In this paper, the auther describes on the possibility of presage the collapse around the underground cavity by the rock pressure measurement. For the measurement of the variation of rock pressure, the weighing cell is used. The cell consists of the wire strain gauges fixed on the tuff, which is covered with the cement mortar. As the preliminary test of the measurement, the concrete test brock having a weighing cell in the midst of it was compressed. The results are shown in fig. 1 and 2. For the measurement of strain, the strain meter was used. The measurements were performed at the Kamishi Mine, where a large collapse occured on March 30 and 31, 1952, and it was imagined that some accompanying collapse will occur. In fig.4 is shown the boundary of the collapse. The positions of the weighing cells are shown, in fig. 5 and 6. The results of the rock pressure variation are shown in fig.7 and 8. No.1 and 4 weighing cells were used for the measurement of horizontal component, land the other cells were of vertical component. From the results of fig. 7, 8 and of the phenomena obserued by mine workers, it is recogrized that it is possible to pressage the danger of the collapse by the long-dated measurement of the rock pressure variation.
In order to facilitate the measurement of ventilating pressure under-ground, we contrived a new type of apparatus to measure the difference of absolute pressure of two points Its principle is based on the fact that as air confined in a vessel of constant temperature and volume is kept constant, the air pressure at each point can be determined by comparing it with the confined air pressure Experiences of practical use of this apparatus proved that it gives more rapid and accurate results than others