PURPOSE: To reduce auger torque at the time of drilling due to a friction reducing effect, to improve earth removal efficiency, or to sufficiently reduce resistance at the time of erecting a precast pile in a bored precast pile construction method using mechanical drilling, whereby a precast pile can be buried and installed in the ground quickly and efficiently.
CONSTITUTION: An earth auger 4 is lowered while being rotated to drill the ground E, and a bubble manufacturing plant 8 is operated concurrently with the above operation, whereby bubbles generated by a bubble generator 14 are ejected from the tip of the auger 4 through a swivel joint 6. The bubbles obtained by mixing air with an aqueous solution of water-soluble high polymer are different from the conventional bubbles obtained by using a surfactant or the like, and though the expansion ratio of the obtained bubbles is low, the tackiness and gravity are large so as to effectively reduce frictional resistance between soil particles, or between the soil particles and the earth auger 4 or a precast pile 20. Thus, the auger torque at the time of drilling can be reduced, and the earth removal efficiency can be improved, or the resistance at the time of erecting the precast pile 20 in a drilled hole 30 can be reduced sufficiently.
SAITO KIYOSHI
NAKAJIMA SHINYA
KOYAMA HIROSHI
