| 摘要 |
PROBLEM TO BE SOLVED: To prevent landslides of a pit wall in the case of excavating a medium hard rock layer, a soft rock layer and natural ground where rocks are likely to fall by providing a gripper in such a manner that the pressing force is adjustable. SOLUTION: A main gripper P comprises a main gripper shoe 10, a main gripper jack 11 for expanding the gripper shoe 10, and a hydraulic circuit for driving the jack 11. In the case of excavating a medium hard rock layer or a soft rock layer where cracks are easily caused in the tunnel pit wall by the pressing force of the gripper P, the pressing force of the gripper P applied to the upper half part above the center of the tunnel, the pit wall of which is easy to collapse due to influence of gravity is lowered, and the pressing force of the gripper P applied to the lower half part below the center of the tunnel, the pit wall of which is hard to collapse is increased. In this case, the respective hydraulic circuits of the upper main gripper jack 11a and the lower main gripper jack 11b are controlled independently to regulate the pressure of each jack 11a, 11b. |
