Browsing by Author "Akram, Muhammad"

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    The effect of zero point charge environment on rock fracture behavior
    Akram, Muhammad (Virginia Tech, 1991-06-06)
    This experimental investigation was conducted to assess the effect of zero point of charge (ZPC) environment on fracture behavior of rocks. The material parameters selected for this purpose were fracture toughness and specific work of fracture. These properties were determined for three rock types in five environments. Semi-circular bend specimens of dolomitic limestone, Sioux quartzite and Westerly granite were tested in aqueous solutions of aluminum chloride, calcium chloride and polyethylene oxide, all at ZPC conditions. These rocks were also tested in atmospheric air and distilled deionized water. For every rock type, the results obtained for the tests done in each of the ZPC environment were statistically compared with the results in water. This comparison was also made for air and water. The average fracture toughness in each of the ZPC environments, for all three rock types, was found to be less than the corresponding average in water. The specific work of fracture results also indicated reduction in ZPC environments as compared to water. The statistical analysis of the results, however, showed that this reduction was significant in some but not all of the rock-environment combinations tested in this investigation.
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    Stability assessment of entry roofs in underlying multiple seam mines
    Akram, Muhammad (Virginia Tech, 1993-06-07)
    Entry roofs in underlying multiple seam mines are vulnerable to failure under the influence of stress transferred from the upper seam workings. Overburden depth, innerburden thickness, percentage of hard rock in the innerburden and relative location of pillars in the two seams are some of the factors known to influence stress transfer and ensuing instability in the lower seam. This study was undertaken to quantify the effects of these factors and to develop a comprehensive roof stability assessment model capable of predicting any instability in the lower seam entry roofs under given conditions of geology and loading. The finite element analysis technique was used to model a range of loading conditions and innerburden lithology. The innerburden thickness was varied from 50 to 20 feet. The innerburden lithology was varied in terms of percentage of sandstone and its location in the innerburden. Various loading conditions were simulated by changing the relative location of pillars in the two seams and by varying overburden depths from 300 feet to 1500 feet. Excessive horizontal stresses and unsymmetric loading were also simulated. The effects of these factors were quantified in terms of safety factors across the entry span. The finite element results were used to obtain curve-fitted equations for computing safety factors at roof corner and midspan for given conditions of innerburden thickness, percentage of sandstone in specified location, overburden depth and pillar arrangement. These results were verified by back analysis of case studies and then incorporated into a comprehensive roof stability assessment model.