| 摘要 |
PURPOSE:To form a groove-shaped continuous pit capable of forming a free surface having high accuracy to a bedrock. CONSTITUTION:Annular pits are shaped in a bedrock surface 1 by operating annular boring drills 13 loaded on a drill 10 while the directions of the drilling of the boring drills 13 are controlled as using core sections 1A being formed in a cantilever cylindrical shape and left and formed in a bedrock as guide cores. Boring drills 14 means are moved so as to shape specified superposing sections to annular pits 3 at places adjacent to the core sections 1A, and annular pits 4, are formed successively while leaving and forming the core sections 1A in the bedrock, thus forming a continuous groove-shaped section. |
