| 摘要 |
PURPOSE:To form a high-density crushed stone-column as well as obtain a light-weight and compact driver by a method in which an outside screw for drilling and an inside screw for consolidation which is turnable in the outer screw are provided and both of the screws are interlocked by only one drive source. CONSTITUTION:An inside screw 12 idly turns in an outer screw 11. However the screw 11 turns with great torque slowly at a fraction of the speed of the screw 12 in the direction of excavation for drilling. The screw 12 is pushed out, the cover 36 on the tip of the screw 11 is opened, and crushed stones are introduced into a casing 11a. The screws 12 and 11 are turned mutually in the opposite directions, and crushed stones are pressed downwards to form a crushed stone-drain 39. High-density crushed stone column can thus be formed, and a light-weight and compact driver can be obtained.
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