Abstract
A kind of rock and water outburst occurred several times at the deep level excavation of the shafts or the inclines in Yubari New Coal Mine in the 1970's. In this incident a large amount of groundwater containing dissolved gas flowed out with scaled rock and a crater was formed at the outburst trace.
In this study, the formation mechanism of the above crater was considered on the basis of the observational and the experimental results in order to obtain a prevention measure against the outbu st. Moreover, the shape of the crater was examined by applying the probability theory on material strength to the bending fractures of the scaled rock.
From these results, it became clear that the vertical angle of the crater depended on the coefficient of uniformity of the rock strength and the hydrostatic pressure gradient in the cover rock. And, the observational facts, which the vertical angle of the crater in sandstone was larger than that in shale, could be explained well. Consequently, it became possible to estimate the grouting depth at the prevention works site against the rock andwater outburst.
