| This thesis discusses the development of a continuum damage model and its applications to the analyses of the following theoretical and practical problems: (1) the mechanisms involved in rock fragmentation by blasting, the examination of the spherical charge cratering theory; (2) the blasting effects of air decked/decoupled explosive charges and (3) the influence of accurate timing on the rock fragmentation processes and blasting results.;The damage model is developed using a continuum approach to treat the rock material and a statistical approach to describe the effects of the micro crack system. Rock damage is defined as the probability of fracture at a given crack density. An algorithm is integrated into the model for fragment size prediction. The model has been calibrated by field tests and it is elucidated that its implementation in a wave code is applicable for both damage and fragment size modelling.;In studying the fundamental mechanisms in rock blasting, the model is used to provide a satisfactory description of the formation of a crater in an axisymmetric environment. Some important numerical findings such as the existence of a pressurized ring prior to tensile failure are presented. Examination of the spherical charge cratering theory using the damage model shows that, for an explosive charge, a length/diameter ratio of 1 is not the optimum and the gravity center is not the best initiation point. The optimum range of ratios and the position of the best initiation point under the modelling conditions are obtained.;To analyze the effects of air decking/decoupling, the movement of the detonation products in an air chamber is modelled. It is revealed that such movement is responsible for the formation of a series of secondary loading waves and the release of the energy retained in the detonation products. The simulation results show that, when a top air deck longer than a minimum beneficial length is used, the blasting results are improved. The energy relationships in air decking are examined and it is demonstrated that, in maximizing explosive energy utilization, the use of an air deck is more important for non-ideal explosives than it is for some more ideal explosives.;The study of the effects of accurate timing conducted using the damage model shows that stress wave collision or superposition in the rock mass does not benefit rock fragmentation. Wave collision created by accurate detonators tends to result in poor distribution of the explosive energy in the rock burden. While wave superposition may produce a larger volume of fragments, it is accompanied by less satisfactory fragmentation. It is concluded that, for rock blasting purposes, delay detonators having an accuracy in microseconds do not have any advantage. Instead, millisecond accuracy is sufficient to achieve optimized rock fragmentation. |
