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Study on pressure relief mechanism of hydraulic support in working face under directional roof crack

Zhang Jun, Liu Jianning, Wang Yajun, Yang Gang, Hou Shilin, Wang Yuanjun, He Manchao, Yang Jun

Archives of Mining Sciences

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2023

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Vol. 68, no. 1

103--123

EN

When mining coal from the working face, the main roof withstands the overlying strata. The main roof’s first weighting and periodic weighting may cause accidents, such as crushing the working face hydraulic supports. A mechanical model of the main roof was constructed, and the contributing factors of first and periodic weights on the main roof were examined in order to prevent such accidents. The thickness of the main roof was found as the most contributory factor to the main roof’s stability. Therefore, a new directional roof crack (DRC) technique is proposed, which produces directional cracks in the main roof through directional blasting and makes part of it collapse in advance so as to reduce the thickness and relieve the first and periodic weighting. To verify the effectiveness of DRC, the mechanism of DRC was analysed. A mechanical model of the hydraulic support was constructed, and the DRC techniques were tested on-site. Field experiments with a complete set of monitoring schemes showed that, with DRC technology, the roof periodic weighting interval decreased by 35.36%, and the hydraulic support pressure decreased by 17.56%. The theoretical analysis was consistent with the measured results. Therefore, the DRC technology is feasible and effective to ensure mining safety at the working face.

2

The seismogenic tectonic of Anchorage Mw7.0 Earthquake in Alaska, November, 30, 2018

Lei Dongning, Yang Gang

Acta Geophysica

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2020

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Vol. 68, no. 3

619--626

EN

The Mw7.0 Anchorage earthquake is most signifcant event since 1964 Mw9.2. Far away subduction zone trace, thus the seismogenic structure and failure plane are not clear and keep disputed. Based on published data, including faults, aftershock, focal mechanism solutions and source fault model and so on, we make comprehensive analysis and discussion. We think that this earthquake belongs to plate subduction event, without relationship with Castle Mountain fault and Border Ranges fault for seismogenic structure, only earthquake-controlling structure. Both faults are not responsible for the Anchorage earthquake. The actual seismogenic fault plane has a south-to-north trending and dips to east, which is corresponding to the nodal plane I.

3

Holocene activity and seismic hazard analysis of faults in Damxung, Tibet

Yang Gang, Tang Yong, Lei Dongning, Hu Qing, Wu Jianchao

Acta Geophysica

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2020

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Vol. 68, no. 3

597--604

EN

Based on interpretation of remote sensing and geological feld survey result, three secondary faults are distributed in parallel in Damxung of the southeastern piedmont fault of Nyainqentanglha mountain, which form landform profle across normal faults of graben due to cut platform margin of grade I terrace scarp formation. Through researching the displacements and the collected sediments dates, it is obtained that the horizontal slip rate is about 0.6 mm/a (millimeter per year), and the vertical slip rate is about 1.7 mm/a since 4 ka B.P. (kilo years before present). The northern margin of Damxung basin is a seismic gap, which continuously accumulated strain energy is not released in the M7.5 Damxung earthquake and the M8.0 Yangbajain earthquake. The fracture length of the seismic space can be regarded as the minimum length of potential surface rupture. The maximum moment magnitude of potential earthquakes is at least M6.8.in northern margin of Damxung basin the normal fault magnitude estimation formulas from Wells and Coppersmith (Bull Seismol Soc Am 84(4):974–1002, 1994).