PURPOSE: To eliminate the slip of an excavation head for a casing and to prevent the casing from damage by interlocking locking pins projected to the excavation head with interlocking and fitting grooves provided to the circumferential step of the casing.
CONSTITUTION: Locking pins 5... are projected to an excavation head 4 radially at proper intervals in the circumferential direction. Interlocking and fitting grooves 10 and 10 capable of interlocking only from the direction of rotation of a casing 1 are provided to the circumferential step 9 of the excavating casiang 1. When the casing encounters with a bedrock R during the excavation, the rotation of the casing 1 is stopped, and the casing 1 is rotated in the direction of excavating rotation at a low speed in a state to insert the excavation head 4 up to the circumferential step 9 of the casing 1. As a result, the locking pins 5 are interlocked with the interlocking and fitting grooves, and the excavation head 4 is fixed to the casing 1. Then, the casing 1 is rotated at a specific speed to excavate the bedrock R.
FUJIKI HIDENORI
HONDA JOJI
SAKAMOTO TAKAYUKI
SANWA KIKO KK
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