赤平炭鉱におけるリングカッタの開発について

抄録

The development of the large diameter boring by ring cutter was required for the alternative safety construction method of large diameter holes to compensate the lack of skilled labours for raise and drift construction, and other various relevant aspects.Conventional large diameter borings require to break all rocks within the hole, whic means high cost requirements and less effective operations consequently.
Sumitomo Akabira Colliery introduced the large diameter boring by ring cutter to avoid the demerits of conventional methods.In July 1978, the first test of 550mm diameter was carried, then 770mm diameter test was tried progressively. Through the test, the disking phenomenon which has no direct relations with joints or cracks of strata was confirmed. This disking phenomenon occurred expectedly in the practical operations, which made possible for the smooth improvement of further larger diameter boring. However, no disking phenomenon was recognized in some area exceptionally, where wedgeshaped breaker was fitted additionally to the cutter to obtain sufficient results. Now, large diameter borings of 1, 500mm diameter are possible and the flexible selection of diameters is applied according to the purpose, that is, ventilation holes for decreasing the underground high temperature caused by mine deepening, effective countermeasures for gas outburst, etc.
Recently, horizontal large diameter borings upto 30m has been possible using this method, and further horizontal long boring operation is possible if high power machine is introduced.
Regarding the cutting width of the ring part, it is fixed to 40mm width and single cone rotary bits are applied in stead of hard metal bits to decrease the cutting losses.The method is also applied for the advanced boring in the drift sinking operation. Thus the wide range of usages of this method is hopefully expanded to various ways.