Monitoring of stress and vertical displacement changes in a pillar during secondary mining at Kamaishi mine. A study on the method for measuring in-situ stress change with pressure cell. 2nd Report.

Abstract

Yoshifumi NOGUCHI3 and Takashi NARASAKA4In order to contribute safety secondary mining of one of pillars in Kamaishi mine, stress and vertical displacement changes in the pillar were monitored at two points during the recovery of the pillar for about 560 days until the secondary mining was almost completed.Two-dimensional stress change in the vertical cross-section was measured by using a pressure cell with eight strain gauges glued around inner wall of the cell, and the vertical pillar displacement was measured with a dial gauge between two rock bolts through a vertical rod.Main results obtained in this study are summarized as follows; 1)From the measurement of stress change in the pillar, it was concluded that the pillar is still stable during the secondary mining, which was consistent with other measurements carried out at the same time.2)The behaviour of the stress and vertical displacement changes in the pillar was quite different between two measuring points. This seems to be caused by the complexity of geology and geometry around the pillar, discontinuities and directions of absolute rock stresses. 3)As the large blasting more than 450 m away from the pillar affected the stress in the pillar, it is suggested that the pillars in the mine support rock pressure in collaboration. 4)The vertical displacement in the pillar was less sensitive to the mining excavations in comparison with stress change.