To excavate a pit having high accuracy by sufficiently utilizing the original excavation capacity of a pit excavator regarding the pit excavator excavating a vertical shaft having comparatively large pit diameter and depth to a ground.
The pit excavator is constituted so as to have a first excavator excavating a leading pit 2 to a ground 1, a guide rod 4 inserted into the leading pit 2 formed by the first excavator and a second excavator 5 being guided by the guide rod 4 and excavating an excavation target pit 3 having a diameter larger than the leading pit 2 to the ground 1. A frame-shaped supporter 8 supporting the second excavator 5, a travelling body, a belt 9, making the frame-shaped supporter 8 travel, a travelling guide means, a rail 10, guiding the travelling of a travelling body so that the second excavator 5 is positioned just above the guide rod 4 and a positioning stop means, a stopper, stopping the travelling of the belt 9 so that the second excavator 5 is placed just above the guide rod 4 are installed at that time.
MURAOKA TADASHI
AIHARA YOSHIHIRO
SHIBA YOSHIMI
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