176,380 research outputs found

    Assessment of the effectiveness of treatment methods on Eucalyptus grandis yielding pencil props

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    Abstract: Supporting of underground hanging-walls is an important task that ensures a safe working environment and a continuous opening in underground mining operations. Underground stope support systems such as yielding pencil props, packs, tendons and backfill are used to stabilise hanging-walls in excavations to reduce or eliminate falls of ground and rock-bursts. The brushingoff of the pod end of an installed E. grandis pencil prop is the initial yielding part of the support unit under load. This failure mechanism allows inelastic hanging-wall to converge or vertically dilate while the support unit maintains contact with the rock unit without losing its support integrity (i.e. it does not buckle). Higher Moisture Content (MC) in yielding pencil props allows the props to fail according to the expected mechanism. Tonnes of timber products are wasted annually due to severe cracking / checking during the storage phase. Physical deterioration in a form of cracks of more than 10 mm wide and longer than 1/3 of the longitudinal dimension of the yielding pencil prop are criteria used by timber units’ suppliers to reject yielding pencil props...M.Ing. (Engineering Management

    Peculiarities of the underground mining of high-grade iron ores in anomalous geological conditions

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    This paper is dedicated to research into the geological peculiarities, shape of the ore body and the occurrence of the host rocks in the hanging wall of the Pivdenno-Bilozerske deposit , as well as their influence on the degrees and quality of high-grade iron ore extraction. It is noted that in the interval of 480 – 840 m depths, a decrease is observed in the stability of the natural and technogenic massif, which is caused by the increase in rock pressure with depth, the influence of blasting operations on the massif and the difference in geological conditions. This has led to the collapse of hanging wall rocks and backfill into the mined-out space of chambers in certain areas of the deposit, the dilution of the ore and deterioration of the operational state of the underground mine workings. Attention is focused on the causes and peculiarities of consequences of the collapse of the hanging wall rocks during ore mining, which reduce the technical and-economic indexes of the ore extraction from the chambers. A 3D-model of an ore deposit with complex structural framework has been developed, which makes it possible to visually observe in axonometric projection the geological peculiarities and the shape of the ore body. The parameters have been studied of mining chambers in the 640 – 740 m floor under different changing geological conditions of the ore deposit and hanging wall rocks occurrence – the northern, central and southern parts. The difference in the iron content in the mined ore relative to the initial iron content in the massif has been defined as an indicative criterion of the influence of changing conditions on the production quality. The reasons have been revealed which contribute to the collapse of the rocks and the subsequent decrease in the iron content of the mined ore in ore deposit areas dif- fering by their characteristics. It has been determined that within the central and half of the southern ore deposit parts with a length of 600 m, an anomalous geological zone is formed, the manifestation of which will be increased with the depth of mining. It was noted that within this zone, with the highest intensity and density of collapse of hanging wall rocks, the influence of decrease in the slope angle and change in the strike direction are of greatest priority, and such geological factors as a decrease in hardness, rock morphology, deposit thickness increase this influence significantly. To solve the problems of the hanging wall rocks’ stability, it is recommended to study the nature and direction of action of gravity forces on the stope chambers in the northern, central and southern parts, as well to search for scientific solutions in regard to changes in the geometric shapes of stope chambers and their spatial location, improving the order of reserves mining in terms of the ore deposit area, the rational order of breaking-out ore reserves in the chambers with changing mining and geological conditions of the fields’ development

    Slip inversion along inner fore-arc faults, eastern Tohoku, Japan

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    The kinematics of deformation in the overriding plate of convergent margins may vary across timescales ranging from a single seismic cycle to many millions of years. In Northeast Japan, a network of active faults has accommodated contraction across the arc since the Pliocene, but several faults located along the inner fore arc experienced extensional aftershocks following the 2011 Tohoku-oki earthquake, opposite that predicted from the geologic record. This observation suggests that fore-arc faults may be favorable for stress triggering and slip inversion, but the geometry and deformation history of these fault systems are poorly constrained. Here we document the Neogene kinematics and subsurface geometry of three prominent fore-arc faults in Tohoku, Japan. Geologic mapping and dating of growth strata provide evidence for a 5.6–2.2 Ma initiation of Plio-Quaternary contraction along the Oritsume, Noheji, and Futaba Faults and an earlier phase of Miocene extension from 25 to 15 Ma along the Oritsume and Futaba Faults associated with the opening of the Sea of Japan. Kinematic modeling indicates that these faults have listric geometries, with ramps that dip ~40–65°W and sole into subhorizontal detachments at 6–10 km depth. These fault systems can experience both normal and thrust sense slip if they are mechanically weak relative to the surrounding crust. We suggest that the inversion history of Northeast Japan primed the fore arc with a network of weak faults mechanically and geometrically favorable for slip inversion over geologic timescales and in response to secular variations in stress state associated with the megathrust seismic cycle.Funding was provided by a grant from the National Science Foundation Tectonics Program grant EAR-0809939 to D.M.F. and E.K., Geologic Society of America Graduate Research Grants, and the P.D. Krynine Memorial Fund. The authors thank Gaku Kimura, Kyoko Tonegawa, Hiroko Watanabe, Jun Kameda, and Asuka Yamaguchi for scientific and logistical support, and Kristin Morell for comments on early versions of the manuscript. We also thank Yuzuru Yamamoto and Kohtaro Ujiie for their detailed reviews and suggestions for improvement to the manuscript. The authors acknowledge the use of the Move Software Suite granted by Midland Valley's Academic Software Initiative. Geologic, structural, stratigraphic, and chronologic data used herein are accessible in manuscript figures, and in the citations therein. Input geologic data for trishear kinematic modeling can be accessed in Table 1 and in the supporting information. (EAR-0809939 - National Science Foundation Tectonics Program grant; Geologic Society of America Graduate Research Grants; P.D. Krynine Memorial Fund

