نتایج جستجو برای: Room and pillar
تعداد نتایج: 16839779 فیلتر نتایج به سال:
The collapse of abandoned room-and-pillar mines is often violent and unpredictable. Safety concerns often resulted in mine closures with no post-mining stability evaluations. As a result, large amounts of land resources over room-and-pillar mines are wasted. This paper attempts to establish an understanding of the long-term stability issues of goafs (abandoned mines). Considering progressive pi...
In some instances, extensive room-and-pillar workings can collapse with little warning and pose a serious risk to underground miners. Traditional strength-based pillar design methods applicable to coal or hard-rock mines use a factor of safety defined as pillar strength divided by pillar stress. Factor of stability, defined as local mine stiffness divided by post-failure pillar stiffness, may o...
Selecting a suitable pillar recovery method is one of the most important issues in the room and pillar mining. The main purpose of this study is to compare two methods for pillar recovery in Tabas central coal mine (TCM). Among the existing methods, the two methods, “Modified split and fender” and “Shortwall” are chosen for the numerical modeling. The three dimensional finite difference method ...
in this thesis, a better reaction conditions for the synthesis of spirobarbiturates catalyzed by task-specific ionic liquid (2-hydroxy-n-(2-hydroxyethyl)-n,n-dimethylethanaminium formate), calcium hypochlorite ca(ocl)2 or n-bromosuccinimide (nbs) in the presence of water at room temperature by ultrasonic technique is provided. the design and synthesis of spirocycles is a challenging task becaus...
abstract in first part of this project, the use of a new and biguanid-like catalyst supported on silica as a recyclable catalyst provides a new route for the synthesis of a variety of arylalkylidene rhodanine derivatives through knoevenagle reaction in at present of solvent at room temperature. rhodanine derivatives and especially arylalkylidene rhodanines have proven to be attractive compound...
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