Abstract
The phenomenon of great difference of mishap rate for roof collapse in the stope of a mine between day and night has been found in accordance with our observation in operational jobsite and the informations recorded over past 30 years,witch is regarded as a phenomenon of gravitational effect and is in the know by the inference of Newton’s Gravitational Principle that in general no one can explain it clearly by means of “mine pressure”,neverthless the major reason is that the direction of pressure on the stope roof between day and night is oppsite to the direction of the lunar gravitation (normal component force),and after it superposed onto the terrestmal gravity,their composite forces (PC) are different so that the pressure on roof is also various,greater in the night time and lighter in the daytime.this is why the roof collapse occurred in the nighttime is greater than that in the daytime.
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