    The Mahogany Peaks fault, a late Cretaceous-Paleocene(?) normal fault in the hinterland of the Sevier orogen

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    The contact separating Ordovician rocks from the underlying lower part of the Raft River Mountains sequence, northwestern Utah, is reinterpreted as a large-displacement low-angle normal fault, the Mahogany Peaks fault, that excised 4-5 km of structural section. High delta(13)C values identified in marble in the lower part of the Raft River Mountains sequence suggest a Proterozoic, rather than Cambrian age. Metamorphic conditions of hanging wall Ordovician and footwall Proterozoic strata are upper greenschist and middle amphibolite facies, respectively, and quantitative geothermometry indicates a temperature discontinuity of about 100 degrees C. A discordance in muscovite Ar-40/Ar-39 cooling ages between hanging wall and footwall strata in eastern exposures, and the lack of a corresponding cooling age discordance in western exposures, suggest a component of west dip for the fault. The juxtaposition of younger over older and colder over hotter rocks, the muscovite cooling age discordance with older over younger, and top-to-the-west shearing down-structure are consistent with an extensional origin. The age of faulting is bracketed between 90 and 47 Ma, and may be synchronous with footwall cooling at about 60-70 Ma. Recognition of the Mahogany Peaks fault, its extensional origin, and its probable latest Cretaceous to Paleocene age provides further evidence that episodes of extension at mid-crustal levels in the hinterland of the Sevier orogenic belt were synchronous with protracted shortening in the foreland fold and thrust belt, and that the Sevier orogen acted as a dynamic orogenic wedge

    The Mesozoic and Tertiary deformational history of the Arica Mountains, southeastern California

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    M.S. University of Kansas, Geology 1997The Arica Mountains lie along the northern edge of the Maria fold and thrust belt and along the western boundary of the Colorado River extensional corridor. The range lies within the hanging wall of the regional detachment fault system. Rocks within the AricaMountains consist of metamorpho.sed Paleozoic cratonal and Mesozoic metasedimentary rocks that have been ductilely deformed and juxtaposed against a Precambrian gneissic complex. Unfoliated Cretaceous granodiorite intrudes the Precambrian assemblage. Large-scale, isoclinal folds deform the Paleozoic and Mesozoic metasedimentary rocks and are refolded by a second system. These refolded folds are cut by the Priest Mine shear zone, a high-angle sinistral shear zone, that omits strata. These previously formed structures are truncated by the Arica shear zone a moderately-dipping normal-sense ductile shear zone. A felsite dike crosscuts the Arica shear zone and yields a U-Pb (zircon) age of 108 - 114 Ma. A northeast dipping low-angle normal fault of presumed Tertiary age displaces hanging-wall rocks >800 meters to the east-southeast. Brittle faults bound the range to the west, south and east. The Arica Mountains have been tilted a minimum of 30° to the west, and prior to Tertiary extension, the range resided in a position close to the northern end of the Little Maria Mountains. Tertiary sediments in depositional contact with pre-Tertiary basement rocks within the Arica Mountains indicate that the range was at shallow-crustal levels at the onset of Tertiary extension. Synextensional basin deposits within the hanging wall of the Colorado River extensional corridor have been divided into six structural domains. A new domain, the Rice domain, is proposed based on correlations of Tertiary deposits within the Arica and Riverside mountains. Based on varying dips within synextensional basin deposits, fault blocks within the Rice domain were first tilted between 23 and 20 Ma. This was followed by a second episode of tilting which occurred between 20 and 18 Ma. The presence of megabreccia deposits along the western trace of the breakaway zone suggest that movement along this segment of the zone began near its present position during the early Miocene

    Slip rates on the Chelungpu and Chushiang thrust faults inferred from a deformed strath terrace along the Dungpuna river, west central Taiwan

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    The Chelungpu fault produced the September 1999 M_w = 7.6 Chi-Chi earthquake, central Taiwan. The shortening rate accommodated by this structure, integrated over several seismic cycles, and its contribution to crustal shortening across the Taiwanese range have remained unresolved. To address the issues, we focus our study on the Chelungpu and Chushiang thrust faults within the southernmost portion of the Chi-Chi rupture area. Structural measurements and available seismic profiles are used to infer the subsurface geometry of structures. The Chushiang and Chelungpu faults appear as two splay faults branching onto a common ramp that further north connects only to the Chelungpu surface trace. We survey a deformed strath terrace along the Dungpuna river, buried under a 11,540 ± 309 years old fill deposit. Given this age, the dip angles of the faults, and the vertical throw determined from the offset of the strath terrace across the surface fault traces, we estimate slip rates of 12.9 ± 4.8 and 2.9 ± 1.6 mm/yr on the Chelungpu and Chushiang faults, respectively. These yield a total shortening rate of 15.8 ± 5.1 mm/yr to be absorbed on their common decollement at depth. This total value is an upper bound for the slip rate on the Chelungpu fault further north, where the Chushiang fault disappears and transfers shortening to adjacent faults. Combining these results with the recently constrained shortening rate on the Changhua blind thrust reveals that all these frontal faults presently absorb most of the long-term horizontal shortening across the Taiwanese range. They thus stand as the major sources of seismic hazards in this heavily populated area. The return period of earthquakes similar to the Chi-Chi event over a ∼80 km long stretch of the Western Foothills is estimated to be ~64 years. This value is an underestimate because it assumes that all the faults locked during the interseismic period slip only during such large events. Comparison with historical seismicity suggests that episodic aseismic deformation might also play a major role in accommodating shortening
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