Mostafa Sharifzadeh

Evaluation of air blast parameters in block cave mining using particle flow code

Abstract Air blast, a sudden mass movement of air, can occur in underground mining system where caving develops an extensive mass of unsupported rock spanning a large void. Air blast can result in injury to mine personnel, damage to equipment or disrupts mine operation. Evaluation of air blast parameters is, therefore, an essential part to develop strategies to mitigate the hazard. The properties of a muckpile or a caved zone are significant factors affecting the magnitude of air blast in particular on the undercut and extraction levels. This research investigates the effect of muckpile properties on air flow using the numerical code, PFC2D. The critical parameters such as thickness, block size and porosity (swell factor) of the muckpile have been studied to quantify how much they could change the magnitude of air pressures and velocities while the air flows through the muckpile. It was found that the porosity of the muckpile is the most effective parameter on the magnitude of air blast and by designing a thick layer of blasted rock with low porosity in the caved zone, the intensity of the air blast can be significantly reduced. The findings of this study can be used to design air blast plugs or bulkheads in order to isolate any potential air blast from the active workings, or to quantify the minimum thickness of the muckpile above extraction levels to manage air blast hazards.

Size-dependent compressive strength properties of hard rocks and rock-like cementitious brittle materials

Abstract Rock engineering projects have always been constructed on different (from micro to macro) scales. This makes understanding rock behaviour at different scales essential. In previous statistical studies on igneous hard rocks, the correlation of uniaxial compressive strength (UCS) values in different diameters with estimations of specimen size effect models was weak. In view of this knowledge gap, the present research proposed a model of appropriate size effect in igneous hard rocks. This research also aimed at discussing the effect of specimen size and grain size on the UCS of concrete specimens. To achieve these aims, studies were conducted in parallel on the previous and new experimental data. Non-linear regression analysis on igneous hard rocks indicated that there is a better agreement between the outputs of the multi-fractal scaling model and the specimen size effect model using the fracture energy theory and the results of previous laboratory tests. In addition, in the experimental study, the grain size effect on the predictions of specimen size effect models was exhibited. The results of this research can be used for designing engineering projects at different scales.