Civil Engineering Reference
In-Depth Information
Figure 3.20
An underreaming tool in the open or working position. (Photograph courtesy of Stent
Piling.)
enter the bore. It is however important that loose material does not remain at the pile
toe and a suitable means of removing this is required if remote inspection is used. The
sequence of construction for a large diameter rotary bored pile with an underream is
shown in Figure 3.21.
Although the sliding Kelly bar and fixed rotary table is a common arrangement,
an hydraulically driven motor which slides in vertical guide rails can be mounted
on the top of the drilling stem. Because of the weight of such a motor, this sys-
tem is more popular in the smaller-diameter continuous flight auger (CFA) rigs (see
section 3.5).
At one time there was interest in a remotely controlled wire line-suspended rotary
drill in which a submersible electric drive motor is mounted directly over a triple
cutting head. There is no torque to be resisted by the rig with this arrangement, and in
suitable ground deep holes could be drilledwithout any drill stemhandling or extension
problems. The Tone Boring Co. Ltd. of Japan manufactured the drill (Figure 3.22).
