Assertion: pile bore | /r/HasProperty | excavated by main drill bits
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Source sentences:
text: In the under-reaming pile bore excavator according to the present invention, a straight pile bore is first excavated by the main drill bits provided at the tip of the excavator with the slidable wing bits held at their uppermost position, and then the under-reamed part of the pile bore is excavated by moving the slidable wing bits downward and by extending them outward along the guide rails by the weight of masses mounted onto the slidable wing bits, with the main drill bits in position at the bottom of the pile bore.