Field experiments revealed that percussively drilled holes exhibit a very shallow region of damaged ro ck. An analytical model to simulate damage accumulation and crack init iation due to elastic waves generated by impacting drill bits was deve loped. This model, based on damage and fracture mechanics, was incorpo rated into a numerical finite difference code. Fracture and damage mec hanics parameters are related to the moment tensor which is determined experimentally by means of acoustic emission. Small scale model blast s were used to investigate the blast-induced fractures in the near-bor ehole zone as well as in the far held. Analytical and numerical invest igations give insight into stress wave and gas driven fracturing. The applicability of the dynamic finite difference program SWIFD to the in teraction between stress waves and cracks is illustrated.