A Study of Millisecond Blasting on High Bench at Barun Iron Ore Operation

To improve the productivity and efficient of modern large-scale open-cut mines, a number of technologies are developed and trialed, including new blasting equipment, larger blasting holes, high benches, air spacing, and short-delay blasting within holes. However, the relative blasting parameters need field calibration and further investigation of theories on these techniques are required. This paper studied the open-cut bench blasting at Barun Eboxi Mine of Baotou Iron and Steel Group via theoretical analysis on shock wave, numerical simulation, and field test. According to the technical conditions of the site, three sets of vertical boreholes at 310 mm diameter were drilled on 24 m high batter; and three sets of air-spaced charges were set up. The digital electronic detonator was used to initiate at millisecond intervals. The study found that under the condition of 24 m high bench, the use of intermediate air interval is beneficial to the rock fragmentation. The delay time within the hole is 3-8 ms. The bottom of the lower explosives and the top of the upper explosives were devised for initiation to optimize the initiation location. The peak effective stress points are 63.6%, 52.2%, and 8.9% higher, respectively. The field test of high-bench intrahole millisecond blasting in Barun Eboxi mine shows that the intrahole millisecond blasting parameters proposed in this study are feasible.

Optimization and Application of Spacing Parameter for Loosening Blasting with 24-m-High Bench in Barun Open-Pit Mine

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.

Have Ferguson and Its Companions Contaminated Black Support for Legal Institutions?

Given that African Americans have been victimized by the abuses of individual police officers as well as by discriminatory public policies such as “stop-and-frisk,” it is no surprise that considerable alienation seems to characterize the contemporary relationship between African Americans and the legal institutions that govern them. But have those attitudes poisoned more general views of legal institutions such as the U.S. Supreme Court? Using a nationally-representative sample of African Americans, we assess whether blacks generalize from their experiences with local authorities to perceptions of legal system fairness, and further to institutional support for the high bench. While we find that perceptions of legal system fairness have not undermined Supreme Court legitimacy, all of the relationships we consider are found to be conditional upon the nature of group attachments.

Substantiation of the Technology of Efficient Transition to High Bench Stripping of Thick Coal Seams

One of the most promising areas of increasing the open mining efficiency with the methods reducing the negative impact on the environment is the use of high overburden benches, including those on the basis of the stripping system with overburden transport. The use of high overburden benches in the open mining of steep and steeply dipping deposits ensures the growth of the completeness the deposit's reserves mining while simultaneously increasing the safety and efficiency of open mining operations and reducing the surrounding environmental impact. The justification of the parameters and the technology of an effective transition to the high bench stripping of thick coal deposits is performed. It is proved, that the transition to high overburden benches in the period of maximum development of mining operations provides the increase in the volume of additional recoverable mineral resources by 18-23% corresponding to the increase in the depth of the open pit mine and the period of its operation. At the same time, the length of transport routes and communications is reduced to 15%, as well as the number of transport equipment and the time for the transfer of machinery and equipment.

Optimization Study on Stability of Dragline Stripping Bench and Mining Parameters of Dragline Stripping Technology

Heidaigou Surface Coal Mine (HSCM) is a large surfaces coal mine that first uses the throwing blasting - dragline stripping technology. Lots of new demanding prompt solution issues appears in HSCM without any successful experience in China, such as the stability of dragline stripping bench, the design and implementation of throwing blasting parameters, and the optimization of dragline stripping technology parameters. Rigid Body Limit Equilibrium Method (RBLEM) was used to study the safety and stability of dragline solid high bench and dragline stripping loosen bench under different workface parameters and influence factors. The safe operation parameters of dragline stripping bench are proposed. The dozer lowered height of the stripping bench, the width of extended bench and dragline operation parameters are optimized using the Optimization System of Dragline Stripping Technology (OSDST). The results can provide the decision support for HSCM.