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Number of results: 7
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Abstract

About 1600 joint fractures were measured in tillites of the Upper Hecla Hoek Formation on the southern shore of Bellsund. Measurements were collected in 12 areas between the Renardbreen and Tjörndalen. Ray diagrams and contour diagrams of joint fractures, and contour diagrams of joint fractures after rotation to pre-folding position were made for each area. The preliminary analysis of diagrams indicates 2 conjugated joint sets: ca. 60°—120° and 0°—30°. This joint system is probably older than folding and was originated under ENE—WSW to NE—SW stress.
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Abstract

Lower Carboniferous limestone has been extracted in the “Czatkowice” open-pit hill-slope quarry in southern Poland since 1947, for the needs of metallurgical and building industries, as well as farming. We can distinguish two aquifers in the Czatkowice area: the Quaternary porous aquifer and the Carboniferous fissure-porous one. Two vertical zones representing different hydrodynamic characteristics can be indentified in the Carboniferous formations. One is a weathering zone and the other one the zone of fissures and interbedding planes. Groundwater inflows into the quarry workings have been observed at the lowest mining level (+315 m above the sea level (asl)) for over 30 years. This study concerns two hypotheses of the sources of such inflows originating either from (a) the aeration zone or from (b) the saturation zone. Inflows into the quarry combine into one stream flowing gravitationally to the doline under the pile in the western part of the quarry. This situation does not cause a dewatering need. Extending eastward mining and lowering of the exploitation level lead to increased inflows.
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Abstract

The efficient protection (support reinforcement) of a wall and heading crossing ensures continuity of the production cycle, and that is a quick moving of the scraper conveyor to the wall. Using low or high bolting as a support reinforcement element in wall and heading crossings allows for the elimination of traditional methods of maintaining longwall-gate crossings, and therefore allows for the efficient use high performance modern wall complexes. The paper presents the long underground experience, of the Knurów–Szczygłowice mine of efficient support wall and heading crossing maintenance, which was bolted to the rock mass with the usage of two pairs of bolts, showing full technical and economical usefulness of this support reinforcement method. The article also highlights work safety and the increasingly common usage of endoscopies when specifying the range of crack areas which directly effects the proper choice in number, load-capacity and length of the used bolts. The underground studies the measurements of the reach of the zones of fracturing and roof stratification (using endoscopes and wire type stratification meters) and the laboratory tests (using the test stand) have allowed to determine the safety factor for maintenance of the longwall gangway crossing, directly resulting in the necessity to install additional reinforcement. The value of the safety factor Sbsc-ch greater than 1 is advantageous and safe, and the value less than or equal to 1 can lead to a significant deterioration of the conditions of maintenance of a wall and heading crossing which was bolted.
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Abstract

7N01-T4 aluminum alloy was welded by metal inert gas welding and the influence of V-groove angle on joint fatigue properties was investigated. The results indicate that the volume of fusion zone (FZ) and the grains in FZ become small when the groove angle decreases to 50° from 70°. Most pores distribute at the FZ edge and fewer pores are formed in the small angle joint. The fatigue crack mainly initiates at the transition region between the weld passes due to the pore concentration. The small angle contributes to increasing joint fatigue properties, especially at the low stress level. The fatigue strength of 50° joint is 103.06 MPa which is 15.3% higher than that of 70°joint.
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Abstract

Wider application of silicon carbide (SiC) is anticipated for increasing the durability of various structural facilities. For this study, SiC was fabricated with decreased electrical resistivity for precision electrical discharge machining. Two-step reaction sintering by infiltration of molten Fe-Si alloy was applied for SiC fabrication. The procedure included first sintering at 973 K in Ar gas atmosphere and second sintering by spontaneous infiltration of molten Fe-75%Si alloy at 1693 K in vacuum. The sintered structure porosity became very low, forming 3C-type SiC. Results confirmed that molten Fe-75%Si alloy infiltration occurred because of reaction sintering. The electrical resistivity of the sintered SiC infiltrated by molten Fe-75%Si alloy can be improved to be two orders of magnitude lower than that by molten Si, consequently maintaining the high performance of SiC.
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Abstract

Mining the lower seams in a sequence of shallow, closely spaced coal seams causes serious air leakage in the upper goaf; this can easily aggravate spontaneous combustion in abandoned coal. Understanding the redevelopment of fractures and the changes in permeability is of great significance for controlling coal spontaneous combustion in the upper goaf. Based on actual conditions at the 22307 working face in the Bulianta coal mine, Particle Flow Code (PFC) and a corresponding physical experiment were used to study the redevelopment of fractures and changes in permeability during lower coal seam mining. The results show that after mining the lower coal seam, the upper and lower goafs become connected and form a new composite goaf. The permeability and the number of fractures in each area of the overlying strata show a pattern of „stability-rapid increase-stability“ as the lower coal seam is mined and the working face advances. Above the central area of goaf, the permeability has changed slightly, while in the open-cut and stop line areas are significant, which formed the main air leakage passage in the composite goaf.
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Abstract

Influenced by the dynamic pressure of the front abutment pressure and the lateral abutment pressure, large deformation of surrounding rock occurs advancing working face in the entry heading adjacent to the active longwall mining face. Based on the cause analysis of entry large deformation, a new technology was put forward to solve the problem, and the designing method of drilling hole parameters for directional hydraulic fracturing was formed. Holes are drilled in the entry or in the high drainage entry to a certain rock layer over the adjacent working face, hydraulic cutting or slotting at the bottom of a borehole were also applied in advance to guide the hydraulic fractures extend in expected direction, through which the hard roof above the coal pillar can be cut off directionally. As a result, the stress concentration around the entry was transferred, and the entry was located in a destressing area. The field test at Majialiang coal mine indicates that the propagation length of cracks in single borehole is more than 15 m. After hydraulic fracturing, the large deformation range of the entry is reduced by 45 m, the average floor heave is reduced by 70%, and the average convergence of the entry’s two sides is reduced by 65%. Directional hydraulic fracturing has a better performance to control the large deformation of the dynamic pressure of the entry heading adjacent to the advancing coal face. Besides, it can improve the performance of the safety production.
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