A case study on defining rock damage threshold has been conducted by discrete element method. The threshold was then used for determining the sphere of blast influence at a nuclear power plant in China. First, the initiation and propagation of microcracks in rock specimen during uniaxial compression test has been investigated. The whole process, i.e., from crack initiation to specimen failure, was divided into four typical stages. At each stage the mechanical properties and deformation characteristics of rock specimen have been analyzed in detail, through which a damage threshold of Dcri=0.17for the welded tuff at current site was proposed. On the basis of this definition, the critical percentage speed variation of sound waves (PSV) through rock mass can be given by ηcri=9%. Thus, the sphere of blast influence can be determined and therefore, the integrity of preserved bedrock can be appraised. The current study provides a theoretical basis for sound wave test technology. It’s observed that, in a cylindrical charge explosion, the radius of rock damage zone is about 3 times of the depth, and the adverse effects of blasts attenuate much more rapidly downwards than horizontally.
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