Wave propagation, damage evolution, and dynamic fracture extension. Part I. Percussion drilling

Abstract

Percussion drilling, wave propagation in damageable media, and the evolution of damage caused by repeated impacts during percussion drilling in brittle disordered materials are investigated. Analytic, numerical, and experimental works complementing each other in clarifying the complex dynamic process of damage evolution and fracture network development in polycrystalline brittle materials are presented. Rock samples from field tests were sectioned and a microscopic investigation of the damage and fracture zones at the bottom and circumference of the borehole was performed. On the basis of experimental findings, we develop a three-dimensional numerical simulation scheme which incorporates wave propagation in dissimilar granular arrangements, dynamic impact phenomena, and accumulation of brittle damage to the rock grains. The combination of brittle damage continuum mechanics with the theory of propagation of elastic wave proves to be a very suitable approach for the description of impact destruction of rock and rocklike materials showing brittle behavior. The developed 3D finite-block numerical code enables one to simulate single and multiple impacts on personal computers. Further development will include the impact of a sequence of bits and the implementation of time-varying elastic properties in the wave propagation model. The results of experimental field tests are in good agreement with numerical model simulations.