抄録
In Akabira Colliery, a decision was made to change the angle of influence for the cone-shaped shaft pillar from 60° to 80° in 1985. Mining in the former pillar areas started in 1986 and 2.2 million tons of coal was safely extracted before the mine closure in 1994.
Damages have been induced in four levels along the concrete block-lined shaft having length of 680m. It was concluded through observation of lining, monitoring of displacements along the shaft axis and three dimensional elastic stress analysis that the main factors which induced the lining damages are (1) fault slips due to increase of shear stress, (2) increase of vertical stress component or decrease of minimum principal stress in the horizontal plane and (3) stress concentration around roadways connecting to the shaft.
A consideration on a reasonable monitoring scheme for shaft damages was also shown.
