Deep foundation excavator

A deep foundation excavator comprising:

• an automotive vehicle body;
• and
• a working mechanism disposed in the vehicle body,
• wherein the working mechanism includes:
• a boom disposed in the vehicle body;
• an arm disposed in a tip end of the boom;
• a bucket raising/lowering and opening/closing device disposed in the arm;
• and
• a clamshell bucket that is disposed to be capable of raising and lowering to the arm and excavates a vertical shaft by a raising/lowering movement and an opening/closing movement of the bucket raising/lowering and opening/closing device,
• wherein the bucket raising/lowering and opening/closing device includes:
• a raising/lowering cylinder disposed in the arm;
• a first raising/lowering sheave and a first opening/closing sheave that are attached to one end side of the raising/lowering cylinder and move in an expansion/contraction direction of the raising/lowering cylinder;
• a second raising/lowering sheave that is disposed in the arm to be separated from the first raising/lowering sheave in the expansion/contraction direction of the raising/lowering cylinder;
• a second opening/closing sheave that is disposed in the arm to be separated from the first opening/closing sheave in the expansion/contraction direction of the raising/lowering cylinder;
• an opening/closing cylinder that is disposed in the arm and moves the second opening/closing sheave to be closer to and to be separated from the first opening/closing sheave;
• a raising/lowering rope having one end in a length direction attached to the arm, the other end attached to the clamshell bucket and an intermediate portion wound around the first raising/lowering sheave and the second raising/lowering sheave;
• and
• an opening/closing rope having one end in a length direction attached to the arm, the other end attached to the clamshell bucket and an intermediate portion wound around the first opening/closing sheave and the second opening/closing sheave,
• wherein the bucket raising/lowering and opening/closing device further includes:
• a slack adjustment cylinder that is disposed in the arm and expands and contracts for adjusting the slack of the opening/closing rope;
• and
• a slack adjustment sheave around which an intermediate portion of the opening/closing rope is wound in a state of being attached on one end of the slack adjustment cylinder and that moves in a direction of being closer to and being separated from the second opening/closing sheave in response to an expansion/contraction movement of the slack adjustment cylinder, and
• wherein the bucket raising/lowering and opening/closing device further includes:
• an opening/closing operation tool configured to operate the opening/closing cylinder;
• a raising/lowering operation tool configured to operate the raising/lowering cylinder;
• a detector configured to detect whether or not a tension acting on the opening/closing rope is equal to or less than a predetermined value;
• a cylinder switching valve configured to switch an operation target of the opening/closing operation tool from the opening/closing cylinder to the slack adjustment cylinder when the detector detects that the tension acting on the opening/closing rope is equal to or less than the predetermined value;
• and
• a cylinder contraction device configured to contract the slack adjustment cylinder when the raising/lowering operation tool is operated to a raising side to raise the clamshell bucket.