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The microparameter calibration of the particle flow parallel bond model (PBM) is mostly based on a uniaxial compression test. The microparameters calibrated only by uniaxial compression tests cannot be directly used to study the mechanical properties of rocks with surrounding pressure conditions. To analyze the relationship between the macroparameters and microparameters in the model and select appropriate particle flow model parameters, this study conducted a particle flow numerical simulation experiment based on the basic test principles of the uniaxial compression, Brazilian splitting, and triaxial compression tests. An orthogonal experimental design was performed for the calibration of the microparameters of the particle flow PBM, and multifactor analysis of variance was used to screen out the factors that have a considerable influence on the experimental indicators. Regression analysis was performed on the significant influencing factors and test indicators, and the corresponding linear and nonlinear relationships between the macroparameters and microparameters were obtained. Lastly, the microparameters of the model were determined in accordance with the macroparameters of the mechanical test of the Barun open-pit mine dolomite, and a numerical simulation test was conducted. Simulation test results were consistent with the actual test results, thus providing a basis for a subsequent numerical simulation study on the mechanical properties of dolomite. [ABSTRACT FROM AUTHOR]

In view of the near slope blasting in Barun open-pit mine, which has merged sublevel mining, the operation safety conditions of middle-sized and large equipment in the second phase expansion are poor and need urgent improvement. To increase the efficiency of expansion and reduce costs, a 24-m-high bench and large spacing parameter for loosening blasting are proposed. The analysis of the physical mechanism of the stress wave attenuation in the rock indicates that the cylindrical charge is equivalent to several spherical charges. Considering the pressure attenuation, reflection, transmission, and superposition of the spherical charge after the equivalence, a double exponential function correction equation of the stress wave attenuation is obtained based on the Mises strength criterion. The stress of any point in the rock medium with various spacing parameter is obtained by calculation. ANSYS/LS-DYNA was used to simulate and study the stress distribution of a 24-m-high bench with various spacing parameter. Meanwhile, the accuracy of the correction equation was verified. The parameters of the high-bench blasting with good effect and low cost were determined to be 15 m × 5.5 m, and field tests were carried out. Results show that the large spacing parameter for 24-m-high bench loosening blasting in Barun open-pit mine is efficient and economical in medium-hard rock blasting. This study provides a reference for the practical exploration of the expansion of high benches in open-pit mines in China. The calculation error of the corrected double exponential function is near the numerical simulation result. It is suitable for all kinds of professional designers. [ABSTRACT FROM AUTHOR]

Millisecond-delay blasting in an open pit is difficult because the development of rock mass horizontal layering and mechanical properties vary widely among rocks. An unreasonable delay time for varied holes and rows often causes poor blasting effects. In this study, the multi-layer rock blasting model in the ANSYS/LS-DYNA software is used to optimize the delay time between holes and rows, improve the blasting effect, and reduce the vibration produced by blasting. The delay time for varied holes and rows is simulated. In line with the evaluation model of the entropy weight method, the maximum effective stress in the three sections is analyzed. The weight coefficient of each index is determined with entropy information theory, and a rock damage model is established. The ratio between the maximum tangential stress of the surrounding rock and the uniaxial compressive strength of the rock and the ratio of the uniaxial compressive strength of the rock to its tensile strength are selected as evaluation indicators. The maximum effective stress in the three sections at different positions between holes and rows is determined and analyzed. The test indicates that the delay time combination of 28 and 100 ms is effective and can avoid the interference of various geological conditions on the blasting effect. In accordance with the evaluation results, this delay time combination is used for field tests. Results demonstrate that the blasting effect of the selected delay time combination is remarkably enhanced, the boulder frequency is low, and the vibration caused by blasting is reduced by 30%. In special geological conditions where the mechanical properties of rocks differ greatly, the evaluation model of the entropy weight method presents crucial advantages in the precise selection of millisecond-delay intervals for horizontal layering bench blasting. [ABSTRACT FROM AUTHOR]