Abstract
In the comprehensive research on the surface subsidence occurred by various underground longwall mining in various countries that was reported previously, the author analyzed relationship between ki (breaking factor of fallen debris) and various mining methods or various physical characteristics of the rock strata. Specifically speaking, the author calculated various ki in the solid-state single seam and multipass mining carried out at Kushiro Colliery, and in various mining applied in England. As a result of the studies, it was found that ki value drastically changes according to the difference of physical characteristics of rock strata, and the disturbance of rock strata above goaf by secondary mining as well. With regard to the outcome of the studies, the author proved that the solidification of fallen debris after 2 years of termination of mining at the top lift has sufficient strength to be supported by the shield supports at lower lift under the circumstance of only 100 m below the surface. And the presentation mentioned above was eventually accepted by the Bureau of Mines, United States Department of Interior, and proposal to the US National Project with an idea to apply the Multi-step slicing method was placed to order as a first occasion for the Japanese Coal Mining Industry.
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