71. A 2.5 m thick coal seam lying at an average depth of 100 m has been developed by bard and pillar method. The width of the square pillars is 30 m (centre to centre) and the gallery width is 4 m. The average density of the overlying strata is 26 kN/m3 and the pillar strength is 4500 kN/m2. Extraction ratio during the development of the pillar is
72. Soutirage mining is the alternative name of
73. In room and pillar mining multiple faces are advanced but driving entries or rooms follows a definite pattern known as
74. What is the minimum size of coal pillar when the depth of coal seam from surface remains between 240 m to 360 m and gallery width does not exceed 3 m?
75. A haul ramp of 6% grade is to be constructed connecting a bench of 15 m height to the surface. If the cost of ramp construction is 1 million rupees per km, the cost of this ramp construction in million rupees will be
76. What is the standard of lighting required for the workplace of HEMM's of opencast mine?
77. Ratio of water and emulsion in hydraulic fluid is
78. Ring pattern drill holes are provided in
79. What will happen if a Booster fan is placed too far inbye of the neutral point in either intake or return?
80. A developed panel for a coal seam having incubation period of 6 months has 32 square pillars under extraction having size 25 m and height 3.0 m. Density of coal is 1.4 tonne/m3. Extraction ratio during depillaring is expected to be 75%. To depillar the panel within the incubation period, assuming 25 working days in a month, the production from the panel in tonne/day is
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