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Case study: Mechanism and effect analysis of presplitting blasting in shallow extra-thick coal seam

Sun Qiang, Shan Chegfang, Wu Zhongya, Wang Yunbo

Archives of Mining Sciences

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2022

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Vol. 67, no. 3

381--399

EN

The caving effect of the top coal caving is crucial for efficient mining. Using the Yushuling coal mine, Xinjiang province, China, as a case study, the coal and rock physical and mechanical parameters, such as the compressive, tensile, and shear strength values and hardness of the top coal and roof rock, were determined. The analysis of the effect of different factors on the blasting presplitting process was numerically simulated, and the optimal parameters of blast drilling were identified. Three presplit boreholes were implemented: in the workface, the workface’s advance area, and the two roadway roofs in the workface’s advance area. The optimal blasting drilling parameters and charge structure were designed. The field test results in the mine under study indicated that the top coal recovery rate of the 110501 fully mechanised top coal caving face was improved twice (from 40 to more than 80%), and an effective blasting presplitting was achieved. The proposed blasting presplitting method has an important guiding significance for fully mechanised top coal caving mining in Xinjiang and similar mining areas.

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Mechanical responses of igneous rocks to microwave irradiation: a review

Bai Guogang, Sun Qiang, Jia Hailiang, Ge Zhenlong, Tang Liyun, Xue Shengze

Acta Geophysica

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2022

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Vol. 70, no 3

1183--1192

EN

In order to explore the mechanism of microwave radiation damage to rocks and improve the efficiency of underground rock fragmentation, statistics have been conducted for nearly 40 years, and the heating effects of four types of igneous rocks (granite, basalt, syenite, and gabbro) after microwave irradiation have been analyzed. The attenuation of tensile and compressive strength, and the microwave response mechanism of igneous rocks are studied. The results show that under microwave energy of 0–50 kJ, the tensile and compressive strengths of rock do not change significantly; however, above 50 kJ, they decrease rapidly. With increasing contents of Fe-rich minerals in rock, such as pyroxene, microwaves have a greater fracturing effect, which is manifested as rapid attenuations in tensile and compressive strength. The wave velocity damage factor and tensile strength damage factor of igneous rocks increase with the increase of microwave energy.

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Efects of high-temperature thermal treatment on the porosity of red sandstone: an NMR analysis

Zhang He, Sun Qiang, Jia Hailiang, Dong Zhihao, Luo Tao

Acta Geophysica

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2021

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Vol. 69, no. 1

113--124

EN

High temperatures afect the physical properties of red sandstone seriously, especially the pores. Understanding its mechanism is of great signifcance in coal mining following underground gasifcation, geothermal energy utilization, and the deep burial of nuclear waste. Nuclear magnetic resonance (NMR) was used to detect pore structure characteristics, and scanning electron microscopy (SEM) and polarizing light microscopy (PLM) were used to mechanism of change. The transverse relaxation time (T2) and signal strengths of red sandstone treated at various temperatures were observed by NMR, and then, the pore situation can be obtained, and fnally, the infuence of temperature on the pore structure of red sandstone can be obtained. Microscopic photographs of the pores of red sandstone were obtained by SEM and PLM to assist in explaining the process of microstructural change, especially the infuences of temperature on pore characteristics and grain morphology and distribution. The researches indicate that after the heat treatment of red sandstone at 25–1300 °C, the pore and strength characteristics change in well-defned stages. Before 500 °C, the pore diameters and distribution range increase, but the porosity and internal grain structure do not change signifcantly. At 500–1000 °C, red sandstone micropores contract, mesopores and macropores develop, and strength decreases. After 1000 °C, the grains that comprise sandstone melt and fll many of the pores, decreasing porosity. The proportion of micropores decreases, while mesopores and macropores increase. In addition, a large number of bubbly holes appear in and on the sandstone, presumably caused by gases such as CO2, and water vapor from dehydrating grains. The changes in pore and cementation states with temperature are the main factors afecting the tensile strength of red sandstone.

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Analysis of the characteristics of magnetic properties change in the rock failure process

Zhang He, Sun Qiang, Zhenlong Ge

Acta Geophysica

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2020

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Vol. 68, no. 2

289--302

EN

It is difcult to observe changes in the internal structure of natural rocks when under certain pressure ranges. However, such rocks have specifc magnetic properties that are established during their formation process. Through studying changes in their magnetic properties while under pressure, which are readily observed and analyzed, as combined and contrasted with their associated structural changes, the relationship between the stress–strain and the magnetic feld intensity can be established. Based on the stress–strain and magnetic feld strength data obtained from the relevant literature, the process of rock and rock-like mechanical failure can be divided into three stages: elastic, plastic, and rupture. The performances of diferent rocks during these stages were analyzed, and there was an obvious transition point between any two adjacent stages. Thus, this study provides theoretical support to establish the relationship between structure and magnetic variations of rocks and rock-like bodies.